Sail design

[Saint]

I've read this on sail making...
http://marina.fortunecity.com/breakwater/274/1999/0715/Index.htm

(Michalak's polytarp sail article)

How do I figure out where I put point 'd' on my own sail of different dimentions and how deep the draft of the sail is at that point? Feel free to point me to some place on the net to read up what I should do.

[George Ray]

Sailmaker's Apprentice by Emiliano Marino is a GREAT read but there are many others.

The creation of sail draft using three triangles is new to me and I have not seen it in any books on sailmaking, however it seems a reasonable approach.

Best of Luck,

[Todd Bradshaw]

I'm biting my tongue, but it's not working... You know what this is like? This is the sailmaking equivalent of writing an article that would explain how to paint your boat using a can of paint and a shaped charge. It would go into great, mathematical detail to explain how to precicely pack the explosives to blow the paint uniformly all over the hull. We can all probably muster up a pretty good idea of how it would turn out. The logical reaction of most rational folk would be to ask "Why not just get a paintbrush and paint your boat properly?"

The only difference here is that they are dealing in a subject matter that most people haven't studied, which allows them to baffle you with very official looking formulas and other B.S. - and what's worse is that in the process of spinning all this bull, they've even managed to make it more difficult than real sailmaking! Naturally, they've also included the obligatory "works great, all day, every day" to make sure the poor reader is suckered in. At that point, the true student should be asking the question "Compared to what?"

If that wasn't bad enough, it's a lousy sail! He has the point of maximum draft 27% of his 100" chord-width aft of the mast. Even super-fast, high-aspect boats like racing multihulls and iceboats don't place their maximum draft that far forward because it doesn't work. There isn't a plywood dinghy on the planet that should be sailing with 9% draft placed 27% aft. It's Stall City and the only way to expect any kind of halfway decent performance is to crank the outhaul enough to bend the crap out of the mast and get rid of most of that draft.

Aside from the obvious durability and long-term stability differences between real sailcloth and materials like polytarp or Tyvek, sailmaking is sailmaking. You can make a REAL sail from polytarp and it's no more complex to design and build than this abortion is. You can still use carpet tape or duct tape, or whatever they're using instead of sewing and you can still do it with a few large chunks of plastic, but it will be a real sail and during the process you'll learn the how and why of what your doing properly.

Marinos book is excellent. For a less expensive, yet shorter and somewhat more straight to the point explanation, get a copy of Jim Grant's booklet on Mainsail Construction from his Sailmaker's Series. He is the founder of Sailrite and they sell it on their website.

As for this turkey, do yourself a favor and delete the bookmark.

[Todd Bradshaw]

OK, so that I wouldn't be accused of "hit and run" here, I whipped up a little PDF file that shows how a sail like this one should really be designed and constructed. It doesn't go into finishing details as I have no clue how the polytarp people do that stuff and really don't want to know. It also doesn't list any dimensions, but I think you'll be able to fill those in yourself without a problem. What it will do is show you how real sailmakers might design such a sail, whether it's Dacron, polytarp or made out of woven dog fur.

You may want to use the Sailrite mast bend measuring method quoted on the polytarp website - but be advised that he quoted Jim's method incorrectly (too bad he lost the book, he could have used it). The amount of weight that is normally used for that test is 1/3 of the sail's square-footage in pounds, not 1/2 of the square footage in pounds.

Anyway, the PDF is small (about 24K) but it's eleven pages of text and drawings. You could also design and build a real, Dacron sail with it just as easily. A supplemental text like Grant's or Marino's is suggested to fill in the blanks and further explain issues that were only touched on, but this will show you the basics. If you like it, download it and save it because I don't know how long I'll leave it up there. If I'd pull a dozen or so more small sail types out of the big Box-O-Rigs on my Mac's hard drive and do similar stuff, I'd have another book!

Here's the file: Note that the illustration pages generally follow the text pages and unlike a book where you can read text and see drawings on the next page at the same time, you may want to occasionally scroll ahead to see the drawings on the next page as you go through the text.

http://webpages.charter.net/tbradshaw/!POLY-LA.PDF

[Saint]

Very impressive Todd, thanks. Good timing as well. I just finished reading the chapter on sail theory in Jeremy Howard-Williams' book "Sails". Quite a lot of theory.

The one thing I don't understand with your article is the seaming. What is a broad seam vs. a panel seam?

Also, I'm not sure if I have understood the process right. After laying out the sail, you then cut it apart and sew it back together to get the proper shape - don't you end up with a sail several inches shorter than you inteneded?

Would this process differ much for a bermuda sail and for a jib?

Marvin

[Todd Bradshaw]

A broadseam is just a planned and controlled widening of a portion of a panel seam, made by increasing the overlap of the two panels as you stick them together. It helps turn two flat panels into a 3-dimensional shape. Broadseams do the same basic job that those silly darts and tucks do for the polyrtarp guys - except broadseams do it properly and don't look like crap.

First you cut the tarp into a few big strips, Then you lay them over the lofting and rough-cut their lengths. Next you tape (or baste and sew if you're using real fabric) the panels together following the guidelines on the lofting. Then, after all panels are connected, you lay the sail over the lofting and cut the edges to their final shape. Since you allow a bit of excess when laying out and joining the panels and do your final trimming over the original lofting, the sail turns out just as you designed it, size-wise.

Aside from a few small features which were modified specifically for building a sprit-boom sail (like the straight-cut foot) most of this information is the same sailmaking method that would be used on any small, basic sail (or big sail for that matter). Various sail types will often have their own small issues which need to be addressed (things like specific reinforcements or shape adjustments which one type may need and a different type may not) but the basic building method is usually quite similar.

[Thorne]

Thanks Todd - very clear directions and diagrams.

[merlinron]

awesome once again, todd!
that really got me fired up to start learning what i can about sail design. i've pretty much got things sorted out about getting the hull built and have started on the frames and jig. the next area i really need to look into was sails.
initially, i'm wondering...
can you reccomend a some reading that looks at the gaff sail in particular. i would think it's shape would alter the basic rules concerning where the broad seam referance curve would be put. my mainsail is very highly peaked, but still, with the absence of a "sail head" in the usuall location, would that referance line simply be shifted back to terminate at some point on the gaff 2/3 to 3/4 of the sail total height( luff+gaff), or would be figured to terminate at a point extended equivelant to a sail's luff that would be against the mast, as a normal marconi would be. i would think the "rules" might differ a bit between a more or less traditionally defined gaff and one so highly peaked(?).......thanks.

[Bruce Taylor]

Stirring rant, Todd (hope it was therapeutic). And the .PDF is a thing of beauty.

Now, you know I respect your craftsmanship, but I want to put in a good word for the polytarp & carpet tape prototype. As you know, before you made the "Egyptian dacron" sails that I'm proud to use on my Piccolo and Blackfly I made do with quick-and-dirty polytarp sails. In each case, 20 dollars and a couple of hours with scissors and tape got me out on the water. With Piccolo (not what you'd call a high performance sailer!) the taped sails gave me a couple of years of fun before I got tired of their fragility and sloppy shape. With Blackfly (an untried design) I really wanted to to be sure the sailplan would work before investing in a proper sail.

The taped polytarp sails filled a gap, and it really was very cheap and easy to throw them together. They were not very durable (the Blackfly sail started coming apart after my third time out), and I arrived at the shape (such as it was) by wild guess. Fortunately, the standing lug is easy to trim and somewhat forgiving of slovenly sail design.

In short: no regrets! :)

[Boatmik]

Hi Todd,

That little PDF is a great resource - thanks for taking the time to put it together.

I have done enough sailing in a whole range of boats to know the ultimate in FAAAAAAST is a sail with broadseams.

However the old Laser sails seemed to sit very flat on the floor indicating a minimum amount of broadseaming. I don't know about their new pattern.

So is it possible to build an OK sail with luff round only?

Does making a sail with luff round only assume the sail will have to be cut fairly flat to work OK?

What do you think it would be possible to get away with as far as making a really simple sail?

Thanks
Michael Storer

[Todd Bradshaw]

Bruce, my objection to polytarp sails has never been about the material - it's the method used to make sails from it. The material is what it is. I don't think anyone actually believes it to be equal in stability, durability, strength or quality to real sailcloth (and if they do they're dreaming) but even so, there are proper methods and building/design practices which should be used to make a sail from any suitable material. It just really irks me when I find one of these step-by-step, "how to build it" websites where the author is teaching bad sailmaking. They frequently contain lots of official-looking math and other mumbo-jumbo, but show no evidence whatsoever that the author knows anything at all about making a sail. Even the most simple sailmaking principle - that the fabric needs to be properly oriented to the plan in order to achieve maximum strength and stability, is more often than not completely absent and not even mentioned. You don't want someone making your sails who isn't fully aware of and practicing that simple rule and a few others - and you absolutely don't want that person teaching you how to make your own sails! Who knows what other gaps there are in his knowledge? This guy even claims that at one time he owned a copy of Jim Grant's book "Make Your Own Mainsails". That's the one he misquoted for the mast bend test method. If he had actually bothered to read the book and learn some of the information that it contains, there's no way he'd design and make a sail the way he did.

I firmly believe that learning to build a sail properly is no more difficult or time-consuming that what these people are teaching and that the final product, even a first effort for a rank beginner, can easily be a far better sail than anything these "instructors" have ever produced. Certainly, there are some construction method tweaks needed due to physical differences between polytarp and Dacron, but a properly designed and properly cut sail is still just that and most of what these people are creating isn't even close.

Merlinron, at this point in time, Marino's book contains about 99% of the usable, available written info on gaff sail construction - both in terms of text and with a few drawings of examples that you can look at to see how the various techniques were used to generate their shapes. Understand right off the bat that a good gaff sail that sets nicely can be a very difficult thing to design and build. The shape of each edge and the sail area near it need to be designed nearly independently and then the whole thing essentially merged together into one big shape where they work together. When you then string it up and have a bunch of lines and fittings pulling at the corners and edges, a slight miscalculation or misalignment can make a big and stubborn wrinkle that's damned difficult to get out. If you are ever looking at building a new gaff main yourself, I'd go for a computer plotted kit in a heartbeat. You worry about the sewing, let the computer figure out the shaping.

The broadseams on a gaff sail vary, depending upon the cloth used and more importantly, the panel layout. As I mentioned before, you can't broadseam places which don't have seams. On a vertical-cut gaff or lugsail, broadseaming usually takes place along the head and foot edges and there may be some luff round, but seldom is there much broadseaming going on there because so few seams strike the luff - even when narrow-paneled as you cas see here. Vertically-cut gaff and lugsails usually have nearly all of their broadseaming inside zones like the pink shaded ones shown on the drawing.

http://www.imagestation.com/picture/sraid209/p9e3ddf644ef8e3d6eda62d627fab8a84/ee3e8fcb.jpg

On a cross-cut construction, the bottom of the broadseam curve is similar to that you might find on a 3-sided sail, but rather than intersecting the upper luff, it narrows and then makes a turn at the throat to go up and give some shape to the sail area in the head and along the gaff (where there will also usually be some head-round - similar to luff round to create upper sail draft). Since the curve roughly follows or relates to the sail's edge, the top portion of the broadseam curve on a high-peaked gaff would also be pointed higher than it would be on a low gaff. As you can see, trying to get all the curves and shaped edges working together on one of these guys can be quite a challenge.

Michael, Yes you can build a sail with round, but without broadseams - but you would need to use pretty soft fabric. It will give and/or stretch enough to allow the excess added-in by the luff curve to migrate aft toward the sail's middle and create draft. You could do it with cotton, but nearly everything offered in Dacron by the sailcloth manufacturers these days is too stiff and stable for it to work. You tend to end up with a big, vertical bloop just behind the mast and a pretty flat sail (very similar to the sailshape produced by really cranking down hard on the downhaul or cunningham on performance boats for an upwind leg). It's not generally something that you want happening all afternoon as your sail will be much flatter than what you had in mind when you originally designed and calculated the draft and luff curve. Once you get past the "reading about it" stage, broadseaming is actually pretty simple and generally not something to dread. Sails that don't work properly, on the other hand, should be something to dread, especially if they're your only source of propulsion.

There are some sail types that are cut absolutely flat with no luff curves or broadseaming. Batwings, for example are good for light, easily-powered hulls, like canoes. The wind pressure alone will bend them into a shallow foil shape, which is generally plenty of power for their hulls. Junk sails (Chinese lugsails) are also cut dead flat and have rather heavy battens that pretty much keep them flat in use. As far as I know, they work by magic, rather than the typical wing-shaped airfoil principles that we're all used to seeing, but they do work.

Here is one from concept drawing, to lofting, to finished sail, to rigged and out to the lake, ready for a test run. Notice that there are no edge rounds or broadseam curves at any time during the process. The luff is actually just slightly concave, which is sometimes done on lugsails to help provide luff tension on the unsupported edge flying out in front of the mast.

http://webpages.charter.net/tbradshaw/CL9.jpg

[merlinron]

once again todd, you can be relied upon to give replies to rookie's questions that are exactly what they are looking for....and much more!.
marino's book, amongst others, will be sought.
i have allot of time before i need to be thinking about whether i build my own or sew from a kit, or maybe evan go to some guy that might know what he's talking about.... ( now, who could that be?)...
right now, i'm thinking, "build my own, i know i can do it".... but i haven't built the boat yet, and by then i might come to my sences.

[Boatmik]

Junk sails (Chinese lugsails) are also cut dead flat and have rather heavy battens that pretty much keep them flat in use. As far as I know, they work by magic, rather than the typical wing-shaped airfoil principles that we're all used to seeing, but they do work.
Thanks for the new posting above too Todd.

The above posting of Todd's is the first pic I have ever seen for the broadseaming layout in a vertical cut sail - a few years ago I did a lot of looking for such a diagram and never found it - good on you for putting it up.
_____________________________

A poor sail is a poor sail and I have seen many awful concoctions over the years but my sense is that there are three stages of sailmaking depending on what you want.

Each stage will make the sail work much better, both in terms of general efficiency and in terms of extending the windrange, but even the most basic flat sail can work OK as Todd points out with canoe sails and junks.

There are valid reasons to make simpler sails.

1/ Flat cut sail - The most basic sail is one where the sail is designed to be dead flat. You don't need camber to get lift - eg cheap balsa wood gliders, insect wings. But you need allowances to take account of the amount the various sticks that are attached to the edges of the sails bend.

Years ago one of my clients decided to have a local tarpaulin manufacturer make up a totally flat sail for one of my designs. I was dead against the idea - but the boat sailed very nicely - but it was light with a generous sailplan and excellent foils.

(One man's "nicely" is another man's horror show! I have an extensive and quite successful racing background in small boats in a wide range of classes at club, state and a bit at national levels.)

Downside - is that a sail with camber/depth can develop more power for the same area in most wind strengths and most wind directions

I think in retrospect that a good part of the reason the flat sail worked OK on the boat above was that the sail area was generous - so the lower level of power per square foot of the flat sail was compensated for. A boat with a small amount of sail for the size may sail VERY poorly with a completely flat cut sail.

2/ Sails with luff round - This assumes that the fabric you are working with will have sufficient "bias distortion" to move the extra sail area added along the edges toward the middle of the sail where it belongs.

Bias distortion - all cloth has two thread directions at 90 degrees to each other - the cloth doesn't stretch much if tensioned along the threads - but if you pull at 45 degrees to both threadlines there can be much more stretch = bias distortion

Polytarp has heaps of stretch along the bias - soft finished sail cloths have a reasonable amount - the better sailcloths have very little so will be unsuitable as Todd points out above.

Downside - there is little control over just WHERE the depth of the sal end up - it is all pretty vague and up to the attention of the sailor and the gods as to where the camber ends up. And as the breeze comes up the depth just keeps moving back - terrible for efficiency - the downside of the fabric's stretchiness.

3/ Sails with a combination of edge rounding and broadseaming.

The ultimate solution - not only is there control over how deep the sail is but the depth is placed where it is needed.

Sail performs well at all wind strengths (all being well!) and has maximum power for the area.

Because the broadseaming puts the depth close to where it needs to be, a less stretchy cloth can be used. This has the double benefit that the depth doesn't move around as much in different wind strengths as a softer cloth - giving excellent efficiency through the wind range.
_______________________________

It is great for people to try making their own sails - and do their own learning in this prepackaged, off-the-shelf world we live in.

It is really important to understand the general principles of sailmaking to allow a person to make an intelligent decision as to which direction they go in.

If they have just whipped up a boat over a couple of weekends from exterior ply it may be worth their while to whip up a polytarp sail with edge rounding but no broadseaming.

If they own a more sophisticated boat it would be silly to take make the same decision. The boat would badly underperform and the greater power of the various sail controls would probably rip the sail to bits or stretch it beyond useful limits. Good quality fabrics and broadseaming recommended.

However if the the person with the exterior ply boat wants to make the best possible sail for themselves it should be broadseamed too.

One area where there is no real way to skimp is with the detailing of the sail structure. Corner patches and tabling along the edges and good quality eyelets in the corners (and for any lacings along spars) will make any sail last much longer than otherwise - and this is one of the areas that people skimp badly in when making homemade sails.
______________________________

Here are some short videos of some sails with luff rounding only on a couple of PD Racers (puddleduck racers - about the simplest racing boat you can build)

http://www.vmix.com/members-mymedia.php?ID=29738

As you can see the boats are moving along nicely - but have very generous sailplans to compensate for the lesser camber - in the light wind pics the wind was around 5 to 7knots - not much - but the boats move well. However if you have a look at the stronger wind movies you can see that the sails are starting to distort quite badly - at least when the boat is sailing upwind - but still moving quite OK.

We have beefed up the mast a little bit since the vids were taken too! :-)
______________________________

Best Regards to All

And thanks again Todd for making such an excellent resource available.

Michael Storer

[Hwyl]

Another great thread, thank's Todd for the information (added to the Todd Bradshaw file).

Thanks Mik for putting it in a little perspective.

I'm toying with the idea of emulating your PD racer. I built a Frosty http://www.capecodfrosty.org/ a few years ago, but it got to be an arms race, the rules specifically said "the daggerboard shall be made of one piece of wood and not be reinforced by glass fiber" In my club, they took one board and sliced it into one inch strips reoriented the strips and laminated back together reinforced with carbon.

The PD racers you give a link to are too simple, but I like the ones you built.

[Saint]

What are the 'rules' about camber for jibs? I see some examples of negative camber on the luff and leach and possitive camber on the foot. How do I know what amount to give it when I don't have a spar to bend?

[SFC Hall]

check this one...

http://blog.modernmechanix.com/2006/06/05/latest-boating-sport-sailing-midget-ships/

[Tom Robb]

The bent spar would be the luff rope and the amount of bend depends on backstay tension. To make it non-bent/straight the backstay tension must be infinite. Obviously not a likely prospect.
Here's where your friendly expert sailmaker would be handy.

[PVanderwaart]

Todd, I'm not a sailmaker (except for one suit of polytarp sails for a Folding Schooner), but I would make a couple comments in explanation. First, the triangle theory is all about shaping the sail using darts (in lieu of broadseams) in conjunction with some rounding of the luff and foot, not about making a sail with rounding only. Second, the polytarp material is quite stretchy and the draft moves aft quite a bit in any real breeze. Third, there is a theory out there, propagated by Dan Segal and Phil Bolger, that a cat sail needs more draft, further forward, than a sloop main. So there was some basis for what was written. Incidently, when I built the sails mentioned, I used the factory-finished edge for the leech.

[Todd Bradshaw]

Saint, jib draft is created by adding a percentage of chord width to create luff round and positioned by broadseaming, very similarly to the way it's done on a mainsail. Here again, flare at the end of the broadseams is used to shape the entry angle, which is important since the sail isn't hiding behind a big fat mast.

At the same time, we have to figure in luff sag, since wires don't stay straight in use. This is typically on the order of about 1" of sag for each 10' of luff. After the round is figured and added in for draft, the sag amounts are deducted from that (full sag, mid-luff and about 75% of that figure at the 1/4 and 3/4 height chords) and the luff curve is re-drawn in it's final version containing both added draft and deducted sag. Due to the fact that jibs are skinny up top and wide down below, the final luff curve is usually "S"-shaped, with a slightly hollowed upper luff and a convex round on the lower luff.

PV, my "theory" on the triangle "theory" is that it's not a theory at all. It's a rather crude means of shaping a hunk of fabric, home-brewed by somebody who didn't know how to cut and shape a sail and was too lazy to learn. There is nothing about polytarp that requires this method over the proper method and no gain to be made by using it. The resulting sail and it's shape are crude and don't even take advantage of the limited strength and stretch-resistance that the material has to offer. Positioning the fabric with it's weave off-axis, just to be able to use a factory heat-sealed edge for a leech, to avoid having to make a simple leech hem makes no sense at all and just makes things worse. Leeches (or sections of them depending on the sail) should be hollowed to prevent flapping, not straight like a tarp's edge. There isn't a sail fabric made at any price which is so stable that this doesn't need to be considered and as I said above, proper orientation of the cloth to the stress is one of the most important principles in sailmaking. To ignore it when working with any type of material is just nuts. With an economy fabric which already has mediocre stability, it's doubly so and to do it to get out of the simple job of cutting and hemming a proper leech is off the scale.

The catboat sail draft "theory" has been around a lot longer than Bolger or Segal. Due to their stubby nature, catboats (as well as other wide hulls) can use deeper draft sails to help power them through chop and having no headsail the draft can be moved forward a bit. These things are common practice and have been for much longer than those guys have been alive. They are also very easy mods to make while doing the standard draft/luff-curve/broadseaming techniques, which will do it in a much smoother and more predictable manner than the "triangle theory" and a bunch of lumpy darts.

Believe me, I have nothing against people making their own sails. I have nothing against people using alternative materials, if they'll do the intended job safely. I even have nothing against using quick and dirty construction and design methods if they save time and money and get the job done properly, but these alternative methods don't save time, don't save money and clearly don't do the job properly when compared to simply using the proven methods. The "triangle theory" has all the earmarks of some engineer who thought he could figure out how sails are shaped without bothering to do his homework and find out how it's really done. The results speak for themselves to anybody who knows sailmaking. Why you people continue to support these folks and they're substandard building and design methods just baffles me? For about the same amount of time, money and effort you could build a real sail, even if it started it's life as a tarp.

[merlinron]

todd, again thanks for all the info, i now know about 100% more about how sails are designed than i knew before your post.
your comparison of cross-cut and vertical-cut broadseaming made wonder if one is more suited to different gaff angles than the other.
my sail is almost(actually, by angular definition, is) a gunter. peak is only 1.8'+/- aft the extended luff-line, as i said, very highly peaked. with this in mind, and considering that salrite's narrowest listed material is 3 ft. wide, which means that there aren't a whole lot of seams to shape with in either direction, am i better off with a cross-cut, and the resultant, "closer to a marconi" broadseam referance line profile(?)....vrs. the verticle-cut broadseam referance profile.
cross-cut gives me 6 seams in the height of the sail, vertical results in only 3 on the foot, of which carry up to; one about 4'-6" up the luff from the tack, and two on the head,(one about 10 inches past the throat and one about 2/3 up the head to the peak).... not allot to shape with. does Marino's book address this issue of shaping considering seam orientation and frequency on different gaff peak angles.
one thing that makes me think the cross-cut sail might be problematic, or hard to get decent draft shape out of, is that the entire sweep of the referance line ends up being almost vertical with very little curve in the top half as it passes the throat and aproaches the head, unless it gets very close to the luff in the throat area and along the upper third or so, of the luff. i'm thinking too close, there... the draft may end up too far forward(?), or, if i pull those seams in only enough to keep the draft back further,i will lose room to get some rounding. only about 12-14 inches of broad seem length for the 2cd, 3rd and 4th seams (4th seam is 1st seam on head above throat) . the upper(gaff) luff broadseam lengths suffer similarilly,although towards the top, obviously, the sail narrows enough that they might be ok.mainsail dimensions are foot 9.5, luff 10.25', head 11.76', leech 21.88', boom/mast 85 deg., peak 1.8' aft extended luff line.
maybe it will be ok, more or less like a marconi type profile with the high peak sail.
i have a basic understanding and visual conception of how broadseaming, flairing and other manipulations shape material.... i grew up with three older sisters and a mother that lived in front of a sewing machine. some of it actually rubbed of on me.

[Todd Bradshaw]

There are plenty more wrenches to throw into the works when you get to a complex design where small factors may improve or impede performance. Decades ago, cross-cut construction proved to be superior to vertical construction from an aerodynamic standpoint, since it tends to put the seams parallel to the wind passing over the sail and tends to make a smoother shape. It also allowed roached leeches to extend sail area and as a result, most modern fabric is actually woven to be most stable and efficient on a cross-cut orientation. Vertical cuts these days are still quite common and as a rule work fine, but it's done more for the cosmetic look than anything else. Some traditional sails just don't look right in a cross-cut, but if you had to make the absolutely best-performing sail for a given application and get to choose between the two types, cross-cut will likely get the nod. Then again, a five-second lapse in concentration on the part of a skipper on a race course can probably lose any gain due to sail cut, so everything is relative.

Other than the luff round which is in the process of tapering out up high, a Marconi main is cut flat for about the top third and just gets most of it's draft from wind pressure. A very high peaked gaff or gunter will likely be as well, so your broadseaming should be pretty much done be the time you start getting much past the throat.

One-off gaff sails always seem to be a bit of a gamble because of the complexity of the sail/spars/halyards relationships, so it's hard to be very specific about a particular sail without actually getting deep into building it. For most of us who don't use computer programs to shape sails it's pretty safe to assume that much of the shaping would be based on experience and a series of educated guesses or hunches. After a few years, you do get a feel for some of this and once in a while I'll look at one during seam basting and decide that I seem to be building in too much draft with the broadseams, or that maybe this particular area is too flat and I'll adjust on the fly. All of the canoe and dinghy sails that I've built over the last four years or so were shaped by eye alone. The perimeter for the lofting was measured, but all the rounds, broadseam curves and shaping was done without measuring or calculating anything. Unfortunately, by the time you get to that point, your knees are about shot and you're ready to hang it up and think about get back in the rock and roll business, because at least you get to sit in a chair or stand upright.

To build a complex gaff sail yourself is do-able, but it's quite tricky to get it right the first time and post-finishing shape adjustments usually involve a lot of de-construction, just to get at the part you need to alter to make corrections. It's a case where the Sailrite computer plotter could be your best friend. It will build the sail to extreme accuracy in it's little mechanical brain before it cuts any cloth. You'll still have plenty of work to do, but the guesswork is over before you even get the box in the mail.

[merlinron]

makes sence to me todd.
i have allot of time before i have to really worry about sails, i just like to think and plan as far ahead as i can. sailrite's computer sounds like the way to go...i'm quite sure in this area, money spent for thier design service is well worth it. my most educated guess, here, doesn't approach a shot in the dark! this thread came up at just the right time, as i just finished a more or less final sail plan, so i thought i'd ask some questions that were rattling around in my head....you have answered/advised to them way more completely than i ever expected.
i surely do appreciate all the information you have bestowed on us rookies.
ron ward

[bionicon]

>>>>>>>>>>>>>
Here's the file: Note that the illustration pages generally follow the text pages and unlike a book where you can read text and see drawings on the next page at the same time, you may want to occasionally scroll ahead to see the drawings on the next page as you go through the text.

http://webpages.charter.net/tbradshaw/!POLY-LA.PDF

Hi Todd.

I cant find your file. Is it still available?
I'm going to make a lightwind sail for our Tiki21. A G-0. Gennua or Windseeker out of light Tyvek or Polytarp.

The only thing I'm missing are the.

/Gunnar

[Todd Bradshaw]

I stuck it back up, so try the link again. If you want to save a copy, then download it now (it's a small PDF file - 24K) because stuff gets rotated in and out of that site pretty regularly due to space limitations.

[switters]

thank you, I don't post up here much because I am in the learning stage, but i read a lot. The PDf and the discussion on this thread is priceless and just in time.

Thanks again.

[Todd Bradshaw]

We're all still in the learning stage. It never goes away. That's part of the fun (and occasionally part of the frustration) of this whole process.

[sailing canoe]

It continues to amaze me, how open and helpfull the experts in our boat field are. Big thanks to Todd and others - Nick

[switters]

Dacron on order: check
pdf of building sail: check, thanks Todd
other sail making tutorials: check
permission to destroy GFs sewing machine: check
grommet puncher: uh oh

so the duck place I get my stuff from has grommets and those looked reasonably priced. And then I looked at the grommet tool and choked.

Are the two large pieces of metal worth it for two sails? Is there an alternative? If I buy them would someone want to share, assuming shipping cost isn't out of control?

[Thorne]

Dunno about the 'duck place', but sailmaking grommets are different from the run-of-the-mill brass grommets you find at hardware and craft stores.
http://www.duckworksbbs.com/sailmaking/grommets/CHG_B&N_2&4-big.jpg

I ordered my grommets and the expensive grommet set from the good folks at Duckworks -- well worth it, and I've since gone through nearly another bag o' grommets. They will buy it back for $5 less, suchadeal...

http://www.duckworksbbs.com/sailmaking/grommets/index.htm
http://www.duckworksbbs.com/sailmaking/grom_tool/index.htm

An alternate would be getting the grommets and tools from www.sailrite.com
http://www.sailrite.com/Categories/Grommet-Tools

[switters]

Thanks, those are the ones, just wanted to make sure someone had used them an they worked as advertised.

So what did you use to cut the holes with?

[Thorne]

scissors -- but one of the hole punches would have made life immeasurably easier...

[Todd Bradshaw]

You can usually get the hole punchers at a local hardware store pretty cheap or make them. I have a 1" hole punch made from an extra bit of steel tubing cut off of a Yakima roof rack and sharpened on one end on the grinder. Whack it with a 2x4 so you don't tear up a good mallet and you're good to go. Not elegant, but it works fine. Most of my store-bought punches were under $5.

I hear you on the pricing for the grommet setters, although the new generation of spur grommet setting tools are actually much cheaper than they used to be. I paid around $100 each for most of my grommet and eyelet setters and when you start adding up a whole bunch of different sizes, it gets pretty steep. It's hard to believe that this pile of simple little tools cost me over a thousand bucks.

http://webpages.charter.net/tbradshaw/setters%20copy.jpg

The rental deal works fine, but it's pretty handy to have at least one spur grommet tool on hand for projects. Sailrite currently sells their #2 spur grommet setters for $30. If I was going to buy only one size for everything from small boat sails to bags, covers, trampolines, etc, it would probably be the #2 size.

But, there are also other options. Sailrite's "Jiffy Grommets" aren't as traditional or quite as strong, but only cost $4 each and all you need is a hammer to set them. Hobie Cat-style, riveted, triangular aluminum tack and clew plates are similar.A sturdy brass or stainless round ring or D-ring can be attached to the sail (at a small notch cut in the corner) with 2-3 strips of webbing 6"-8" long, middled at the ring and sandwiching the cloth. Most webbing isn't terribly stiff and sewing machine needles will penetrate it without a major problem. The tricky part is making sure that your machine will handle the extra thickness. Some will, some won't. On most machines there is a limit to how high the cloth thickness can force the presser foot before the upper tension mechanism releases and it starts skipping stitches and/or making bird's nests. Some machines will also trip on the needle due to the machine's feed dogs advancing the fabric before the needle has cleared all that thickness on its way up.

Another good possibility is to hand-sew a ring. You could probably sail most small boats for a few seasons without the normal metal eyelet pressed inside of the sewn ring to protect the stitching, but it will last much longer with the liner. I had a friend who was a plumber that used a hardware store pipe flaring tool and some small hunks of tubing to make his liners and they came out quite nice. Avoiding metal shackles and attaching the sheets and halyards directly to the rings or grommets seems to have a substantial advantage when it comes to the lifespan of the rings.

Sewn ring with brass liner pressed in to protect stitching. Sewing perfectly servicable rings isn't hard. Learning to also do it neatly takes a bit of practice.

http://webpages.charter.net/tbradshaw/corner%20detail%202%20copy.jpg

[kenjamin]

My wife and I sewed my boat's sails on her little Bernina home sewing machine from kits we got from Sailrite. The people there are very helpful, knowledgable, and can tailor a sail design to your wants or needs. In my case I wanted a fairly flat sail that could comfortably handle a stiff afternoon blow on the Gulf of Mexico. There was also the little complication that the mast was curved. I didn't like the first drawings they sent me from their computer but after some further discussion and new drawings, I got just what I wanted.

My wife and I had a blast sewing up the sails. I did the seam taping and she did most of the sewing although I was a large component of the sailcloth feeding system.:D

The folks at Sailrite know all the tricks for sewing sails at home and their little paperback books are a wealth of good practical information for getting the job done correctly. Their kits are very complete. The only thing I bought at the home center was some silicon lubricant to slicken up the thread. I'm very pleased with the sails on Xena but I'm still fine tuning the rig.

http://ford.physics.fsu.edu/Xena056.jpg

[norseman]

Nice!
I'm in the process of modifying my gaff sail.
Roping was too tight, not enough offset at the throat and peak too high.
This was my first gaff sail, it may not be a racing sail but I'm happy with it. Didn't use as machine either.

ps Todd and Marino's books are mandatory. I think sailmaking is the ultimate craft, perhaps even more satisfying than building a boat.

http://farm4.static.flickr.com/3282/2786797250_83fb28c40d.jpg

[Todd Bradshaw]

I guess you could call sailmaking satisfying, in kind of a frequently tedious fashion (though there are plenty of times when I call it something that probably shouldn't be printed here). It is nice though, to get a chance to essentially build part of far more boats than I'd ever be able to build on my own and to have it be a part that stands out pretty well in a cosmetic sense and can make a major contribution to the profile and style of the boat. I suppose the biggest downside is their somewhat limited lifespan. I can pretty well assume that within a maximum of maybe 15-20 years tops from the date I build my last sail, they could all be gone or at least so old that they need replacement. If you build a hull well, it's nice to imagine that somebody might still be using it 50, 75 or maybe even 100 years or more from now. That's a warm fuzzy feeling that sailmakers don't get to experience.

[obscured by clouds]

Todd.. any chance of re-upping the PDF you posted earlier [much earlier!]?

I'm going to be building a standing lug from polytarp [unless I decide to cut up one of the numerous genoas and mains I have] and would like to get it reasonably right and working as a 'testbed' before I consider going out and spending a shedload of money on a professionally built sail.
It will be a big sail at around 180sqft set on a 22' birdsmouth mast on an 18' hull... so there's potentially a load of power there that needs getting right.

any advice gratefully received.

BTW I had toyed with the idea of taking one of the genoas, and essentially cutting the head off to create a lugsail. Would this work or would the built in camber effectively give me a 'bag-o-shite' :D

[norseman]

Perhaps one reason I find it fascinating is the challenge in shaping the sail and the learning curve involved. Anyone can stitch a sail together.
And everyone told me to forget about doing it myself,except you Todd and a few others ;-)

[andrewe]

OBC, get yourself Marino´s book, or Todd´s (next on my list) and you will learn much. I did, and made my own sails for my first project. Cutting up a genoa will probably teach you a lot, on how not to do it. If a spare sail, a cheap lesson.
Norseman, yes, anybody can sew. But it is quite difficult to get nice seams with the volumes of material. And don´t let him underestimate the finishing required after the main seams are done. BTW, I take my hat off to you on that boat, a delight.
Todd, your posts on this forum show the fortitude of a saint. Much apreciated (and immensely educational)
Andrew

[norseman]

Andrew, true, but the difficult part in my opinion is the sail design and all the variables involved, not actual seaming. As Marino says himself, seaming is seaming.

That's why I would design from scratch, instead of ordering a kit. After all, when you have obtained all the measurements and entered them in a sail plan you're halfway there anyway.

[Todd Bradshaw]

O.B.C. The PDF is back up, though being for a sprit-boom sail, it's not an awful lot of help as lugs are usually shaped using different methods.

http://webpages.charter.net/tbradshaw/!POLY-LA.PDF

I'm not even sure whether a 180 sq. ft. standing lug is really a decent possibility in polytarp. In Dacron, it would be built with cloth in the 5.5 oz. to 8 oz. range, which is a heck of a lot more stable and more durable than polytarp fabric. The tension required to keep proper luff firmness on a lug is going to be putting a tremendous amount of strain on the fabric along the luff as well as any sort of tape, glue, stitching or whatever else is holding the various hunks of material together. Even on standing lugs as small as 45-50 square feet from four-ounce Dacron (which is substantially stronger, more stable and more durable than polytarp) I'll generally have a luff that's five layers thick for it's length and with the addition of the corner or reef patches it may end up being 8-10 layers thick at the ends of the luff. This is not overkill, it's how you build a lugsail that lasts. You could try to duplicate this multi-layered luff reinforcement with tarp cloth, but I'm not sure how it behaves in such a situation, or what the best way to laminate it is. I do know that stitching would not be a good bet as it has very poor stitch-holding power.

Generating adequate luff tension without destroying the sail in short order is likely to be your biggest problem. I'm curious - why is your mast so long? You would have to have an awfully tall and skinny lugsail to need that much mast height. Here is another PDF showing a pretty typical standing lugsail profile at 180 sq. ft. and on most hulls it would work fine with a mast that's about 19' long, or even less, depending on how high above the floorboards you want the sail's foot to be.

http://webpages.charter.net/tbradshaw/!STANDLU.PDF

Notice that the fabric panels are oriented to be square to the leech and that the luff is actually cut hollowed, rather than having luff round like the sprit-boom sail in the other PDF. Long-ish standing lug luffs tend to sag as a result of both their unsupported length, flying out in front of the mast, and the difficulty of generating sufficient luff tension. Sagging luffs create excessive draft and one good way to help fix that on a lug is to cut the luff hollowed a bit. This does require though, that the sail's draft be generated by other means. In this case, it's done by broadseaming the vertical panel seams inside the wedge-shaped areas marked in blue along the head and foot.

Even if you can solve the construction issues, you will still have a problem due to the lightweight nature of the tarp material for a sail of that type and size. I wouldn't really expect it to last very long. Cutting up old genoas is another possibilities, but once you start cutting up a sail it's often surprising how little usable yardage it produces in the shapes and sizes you need. In general, most of the seamed areas and sail edges will have some shaping sewn into them and far more often than not, it isn't the shape you need.

[Bill Lowe]

Thanks Todd, refreshing way to start the day.

[obscured by clouds]

thanks Todd. excellent food-for-thought.

the lug plan was taken from a conversion to a National 18 sailing dinghy called 'Surprise' [Classic Boat August 1999]. I'm also doing a similar job an an old '18' I obtained.

the dimensions are: leech 23'; luff 14'6"; foot 10'6"; head 12'6"
with a 5* slopeback on the luff. The mast is around 21' long [not 22 as I stated] and rakes back at around 12- 15*. It will be sited around 20" back fom the stem. The yard is attached at around 30% of it's length.

There are 4 full length battens positioned more or less perpendicular to the luff, each with reefing pennants. the lower one is directly above the clew, thus forming some sort of boom

There's a small mizzen mast right at the back to help balance the boat.

I had toyed with the idea of shortening the mast a little- to around 19 - 20' and lengthening the leech/yard somewhat to keep the area by making it a high peak lug. I daresay I could extend the foot somewhat instead, keeping the c of e down a bit. the tack would be kept at around a foot above the deckline to allow for vision and downhauling. The downhaul would also be adjustable fore and aft. The mast partners are around 24" above the mast step so in reality once youve taken off 36" or so then the mast wont be that overlong.

the original 'Surprise' sail was vertically cut with the narrow panels [18" wide] orientated along the leech.

The longevity of the polytarp is'nt an issue, the point was to see if worked, or could be made to work, and more importantly whether I liked the set up before I splashed out around a £1000+ on a 'proper' sail.

[NwBtBldr]

Todd Bradshaw - are those pdf files still available? I just tried the links and found that they were not operating. I'm about ready to make a set of polytarp sails using the information on the website in the posting by Saint. Now that I've seen your postings, I'd like to see the rest of the information.

[Woxbox]

Another idea on the grommets. I needed a bunch once in pair of trampolines I made for a trimaran. I took them to a local awning guy and he put heavy ones in for a very reasonable price.

[Todd Bradshaw]

PDF:
http://webpages.charter.net/tbradshaw/!POLY-LA.PDF

get it fast, because I'm really tight on space at the old web closet with other work at the moment and it may not be there very long.

Also keep in mind that it is about building a sprit-boom sail and only a portion of the design work will apply to other types. Nearly all of the fundamental principles will though - and at least it's real sailmaking as opposed to that crap that Michalak and the other polytarp people spew.

[David G]

Todd - Thanks. I snagged it this time around too.


"The greatest obstacle to discovery is not ignorance - it is the illusion of knowledge" -- Daniel J. Boorstin

[NwBtBldr]

Todd,

Thanks. Just downloaded it.

[Driver Mark]

Todd,
Thanks for making the info on sailmaking available. I down loaded the pdf on the sprit sail but the standlupdf. link did not work. Would it be possible for you to re-post that? The info in the other is very interesting. Being very much the beginner at boats, sails, etc. I fell into the trap. (bad info that looked good because I didn't know the difference.) Would really appreciate it if you could make that available again.
Thank you.
Mark

[Todd Bradshaw]

http://webpages.charter.net/tbradshaw/!STANDLU.PDF
Not a lot of design info on that one, but it does have proportions for a pretty nice lugsail that could be reduced for other sizes.

[Driver Mark]

Thanks Todd.
It does help a little, too late for the first sail, but gives some better guide lines for future projects.
Thanks again.
Mark

[tdem]

It seems I'm a it too late to still get the PDF's. Just thinking, if someone emails them to me I can host them on my website, plenty of space left. They sound like a great resource and it would be sad to see them lost. I would add them to this page (http://tdem.net63.net/boat/links/sail.html) all nice and highlighted with a big thanks to the author :-)

[woodspars]

Very helpful discussion, fellas.

I have been wondering - could a flat sail be forced into shape by an array of adjustable, full-length battens? Would said battens obviate the need for broad-seeming and luff-rounding? What sort of results could be achieved through a combination of luff-rounding and full-length battens?

Thanks to all.

[Todd Bradshaw]

"Would said battens obviate the need for broad-seeming and luff-rounding?"

Nope. The reason is that when you want to take a flat sheet of fabric, maintain it's perimeter shape, keep the edges (where it needs to stay flat to meet the spars) flat and build a hump in the middle, extra fabric is needed to cover the hump. That extra cloth has to come from somewhere. On a sail, you are usually looking at a fairly small amount of extra (2%-3% of the local chord width), but in order to make the hump and preserve the perimiter, it still needs to be added. That's where luff round, foot round and on 4-sided sails, head round come in. They give a controlled means of providing that little bit of extra cloth, and of gradually tapering the excess out at the ends where the corners are and the shape becomes flat-ish again.

Broadseams serve the function of helping to move this added excess away from the edges and put fabric into the area of the sail where the hump is desired. The two techniques (adding fabric in the form of round and broadseaming) working together, generate the proper shape without distorting the perimeter. Full battens can certainly reinforce the final shape and make it more rigid, but if your fabric is stable enough to hold its planned shape without stretching out of shape (which is pretty important for sailcloth) and you try to force it into a different shape with battens, the usual result is distortion and big creases. The battens may have the desired effect of allowing you to make minor adjustments in draft amount and draft placement (through careful tapering and/or batten tension) but they can't add fabric where none exists.

What the polytarp folks are usually doing is going about the process using their own, home-brewed method. Instead of rounding and broadseaming, they are transforming their flat panels into humped panels by cutting out wedges of "cloth" and taping the edges of the holes back together, making darts. This is fine if you want to make a polytarp skirt for your wife, but it makes a lousy sail. Darts are weak, they tend to join edges which have their weave and stability going different directions (which can cause transition problems if it's not planned very carefully, making wrinkles and hard spots in the shape) and darts also look like hell. The planning/design phase of laying out the darts is just as complex (and usually less predictable) than real sailmaking techniques. This is my biggest gripe with the tarpsters. They aren't saving you any brain-work and what they are teaching you makes an inferior product from a function standpoint.

[woodspars]

Thanks, Todd.

While we're on the topic - can you recommend any resources that deal specifically with the design of full-battened sails?

[Todd Bradshaw]

I can't think of any right off the top of my head, other than the mentions that you'll find in the normal sailmaking texts. Jim Grant has an interesting short article on Sailrite's website that deals with high-speed sails and discusses the use (and reasons for) full battens in those sails which is worth reading. Much of it will also relate to some extent to boats with more moderate speed potential and full-battened sails.

http://www.sailrite.com/High-Speed-Sails

[kenjamin]

To chime in on the use of full battens, I had to plead with Jeff Frank, the designer at Sailrite, to let me have full battens in my experimental sail for my birdwing mast, but he finally designed them in and I've been very happy with the result. My boat is a Caledonia Yawl with a hull speed of about six knots but I knew that most of my sailing on the Gulf of Mexico would be in the summer afternoons when the wind really kicks up. The tacks are quiet and sail feels to be under control even in gusty conditions probably due mostly to the increased mass of it with the full battens. Anyway, just wanted to say there are other reasons besides ultimate speed for having full battens in a sail. Another reason is that I just like the way they look.

http://ford.physics.fsu.edu/Xena056.jpg

[tdem]

They also make rolling up your sail after sailing a lot easier! You have a very nice boat, kenjamin. That mizzen is really clever!

(Maybe someone could email the pdf on sail design to me? My email is 106498@gmail.com. It's a weird number because I don't give my private email online to keep spam away. I would greatly appreciate it because I was going to make sails using the "bad" method but now I don't want to after reading this thread.)

[Todd Bradshaw]

Both PDFs are up at the moment and have been for a few days. Try them now.

http://webpages.charter.net/tbradshaw/!POLY-LA.PDF

http://webpages.charter.net/tbradshaw/!STANDLU.PDF

[kenjamin]

The mizzen mast, a Shaw and Teeney oar, was a fun experiment but it's not stiff enough to do the job properly or to depend on for serious sailing. I'll be gluing a new one up that will be still in the shape of an oar but it will be much stiffer and stronger. It may be a little longer so that it can function as a sweep off the stern. Like Janis Joplin sang, one thing you can say for me – I'm never satisfied. :D

http://ford.physics.fsu.edu/Xena088.jpg

[tdem]

That sail shape reminds me of a spitfire wing(Good aerodynamics there!). Has anyone here tried using the Sailcut CAD (http://www.sailcut.com/Sailcut_CAD) free software to design a sail? I played with it a couple of years ago but it has changed a lot. Maybe something for our more knowledgeable forum members to take for a "test drive".

ps: Todd, whenever I try to download your mirror seems to be down? Just my luck! I love your book about canoe rigs by the way. Got me thinking about what cool things sails can really be.

[tdem]

Does your webhost block people from New Zealand? I could only download the files through a proxy, feel like a hacker now. Anyway thank you so much! These are surely the ultimate polytarp sailmaking guides.

[Todd Bradshaw]

Not that I know of, but I'm pretty clueless about how internet sites work. We've been using the site to send songs and other stuff back and forth for the band and some of the guys can download things with no problems and others have trouble. Once in a while, my own web-space won't even let me in to change something and I have no idea what's up with that? For what it costs me (nothing) it's helpful, but is does behave rather curiously at times. Glad you managed to get them.

There is nothing in those files that isn't front and center in any decent sailmaking book (which makes the fact that most of it is missing from nearly all polytarp sailmaking instructions rather curious as well).

[andrewe]

Todd, nothing unusual about the alternative outfits and followers refusing to believe the obvious, and well documented mainstream. Much rather go for promises and alternative ideas that sound better than the boring experts. Seen a lot of that in medical matters.Crystals, aroma etc.
A

[keyhavenpotterer]

I have been trying out Sailcut4 to design and make a lug mainsail for my new Raid41. I have just posted on the build blog a page on the design with a link to the current final shape and also a link to the output from Sailcut4, in this example the foot panel. I would be grateful for feedback on my design, it is my first, although I have been racing with lug rigs for some years. Material will be Dacron roll ends from an eBay supplier (UK)

http://strathkanchris.wordpress.com/boats-i-have-built/trim-the-first-raid41/trims-rig-by-brian-pearson/

Brian

[obscured by clouds]

I'll be interested in your conclusions as I'm grappling with the same idea - but for a standing lug rather than a balanced.

My general dimensions are as follows:

the lug plan was taken from a conversion to a National 18 sailing dinghy called 'Surprise' [Classic Boat August 1999]. I'm also doing a similar job an an old '18' I obtained.

the dimensions are: leech 23'; luff 14'6"; foot 10'6"; head 12'6"
with a 5* slopeback on the luff. The mast is around 21' long [not 22 as I stated] and rakes back at around 12- 15*. It will be sited around 20" back fom the stem. The yard is attached at around 30% of it's length.

There are 4 full length battens positioned more or less perpendicular to the luff, each with reefing pennants. the lower one is directly above the clew, thus forming some sort of boom


extracted from an earlier post in this thread. i've been quaoted around £600 [$1200] for it to be made by a local sailmaker, but if I can have a go at making my own I can save a fair bit.

[Todd Bradshaw]

Hi Brian,
I haven't used such a program, but I'm a little surprised that if it was going to generate a cross-cut lugsail, that it wouldn't take advantage of a tack seam (the panel-to-panel seam which intersects the tack corner on a cross-cut sail is the most powerful sail-shaping spot on the entire sail and plays a very large part in generating the slightly cupped nature of the sail's bottom). In this case, the first seam has been moved upward on the plan (most likely to enable it to use a full-width bottom panel and save cloth) but the only possible shaping going on anywhere near the bottom of the sail is that lowest panel seam. It looks on the panel plot as if one of the two bottom panels is curved a bit along the seam line for shaping, but it's awfully high up to really do much for creating draft and shape in the lower 25%-30% of the sail - where the bulk of your sail area happens to be. There is also no shaping at all happening in the area of the foot round, which means that rather than forming a bit of cupping along the foot, the round will just be an unsupported flap, and flap it probably will (I'm assuming that the sail is loose-footed, since there is a lot of curve on the bottom and extra fabric for a hem is allowed in the panel plot). A lot of cross-cut sails actually have foot panels which have been split vertically near the middle and then reassembled with a bit of taper in the seams to generate the desired cupped shape along the bottom.

Will the program allow you to move the panel seams downward until the lowest seam is close to the tack corner? It would also (by the way) move the throat seam down, closer to the throat corner. This is another place that is a good spot for generating shape (but it needs to be done delicately and gradually, as throat corners usually won't set well if you build-in too much shape there). Unless the computer was instructed to design a sail which is nearly flat, or just a portion of a cylinder, rather than a cup, I'm surprised it didn't think of these things and I wonder where it thinks it's going to produce and position some draft.

Just holding a ruler up to my screen, I'm also seeing no round along the head and no allowance at all for bend in the yard. You certainly don't need a lot of head round up top (helps creat draft, which you only need a small amount of up there) but it's very unusual to have no round along that edge at all on a lug. Spar bend on small sails is a reality that can't be ignored and doing so usually results in a sail that's either too flat or in many cases, distorted.

Here is a mock-up of a typical lug building plan (not to any specific scale). It's done in traditional manner (broadseamed) rather than computer-style (panel-shaped). The difference between these two methods is actually all inside the areas where the seams exist. In traditional construction, we work with constant width panels (12", 18" or whatever) and generate shape by making adjustments in the seam overlaps between panels. You can actually look at one of these sails and see some of the seams get wider as they approach the edges. A seam that's 1/2" wide in the sail's middle can sometimes gradually broaden to as much as 1.5" at the edge of the sail.

Computers end up with the same sail shape, but do it differently. They keep the seam widths the same everywhere on the sail (faster and easier to sew with high-speed machines) and generate the shape by cutting the edges of the panels, themselves, into curves. Having all that mechanical brain power available greatly aids in figuring out exactly what these curved cuts should look like. The finished sail will have the same shape, draft, entry, etc. but the seams will be different between the two versions - one variable (traditional broadseamed) and one fixed-width (computer cut).

Anyway here is a typical lugsail plan. Notice that seams heve been moved to intersect near the tack and throat corners to aid in shaping the sail. The other luff broadseams are mostly there to position the draft properly and make a nice, controlled entry that's fairly round (reduces stalling and makes the sail more tolerant of steering/trimming errors). The foot panel is split vertically and broadseamed back together to help give the foot just a little bit of cupped-shape on the bottom. The leech is hollowed to prevent flapping and also built with a couple of very gradual, small broadseams to help keep it tight as the fabric ages. The head has a bit of round, and that round is further increased by adding allowance for the bend that the yard will have in use.

http://webpages.charter.net/tbradshaw/lug%20plan.jpg

Whether you build with constant-width cloth, sewn together with variable-width seams (broadseamed construction), or with constant-width seams, joining curved-edge panels (conputer-cut construction), these sail shaping factors (entry, hollow, draft placement, foot shape, spar bend, etc.) all need to be present and accounted for. The fact that you are using a computer to do the figuring does not change this, it just makes it easier and faster. The problem that I see with your plan is that as far as I can tell looking at a small version on my monitor, several of these important factors don't seem to be taken into account. It has generated what seems basically to be a section of a cylinder with a little bit of draft and entry modification.

As I said, I have not used the program and maybe it refines the plan and the shape of those panels at a later step, but I certainly would not start cutting fabric until I found out. If you have Marino's book and can follow directions, I would be willing to bet that you could cut a better lugsail using the book, a few strings and a tape measure. There is certainly nothing wrong with computer designed and cut sails. I've built a bunch of them and if I had the money to buy the proper equipment, I'd save myself (and my knees) a whole bunch of hassle. However, all the factors that turn flat fabric panels into a properly working airfoil still need to be accounted for.

[norseman]

Excellent. Todd, correct me if I'm wrong but a bit of hollow in the luff?

Here is Gartside's Riff sail made for a Færing,
http://farm4.static.flickr.com/3169/3067384056_6dd79d3a97.jpg

Keyhaven, how did you post the sailcut files?. I have a project ready to loft and would like to post the drawings here.

[Todd Bradshaw]

Luff shape on lugsails (straight, hollowed or with luff round) is sort of a "dealer's choice" issue. I usually cut them straight if they're pretty short and a little bit hollowed if they're longer. They get a lot of downhaul strain, so they need to be pretty well reinforced (roping or double-binding with luff tape). We're trying to create a stable leading edge, even though it's flying unsupported and all by itself out in front of the mast. We don't want them sagging inward because it creates unexpected draft, so a sturdy edge and high downhaul tension are pretty critical if you want good draft control.

Hollowing as a means of countering luff sag is similar to adjusting a jib luff for headstay sag. As luff tension pulls the hollowed edge straight, it subtracts excess draft caused by the sag. On smaller lugsails with short luffs, I'll generally double-bind them. This makes their luff edges at least five layers thick for their entire length and they will stand up to a lot of downhaul tension without stretching. As long as the downhaul is decent, I haven't found much reason to cut these little ones in any shape other than just straight. There just isn't enough luff length on small sails to sag much, and even 4 oz. Dacron is proportionally pretty stiff and stable when it's five layers thick.

A roped luff uses fewer layers of cloth, and is very strong, but it's somewhat less stable and a bit more likely to stretch under tension. I cut most of those with a little hollow on just about any sail, big or small. We know the luffs will tend to sag in use and we know that roped edges are a bit stretchy, so the hollow just helps counteract and fix any problems before they can even happen.

[keyhavenpotterer]

Terrific reply Todd. Thank you. I will spend more time absorbing all the details, but here is a quick reply on a couple of points.

Have not come across any way to move panels around as yet. Just enter all the numbers and out comes the drawing. I will try and arrange to post the actual numbers entered into the program on the Trim blog site. My very latest attempt does have some negative round in the luff. There is 30mm of gaff round in the numbers.

Output from the program was very difficult. The DXF output always seemed to be blank when read. However the simple print output worked ok, so Michael Storer kindly sent me a link to a free software that will take printer output and turn it into a PDF file. That finally meant I could post something.

http://www.pdfforge.org/products/pdfcreator


I do hope we can work together and work up a nice lug sail shape in Sailcut4. People could then just adapt the dimensions to their spars and out would pop the xy panels. Would help de-mistify the process.

Brian

[Boatmik]

Good stuff Todd!

Brian .. if you can establish a shape with the software I can eventually do drawings that move the cloth into economic position and also clarify the cartesian co-ordinates the program spits out so that mere mortals can grasp them.

One simplification would be to use a loose foot ... as yours will ostensibly be a racing boat. Gets rid of one broadseam even though it is a little one.

Todd, do you think it is OK to get rid of the foot broadseam? A lot of loose footed racing sails here don't have them and from memory haven't had them for a long time. The mainsail doesn't here. though the jib clearly does. (the boats have an over-rotating mast which is why the main seems excessively flat). Foot adjusted for different points of sail of course.

http://www.ns14.org/images/large/NSWState080138.jpg
from the NS14 website (http://www.ns14.org/gallery/index.html)

Cheers
Michael

[keyhavenpotterer]

Some numbers to try inputting into Sailcut4 so everyone can play along

currently I have entered into the program
gaff to suit your spar
leech -20mm round at 55%
foot 120mm round, plan to have it loose footed and gaff in a sleeve
luff -20mm as my current sail has negative luff when I looked
sailshape is set to 10% depth at all three levels, head, mid and foot
twist angle 10 deg
sheeting angle 12 deg

I too would value a discussion on broad seaming with a loose foot. My current lug sail is set in a track and has super depth. Seems it should still have shape which is adjusted with outhaul even if loose footed?

http://farm4.static.flickr.com/3200/2790553290_1d0ebbd921.jpg?v=0

Brian

[tdem]

If you read down from here (http://sailcut.sourceforge.net/docs/en/#id325806) it explains how sailcut does the shaping. I have to say the maths behind it makes my head spin! Further down it explains the file formats.

Why would someone use a -not loose- foot anyway? Most of the racing dinghy's I sail have a loose footed mainsail and I really havn't noticed any difference in performance between the two types. Loose footed ones are certainly a bit simpler to rig.

[norseman]

In Sailcut open the file, go to "shaded view"(for example),"view" in the top menu,"dimensions",bottom left in the dimensions window.
Enter vertical cut ,cross cut or whatever.
Click OK and Bob's your uncle. ;-)

[Todd Bradshaw]

The need for the foot broadseam (or not) is usually a function of how much foot round you are trying to support. If you keep the round fairly modest, you may be able to get away with just a single panel. Once you get to a certain point though, the round will start to flap and you will find that you have no way to tension it to stop the flapping. This is because the line of tension that stabilizes it is a straight line between the tack grommet and the clew grommet. The more you tension the outhaul, the more tension you create along this line and the greater the tension difference becomes between that line and the fabric immediately below it (the foot round). A modest round will usually hold its shape up to reasonably high tension. A bigger round usually won't, and is a good candidate for the broadseam to give it a bit of cupped shape (which essentially makes the panel slightly shorter, right along it's bottom edge). Foot round shape and amount on loose-footed sails is largely an aesthetic choice for the designer. Straight-cut sail feet look very crude, even though they might work just fine. I don't really believe anybody has ever claimed that their extrordinary boatspeed was a result of the shape and depth of their foot round.

You also have to keep in mind that different fabrics exhibit a broad range of stiffness and bias stability. Three inches of round might work great with one fabric for a specific design and flap like crazy with another cloth that was less stable, or which had softened up a lot from age. This factor also needs to be considered when broadseaming anywhere on the sail. Stiffer, more stable Dacron may need up to twice as much broadseaming to generate a specific in-use sail shape as a soft grade of Dacron. This is just another one of those factors that you have to keep in mind when you design a sail and might be something that could be a problem for any sort of "universal design application" that folks could apply to any similar sail. In the case of the computer-sail, it wouldn't be a question of broadseaming amounts, but it would certainly have a similar effect on the panel-shaping and really can't be ignored.

The advantages of connecting the foot along the boom, rather than going loose-footed, are generally that in some cases, it can in make sail handling (raising, lowering, furling, etc.) easier, and the other is called the "end-plate effect". In a nutshell, this says that a certain amount of your wind pressure on a sail leaks out under the foot and escapes without giving you much benefit - and/or helping to maintain the difference in pressure between the windward and leeward sides of your airfoil, reducing your lift. Building kind of a shelf at the bottom (or the top if you can figure out how to do it ) helps prevent this leakage, increasing efficiency.

This was a considered a very big deal on racing boats around 20 years ago and sails often had a panel connecting the sail to the boom that was soft cloth, airfoil-shaped and nearly horizontal when in use. Some even had zippers and other gizmos that were installed in them for control over the draft and depth of these shelf feet. This trend seems to have died down considerably since then, in favor of building a more moderate, less horizontal shelf and making it from the same cloth as the rest of the sail, with merely a bit of heavy-duty shaping on the lower sail panel(s). The idea is that the sail attached to the boom is forming your end-plate to prevent leakage, but since tacking an airfoil of cloth to a straight boom would tend to mess up the airfoil well up into the body of the sail, that 3-D shaped lower panel helps carry your good airfoil shape down closer to the sail's bottom without distorting it.

The photo Brian posted above is such a sail. The traditional construction method used to build the foot on a sail like Brian's is pretty interesting. You essentially lay out your plan as if it would be a loose-footed sail, complete with a pretty healthy foot round on the bottom. This generates a bottom panel which is pretty straight along it's top edge (to meet the panel above it) and which has a fairly deep curve on its bottom (the foot round). You cut it to that shape, but leave some excess fabric at the front and back ends of the panel. Then you attach this foot panel to the rest of the sail - but you attach it upside-down! You sew the big "foot round" curved edge to straight bottom edge of the panel above and the straight-ish edge ( that had been the top edge top in the plan) becomes a straight foot, where you will eventually attach the boltrope to slide onto the boom. Then you get out a batten and cut the ends of this upside-down bottom panel to match the luff and leech curves of the rest of the sail. You now have a sailshape that carries its draft almost all the way down to the boom without distortion, but is connected to a straight spar and forms an end-plate down there to help prevent leakage.

When I was first learning to make sails, I must have read the paragraph in the book 50 times, trying to figure out why on earth I would want to draw and cut the panel to fit the plan - and then sew it on upside-down? But after doing one, it all finally became clear.

[keyhavenpotterer]

Thanks so much Todd. Think you have talked me into staying loose footed! How about the head. Most lugs are tied on to the spar, my current boat has an extruded plastic track glued with Sikoflex to the spar - an expensive solution. have been planning on sleeve with small cut out for halyard. Might also allow for sleeve replacement if there were problems with shape and setting .

Although Sailcut4 allows different panel layouts, still not clear how to adjust downwards the panels so that the first seem goes into the corner.

If I followed your lovely design from above posting, can I check with you how you actually go about sewing the broad seam. Say I want a 30mm broad seem at the tack panel. Do I lay the two panels 30mm plus minimum seam wanted over each other, begin sewing from the leach in the middle of the seam, and as I approach the tack move the two panels gradually apart as I sew and have them 30mm apart ( still with min overlap) by the tack?

Thanks, Brian

[norseman]

Can't help you there keyhaven,it's fun to play with the program but I will draw it traditionally as Todd describes. No luck with posting pdf's except links to a web.

[Todd Bradshaw]

A sleeve on the yard will work and they are nicely clean from an aerodynamic standpoint. What they sometimes lack is adjustability, so you have to be pretty sure that the small cut-out is in the right place. The vast majority of the tension along the head should be on the corners, rather than along its length, so you might want to make a fairly generous halyard cut-out to give yourself a little room for experimentation. Does it truly work better or make the sail set better than a batch of lacing grommets? Most likely not, but if nothing else it might eliminate the need for another rather expensive grommet setter.

For the broadseam, standard procedure would be to start sewing at the leech with whatever your standard seam overlap is (1/2"-5/8" is typical) and hold that width until you have proceeded far enough forward to reach your pre-determined broadseam curve. Then you gradually start increasing the panel-to-panel overlap as you head toward the luff edge. Over the last few inches, you increase your overlap at a slightly higher rate. This adds a bit of final flare to the broadseam and helps give a more rounded entry to the sail, which helps reduce stalling. So if, for example, your standard seam was 10 mm wide, by the time you get to the luff and add a 30 mm broadseam, the seam width would be 40 mm at the luff with the increase in width spread over several feet of seam. How much you broadseam a particular seam depends on how firm or soft your cloth is (firmer cloth needs more broadseaming due to having more bias-stability and less stretch) and it also depends on how many seams you have available to help shape the sail. A sail with 36" wide panels will have fewer seams to work with and subsequently more dramatic broadseams than one made from 12" wide panels, where the same amount of broadseaming can be accomplished with smaller broadseams but more of them.

Here is a photo where I have marked the approximate broadseam curve with red lines. If you look carefully, you can see the seams to the right of these marks (between the curve and the luff and foot edges) slowly grow wider as they approach the edge.

http://webpages.charter.net/tbradshaw/broadseams.jpg

The mainsail below is loose-footed and has a fair amount of foot roach. The tack seam is broadened, but so is the lower 12" or so of the panel seam that you see striking the foot about half-way between the tack and clew. This broadseam is what gives the sail's bottom that little bit of cup-shape, preventing the foot roach from just flapping in the wind and and also creating at least a small amount of end-plate down there. Who says you can't have a mast made from maple and use cheap screwdrivers for tack downhauls?

http://webpages.charter.net/tbradshaw/salt%20bay%20skiff%20019.jpg

[keyhavenpotterer]

What a great picture. Have to give way to the tree at the mark rounding, it's on starboard anyway. Thanks again Todd, tremendous help in understanding broad seaming. Ordered your lovely book this afternoon - Christmas treat for myself.

Brian

[keyhavenpotterer]

Have been trying to use Sailcut4 and put a seam into the tack. Only way I managed was to design the sail as a radial layout. Out came a very racy looking lug sail. I will try and add the pdf drawing to this post and also to the building / rig blog for RAID41.
Cannot manage the pdf here, same as others I think. will attempt to add to blog

Have added it to Michael's forum here, post 254

http://www.woodworkforums.com/showthread.php?t=74360&page=17

have also added a nice looking narrow panel vertical cut lug mainsail two posts down. this has seams into the gaff/luff corner.

Have also managed to update the Trim blog with a brief note on broadseaming. Have added two images accredited to Todd and posted two pdf's of the radial and vertical versions of the same Sailcut4 sail.
http://strathkanchris.wordpress.com/boats-i-have-built/trim-the-first-raid41/trims-rig-by-brian-pearson/learning-about-sail-broadseaming/

[Todd Bradshaw]

The radial is kind of cool, although there are a couple things that bug me about the layout. The whole deal with radials is using the stability and stretch-resistance of the weave (the warp yarns, in particular) to your advantage in creating the most stable cloth airfoil possible. They allow you to aim those yarns straight up and down any edge or area that is under a lot of tension and to a large extent (at least on small and medium-sized sails) the shape you build is the shape you get and normal rigging tensions aren't going to do much at all to change that shape. Here is your plan, and really, the idea of a radial lugsail isn't all that crazy as long as you have a means to plot the pieces and develop the shape (a lot of those straight panel lines are actually curves on the real sail and it pretty much takes a computer to determine what those curves should look like). Radials also waste a lot of fabric because panels are plotted with weave direction in mind, not fabric economy. This is critical to the finished sail's performance, but yields a lot of expensive scrap. This is why big sail lofts make and sell fancy Kevlar tote bags. They are using up small bits of left over cloth to get back some of the cost, and also making sure sewers have something to do in their down-time (unlike me - I spend my down time cruising boating forums and playing my guitars - it doesn't pay as well, but sure beats the heck out of making tote bags :))

http://webpages.charter.net/tbradshaw/rl.jpg

OK, the foot and bottom on your plan look great and would be solid as a rock. The leech and luff are equally quite good. My problem is the layout along the head. With a standard thread-line orientation, the warp yarns along the head would all be running pretty close to vertical. This is not really all that different from a typical vertically-cut lug's head, but it does leave the cloth along the head edge cut on a pretty steep bias, which is the least stretch-resistant way to cut any piece of fabric. In this case, you have created very stretch-resistant panels along the luff, foot and leech and you are mixing them with a head that may stretch like crazy by comparison. Three edges of the sail are now quite predictable in terms of stability and one is quite unpredictable. How hard can we tighten the peak outhaul before the top starts to distort or how long will the sail last before stretch along that one edge starts to take it's toll on our designed sail shape? We don't know these things and even with exotic fabric, the stability difference between stress placed on the warp yarns and stress placed on a bias-cut edge is going to be big.

I would rather see a radial lugsail cut something like this.

http://webpages.charter.net/tbradshaw/!RADIALL.jpg

Notice that all edges have the cloth weave adjusted to reinforce and stabilize that edge, yet if you look at all those little arrows, there is a very clean flow of warp yarns throughout the sail with the smoothest possible transitions from panel to panel. Radials are all about smooth transitions and matching the flow to the stresses. Since we're spending your money, I gave you a Kevlar leech for more stability and durability. As long as the flow is good, you can do this sort of fabric mixing on radial sails to add extra beef in the way of heavier cloth, or even a different cloth in high-stress areas, and/or lighter cloth in low-stress areas.

If your computer will allow you to figure out a radial in only three sections (tack corner, clew corner and the top) you could go one better and plot the lugsail like this.

http://webpages.charter.net/tbradshaw/L2.jpg

We maintain a horizontal seam at throat level, which essentially allows us to build-in what would be the panel-shaping equal to a slight throat broadseam to shape that area, and we have the option for a slight leech broadseam at the aft end of the same seam to snug up the leech shape. Traditional, it's not..... but this would be an extremely smooth sail and most likely stay that way for a very long time. How far-fetched is the idea?......... This is the first radial I ever built and we've been using it on our Sunfish for about 25 years now. It gets babied and is never left out in the weather, but the shape is holding up beautifully (notice the sleeves along the yard and boom - I always hated those nasty little plastic hoops).

http://webpages.charter.net/tbradshaw/sf%20radial.jpg

[keyhavenpotterer]

Michael Storer did not like "my" head either, will just have to try harder. What fun! Have just tried a number of changes to the radial setting and at the moment cannot make a radial head with any of the options.

Brian

[Boatmik]

Thanks so much Todd. Think you have talked me into staying loose footed! How about the head. Most lugs are tied on to the spar, my current boat has an extruded plastic track glued with Sikoflex to the spar - an expensive solution. have been planning on sleeve with small cut out for halyard. Might also allow for sleeve replacement if there were problems with shape and setting .

Thanks, Brian

Remember that if doing a sleeve over the spar the spar taper will reduce the effective round with the result the sail is flatter than expected.

So for sleeves on a yard or a gaff the taper probably needs to be taken into account. Maybe calculate it as the differences in the half circumference compared to the smallest part of the spar.

With sails attached to masts the taper is so long it is probably not warranted to make a correction.

Best wishes
Michael

[Todd Bradshaw]

As long as we're introducing miracle materials to our lugsail for increased stability and durability, we might as well add one more piece. We substitute another hunk of Kevlar in the tack assembly and make what is known as a "Tack Spike". This is just a reinforcement that helps our sail hold it's shape a little better over time by adding a band of our extra stable cloth leading from the tack corner up through the middle of the sail, fairly close to where we have our maximum draft (and want it to stay).

http://webpages.charter.net/tbradshaw/!TACKSPI.jpg

I suppose that on a lugsail you could also make a case for similar reinforcement along the luff, though a typically well reinforced lug luff is already pretty stable and likely may not need it.

Your vertical-cut lugsail plan looks pretty good. These are actually the easiest to make and the most common. The broadseaming is very straightforward. The seams that happen to pass through the red triangular marks on the top and bottom of the sail in this photo are the ones that get broadseams. Broadseaming starts when the regular seams, coming from the middle, reach the marks and the panel overlaps increase as the seams near the foot or head edges. On a sail with that many panels, the increase is usually 1/2" or less per seam within the foot area and about half of that on the head seams.
http://webpages.charter.net/tbradshaw/standing%20lug%201%20copy.jpg

[Boatmik]

Yes .. looks cool!

But I guess it begs the question ... Warp oriented sails are used on boats with high rigging tensions and adjustment tensions.

In the good old days we used 2:1 cunninghams to tension the sail luff even on quite big boats.

Now it is all 8:1, 12:1 or running to winches.

We really didn't use the cunningham to bend the mast as they do now on lots of classes.

This all assumes stiff sails, stiff spars and stiff necked crew.

Lugs tend to have a genteel floppiness. Are the fancy cuts warranted?

Certainly trying to achieve tricky things with software is a way of learning to use it VERY effectively.

Note too the pic of the NS14 I put on the previous page which I was using to demonstrate no foot broadseaming.

This is a high tension sail of the ultimate kind ... but no fancy layouts. It is a laminated cloth though.

If a warp oriented lug was put together you would certainly learn a lot about designing and sailmaking.

And posting the idea brings more gems out from Todd. Who is putting some time into this - thanks hugely Todd!

So ... really ... I have no reason to complain!

Michael

[keyhavenpotterer]

So that you may take a look at how each vertical panel looks when Sailcut4 outputs them, I have posted a PDF on the blog. Will have to learn how to do it here.

The new file is at the end of the post.

http://strathkanchris.wordpress.com/boats-i-have-built/trim-the-first-raid41/trims-rig-by-brian-pearson/learning-about-sail-broadseaming/

[norseman]

Thanks everyone,very interesting thread. But I have to agree with Boatmik,are the fancy cuts warranted?
Just like model airplanes, start with something simple.A nice vertically cut lug from soft dacron I say. Hand stitched.Especially for something like the boat in question;

http://strathkanchris.files.wordpress.com/2008/11/2975445897_271b628d86_o.jpg

[Todd Bradshaw]

Michael, though the NS14 main has no traditional broadseams, I think that being made of five seperate chunks of mylar, it's pretty unlikely that the bottom panel was made flat and it's very likely panel-shaped to do the job, instead. It's also showing a slight crease across the foot roach, starting at the tack - meaning that with this sort of wind and outhaul load, it could have used a bit more shape down there. How it sets at lighter loads might be a different story and as always, everything in sailing seems to be some sort of compromise - sometimes it's nearly perfect, other times, not so much.

As to whether the high-tech cuts on simple sails are warranted? I would say that they are certainly justifiable from a performance standpoint. In terms of using the characteristics and strengths of the material to your best advantage for a smooth, long-lasting shape with minimal weight and maximum strength, they are hard to beat. Whether or not they are necessary or whether or not the extra expense is worth the increase in performance over a well-built, regular sail is a different question. If I had to class race my Sunfish and they looked the other way when measuring and checking the sails, I'd take my radial over anything the manufacturer ever built in a heartbeat (my boom vang, too, but that's another story). It simply has better shape, holds that shape better and is a more efficient airfoil. On the other hand, if I had my druthers, my Sunfish would be a beautifully restored old woodie and I'd build the sail with a vertical cut and 8" false-seamed panels from a lovely grade of cream-colored egyptian cotton and I wouldn't care if I got beat in a race. Since very few people these days actually need to go sailing, it should do for you whatever it is that you need it to do for you and the definition of what makes a really beautiful sail should fit its owners desires. So, I think there is room out on the pond for both the guy who builds a nice traditional lugsail and the guy who wants to take a more high-tech approach. I would, however, like to see each of them done well as I see no excuse for an ugly boat, or an ugly sail and last time I looked, the definition of the word "prototype" did not include an allowance for shoddy work.

I do, personally, draw the line when it comes to hand-seaming on Dacron. I've sewn enough by hand over the years that I'm decent at it and I have no doubts that I can make a stronger, flatter, smoother seam with my machine. The thin, hard nature of Dacron just doesn't allow stitches to snug down into the cloth the way cotton does and the tearing properties of Dacron don't go too well with lines of big needle holes. Of the various bits of traditional sailmaking methods and technology that can be translated into modern materials, hand seaming is one that I don't think makes the jump to lightspeed too well. The finished result usually has neither the look of cotton technology or of Dacron technology. There was a photo posted a few years ago on the forum of a big, fancy boat on a WB cover. We all spent about three days trying to figure out why the sails showed puckering along all the seams on such an obviously expensive boat. It turned out that they were all hand-stitched, and by Ratsey and Lapthorn at that - who are certainly top notch when it comes to hand work. I'm sure those sails cost a bundle and I can certainly respect the craftsmanship and the monumental job it was to sew them all by hand, but to my eye, they missed the mark. That part of the construction process just didn't translate well into the modern material and the result was far more distracting than it would have been to machine-sew the seams and then save the hand work for the trim (rings, cringles, roping, etc.). Your mileage may vary.

[keyhavenpotterer]

Agree completely that a vertical cut sail will look very nice and suit the boat. Vertical panels will be my opening attempt. May even try alternative panels in a different colour. Nice to stand out I feel! The small cuddy is a signature bit and a nice two colour vertical sail could be another. What colour might look good? Just cream, just tan?

Have added a screen dump from Sailcut4 to show how it might look and also with the sail rotated to show the shape.

http://strathkanchris.wordpress.com/boats-i-have-built/trim-the-first-raid41/trims-rig-by-brian-pearson/learning-about-sail-broadseaming/

Also, since I will be racing her in the open dinghy class at my club, as my experience grows (hopefully with making sails and racing her) then it will be great fun making a radial lug, a cool sail indeed.

The discussion about hand sewing / machine sewing for a vertical panel sail is very timely. Can I offer an in-between stage. My son has just bought an industrial Singer sewing machine, off of eBay, which is made for sewing leather. Pretty tough then. It features a moving foot where the needle and foot all move together to help pull the cloth through. It does not zig-zag. So the seams will have to be straight. Finally, to be as close to hand sewn as possible - it has no motor, it is turned by hand!

If I should not use this machine, then I will try and repair my broken one which will sew sailcloth, it stripped the gears on a very thick cover. I have new gears but cannot fathom how to fit them.

The heavy duty Singer is quite a vintage looking machine but they are still made. Will try and locate a picture of it.

[norseman]

I agree Todd, when you talk I listen. However, this thread started out with the possibility of using polytarp for sails. And we're in total agreement there as you discuss in your book. A waste of time and money.
So, considering a good machine will cost at least 1000 USD (up here at least) even used, spend the money on proper sailcloth instead. Say performance cruise 4.18 oz, or similar as it can be hand-sewn. Have fun.

Cheers

[kenjamin]

My wife and I sewed the sails for my Caledonia Yawl on her Bernina Sport (an old base model) but it did have a walking foot and did zig-zag. Her machine probably is worth about $250 US. The sails turned out fine as the panels were computer designed by Jeff Frank at Sailrite and with Mr. Grant's books (again Sailrite) giving us many helpful techniques, we got the job done without a lot of problems. We went through a few needles and undid several bird's nests of thread but all in all it was a very satisfying experience. Lubricating the thread is of upmost importance when using a home machine designed really for dress making. We used a silicon spray to saturate cotton balls and then the thread was run through that to keep everything running smoothly.

[keyhavenpotterer]

Well, I bit the bullet yesterday, purchased a roll end of 4.2 oz white Dacron to have a go at this sail making. Enough on the roll to have two attempts at both main and mizzen. Please don't post that 4.2oz is the wrong weight - too late now. The Sailmakers Apprentice says 3.9oz is good for a dinghy sail so looked for 4 oz to 5oz which my Scow sail is made from.

Back to the book now. How to cut it, which thread, what size grommets. Anybody know where I buy a hot knife? All help welcome.

Settled on a 4 panel vertical cut and a two panel vertical cut mizzen.

http://strathkanchris.files.wordpress.com/2008/12/raid41-700-vertpan.jpg?w=499&h=707

Brian

[ChrisBen]

Back to the book now. How to cut it, which thread, what size grommets. Anybody know where I buy a hot knife? All help welcome.
BrianSailrite has everything you need. This hot knife works well but a little pricey at $130 for your one time use. Engel Hotknife Without Blade 110 Volt (http://www.sailrite.com/Engel-Hotknife;jsessionid=0a0109441f439985eea4e8ef4522a4 bbe203a1d9cc73.e3eTaxmKbNaNe34Pa38Ta38NbNr0?sc=1&category=-101)
This type of soldering iron is all you need and can be found in just about any hardware store. Just make sure you get the flat blade for it. Weller Soldering Iron (http://www.sailrite.com/Weller-Soldering-Iron-Hotknife) Slip a metal yard stick or piece of sheet metal under the cloth and use a metal straight edge as a guide along your pencil line. You want to use the dabond polyester thread with uv protection also available from sailrite. Polyester Thread - Canvas Thread & Sailmaking Thread (http://www.sailrite.com/Categories/Polyester-Thread)
Use spur grommets, #0 or #1 for lacing maybe #2 for the corners if needed. Spur Grommets for heavy applications (http://www.sailrite.com/Categories/Spur-Grommets)

[keyhavenpotterer]

Thanks ChrisBen. I have a soldering iron, so that's a great tip. (forgive the pun). Thanks for advice on thread and grommets too.

Brian

[kenjamin]

When I bought my hot knife from Sailrite, they had a cheap one for about thirty dollars (US) that I never did use for cutting sail cloth (all pieces were pre-cut in the kit I bought from them) but it sure came in handy for finishing off the ends of all the cords that hold my battens in.

[Todd Bradshaw]

4.2 oz. is fine. Anything between 3.7 ounces and 4.3 or so is considered "four-ounce". For just a couple of sails, I probably wouldn't even buy a hot-knife. I own three of them, but actually use them very little on sails made from 4-5 oz. Dacron. The fancy Engel is great for cutting heavy stuff (rope, Sunbrella, etc.) but awfully aggressive on 4 oz. Dacron. The standard Sailrite (modified soldering iron) works well and I've had mine since 1980 when I first started working on balloons, but it's hard to get a really neat even cut on a long edge. I've also got a smaller one that cuts spinnaker fabric and that's about it.

On four ounce cloth, they all tend to leave a pretty nasty black bead in places if there is any variation in your feeding speed. It's not pretty on the Tanbark cloth I use and is downright ugly on the Egyptian-colored Dacron - as well as being a fairly irregular-looking cut. The computer cut sails from Sailrite are cut out by a spinning cutting wheel while the cloth is sucked down tight to a big vacuum table. The wheel is not really intended to melt the edges in the process, but it does to some extent and it helps seal them.

Over the years, I've tried nearly everything, including rolling the fabric very neatly and tightly on the cardboard tube and cutting the whole works, tube and all, into chunks with the band saw. Needless to say, the first time I stuck a $200 roll of fabric in the band saw, things were a bit tense. It worked and did create a bit of edge-sealing friction, but the results tended to be too unpredictable. Any slight variation produced a series of shallow, repeating waves down the edges of cut pieces which were supposed to be perfectly straight.

These days, I use a 6' metal ruler and a utility knife to split panels and cut luff tapes and other parts. You get a few stray threads raveling out over time, but the stitching and seam tape prevent any kind of structural problems or anything more than a strand or two coming loose. I tell my customers that I'd rather take a few minutes with a pair of sissors once in a while to trim any loose threads than to have ugly, black, melted panel edges showing all the time.

V-46 or V-69 thread is fine, #0 spur grommets for edge lacing or the little reef patches, #2 for corners and the ends of reef lines. I usually use 1/2" Venture Tape of 3M Super Seam-Stick for basting.

[keyhavenpotterer]

Have been looking for a UK supplier for the 3M Super Seam Stick, thinking that 3M products are generally available here. Not found it yet but have located the more standard acrylic tapes. While looking I came across this interesting post on the Cruising World site about just how strong the 3M 5200 glue is - seems it is stronger than stitching when used to glue two pieces of sailcloth together.

http://www.cruisingworld.com/how-to/projects/magic-goo-to-the-rescue-201615.html

I was aware that mylar sails can be glued but up to now had not found a glue that could do the job for Dacron. The article mentions just how hard controlling the glue can be and using the cheaper double sided tapes can help control the two pieces of cloth whilst glueing a repair.

So, just pondering if it might be possible to use a narrow tape say 1/4" to hold the panels together, then run a bead of glue in the overlap if that were say 3/4" between the two panels.

Anybody tried it? Since most boat builders are ok with epoxy glueing, might more make their own sails if they were glued?

Brian

[James McMullen]

The advantage of putting your seams together with thread instead of glue is that it is much easier to go back and remove the thread to start over if you did something wrong or irregular or in the wrong order.

[Todd Bradshaw]

Dimension Polyant Sailcloth has been selling an air-powered hot glue gun to use in conjunction with a basting line of 1/4" tape, instead of stitching, for quite some time. You baste one side of the seam with the seam tape, stick the nozzle of the gun under the flap, shoot a bead of glue in there and roll it down. Drawbacks are the cost of the gun ($2K) and that you need to do a lot of seams at once, because once opened, the glue cartridges have a fairly limited "pot life". If you could control the excess and had space for it to dry flat, 5200 might do the same job just about as well..."Honey, do you mind if I spread this sail out on the living room carpet for a little while?"......

[keyhavenpotterer]

Managed to clear enough room in the lounge. My Raid41 mainsail has a 16' leach, look very long laid out there in front of me. cannot use spikes though! Need to use more tape to hold the cloth steady though.

Only managed 15 minutes before my back went again so had to stop. Did realise however that those seams are pretty long and perhaps I should use my cloth at it's 1500mm width rather than splitting it.

This would reduce the sail from a 4 panel to a two panel sail. Thus only 1 seam to sew/glue. I tried the layout in Sailcut4 and it looks ok but would it set ok in real life? The Raid41 concept is after all about low cost simple fun, so a simple sail suits the boat. Or is it too much simplification?

Here is a drawing of the sail and the shapes if I can load it.

[Todd Bradshaw]

Is it possible to build the sail with only one shaping seam? Probably, though its effectiveness may vary greatly depending on the firmness and bias stability of the cloth chosen. Softer, less stable fabric will tend to smooth out the shape a lot more than most Dacron will, avoiding generating a ridge along your seam.

The cut, however, is most curious and in my opinion, you have passed the point where the computer is helping you and it is actually hindering the project. The plan on the left is what the Sailcut program is suggesting.

http://webpages.charter.net/tbradshaw/X1.jpg

The shape that this cut is going to generate is dead flat for the bottom 2/3 of the sail. Maximum draft (and most of the generated shape) is about where I have placed the red dot. That's not where we usually put either max draft or most of the shape on a sail of any type. We would normally put it down near the position of the blue dot. A certain amount of slack in the outhaul tension will generate a curved chord shape in the lower part of the sail, but it's pretty rare to try to produce all your lower shape by outhaul tension alone and not have much of it designed and built into the cloth. In addition, the foot and foot-round area is also dead flat. A round without shape is called a "flap", because that's what it usually does.

In order to generate something that's actually shaped like a sail, the computer would need to be producing something more similar to the plan at right. It's shown as a traditional broadseam, where the cloth panels' edges would be straight, rather than cut in curves like the left plan. The red area is how you would overlap the two panels at the seam to make the sailshape, and as shown, your seam overlap would vary along its length to generate that shape (it's exaggerated a bit since we're working with a small drawing here). Maximum draft is about 40%-45% above the bottom, where the seam is narrowest. Below that spot the gradual broadening of the panel-to-panel overlap creates a slightly cupped shape in the lower third of the sail with a slight flare in overlap at the very bottom to cup and stabilize the foot roach (I'm freehand drawing in Photoshop here, which ain't easy compared to my drawing programs, so in reality the curves would be smoother).

The same sort of panel overlap increase (broadseaming) would also be happening above our maximum draft spot, as we head toward the top of the sail. We want to gradually build a slight cup-shape into the top third or so with a little flare right along the head edge. In this case, we use somewhat less broadseam because our chord width is smaller, and less flare because the head area doesn't need, and will not tolerate, too much shape up there.

On a computer cut, they use constant-width seams and cut the panels with curved edges, rather than the constant width panels and broadened seams of traditional construction. They would essentially cut out the red area, leaving the panels with curved edges and then join those two curves with a constant 5/8" seam overlap to generate the same sailshape. The plan at left does that from its top down to the red dot, but there is no shaping at all below the red dot. Two thirds of the sail (including most of the sail area) is just a flat panel, cut to a perimeter shape that looks like a sail.

The nice thing about computer designs is that the computer can quickly and very accurately see the 3-D shape of the sail and figure out how to generate it with a bunch of flat panels. In this case though (maybe because the design is too over-simplified by only having one shaping seam) the end result is not going to make a very good sail. If you want to see for yourself in three dimensions, plot and cut out the pieces of both plans on typewriter paper about 12" tall and tape the seams together. Then lay them flat on a table. The left plan will make a sail that has a hump near the red dot and which is dead flat everywhere else. The plan on the right will make a shape that looks a lot more like a real sail.

[keyhavenpotterer]

Hi Todd, looking at page two of the xy plot on the sail development pdf in my post above:

the Sailcut4 programme cuts one seam edge straight, in this case the larger main leach panel and puts the shape into the next adjoining seam panel. Not broadseaming and not normal cad I guess?

thus the smaller luff panel y plot along the seam edge gives, from the bottom to top of the panel:

+33.7 -10.5 -26.3 -29.1 +33.7

So there is over 62.8mm "shape" overall on the seam, with much more shape change in the top section. Is that some shape as you would have or basically flat?

Thanks again, Brian

Sounds like a two panel Dacron sail is a risky venture though?

[Todd Bradshaw]

It would appear to add more shape that I originally thought it would just from looking at the panel shapes on the pdf, but it's still in the wrong places. You don't put your maximum shaping up near the head on a 4-sided sail. In fact, If you took all those measurements and reversed them, top to bottom, it would provide a more normal sailshape. You want your deeper, more dramatic curve in the lower part of the sail where the chord is bigger and the draft is deeper and you need to shape the foot round to prevent flapping, not up high.

Some software systems mate a curved edge to a straight one, others will split the difference and curve both edges. On Dacron, it doesn't usually matter, although it's sometimes easier to baste similarly-shaped edges together prior to sewing, than to have to force all the curve into one edge as you stick panels together. The exception is spinnaker fabric, or other light or fairly unstable fabric. In that case mating similarly-curved edges will tend to provide a much smoother shape. because it tends to align the yarns (and whatever stability or stretch resistance they contribute) similarly on either side of the seam. Here is an extreme example of that principle, done in nylon. There are twelve vertical gores making up the shape and each gore is divided into sixteen small panels stacked vertically. The top or bottom edge of every panel is a mate to the edge it joins on the panel above or below it. These curved edges gradually change from shallow curves near the top, to deeper fuller curves at maximum girth and back again to shallower curves near the bottom. In addition, the long vertical seams joining the gores are also the same shape. This uniformity of thread line orientation across the seams makes the finished shape smoother, especially when pressurized, and also makes the overall shape better able to absorb and survive outside forces that might distort it. Mixing straight and curved edges on seams for something like this would be a good way to end up a pancake.

http://webpages.charter.net/tbradshaw/balloon%20001.jpg

...what? You mean everybody doesn't have a balloon in their living room? There is certainly something to be said for spreading the required amount of curvature over several seams though, especially on a boat, with fabric as stiff and stable as Dacron. It may make the seaming job more work, but it's usually going to make a smoother shape.

[keyhavenpotterer]

I have been back to the design and looked at it from lots of angles by revolving the image. Looks pretty bad from below. I have taken a screen dump and will post as a pdf here. ( pdf too big)

Even the software shows it as a poor shape! Not the way to go!

Loosing heart a bit. A flat cut bendy spar polytarp solution is available for Raid41, I just thought a low cost route to a Dacron sail would be good too. Sailrite is available for the USA I guess. I am certainly enjoying the learning process.

Going up to help assemble my boat, it's in flat pack form at the moment, in mid Feb. Will be able to measure the spars for bend then, as per your book, Canoe Rig. Will be good to have those measurements and then try to sort something out. Hopefully my back will be better by then as well.

Brian

[keyhavenpotterer]

been trying to think through aerodynamic shaping for a vertical panel lug sail.

Imagine making a scale model sail. here is the daggerboard shape of my new Raid41.

http://www.woodworkforums.ubeaut.com.au/attachment.php?attachmentid=91037&d=1228847646

There are about 15 to 16 laminations in the foil. So lets say, 16 and I aim to make a four panel vertical sail. To keep it simpler for my weak brain, lets eliminate twist. Also to help, lets have a loose foot and a loose head! Bit like me. Also lets have a constant camber all the way up the sail, ie the same as the dagger board.

So I can cut 4 straight edged parallel sided panels and lay them vertically onto the curved surface. Glue the seams. Can then cut the angle for the yard and the angle for the leach.

Now I have a lovely aerodynamic sail. Loose foot and loose head.

If I had to bring the foot into a straight edge to fit the boom, lots of shaping would be needed, as per my current Scow lug sail.

http://farm4.static.flickr.com/3200/2790553290_1d0ebbd921.jpg?v=0

The question is how would this loose foot and loose head sail "keep it's shape" in real sailing conditions. It's aerodynamic but seems to have nothing to hold the shape "in shape" at all?

Would good full length shaped battens do it? is that why most sailing canoe have them.

If I now remove the strange concept of a loose head, the cloth will need broad seaming to fit the spar. Now this would give me some control over keeping the shape of the sail the way I want it. Probably might help the top section of the sail, what about the bottom half?

However, I want to have a loose foot sail. So, is this why we need broad seaming in the foot? Or could I just use full length battens to hold the shape?

Anyone who is following this please award yourself a biscuit!

Brian

[Todd Bradshaw]

Q:"The question is how would this loose foot and loose head sail "keep it's shape" in real sailing conditions. It's aerodynamic but seems to have nothing to hold the shape "in shape" at all?"

A: It won't. Abandon the idea of a loose head immediately. It's a can of worms that you do not want to open. A loose head will sag. As it does, the draft in the top half of your sail will increase and you won't have any control over it. As the wind picks up or you sheet-in harder, it will sag more, complicated by the fact that the yard will bend more (moving the throat and peak corners of the sail closer together) and creating even more sag along the sail's head, and subsequently more draft in the sail. This is the opposite of what you want to be happening at these times. In higher winds, or in situations where you are sheeting in hard, you want the top of the sail to get flatter, not more drafty. There is, however, a limit to how much you want it to flatten due to yard bend, which is why a certain amount of extra round should be added to the head to compensate for yard bend in use.

Full battens are not going to fix this and will simply add another layer of unpredictability to the project. Most sailing canoes that use full battens use them either to support a big roach or to make slab reefing easier (as a means of neatly pulling down a big hunk of cloth across the entire width of the sail, using the batten as a "handle"). This was developed back in the days of soft cotton sails. Dacron fabric, being much stiffer, doesn't scrunch down as easily or as neatly, so roach support is their main function these days. On a typical, modern, non-roached small-boat lugsail, full battens are of little or no help and often do more to mess up the designed and sewn-in sailshape (by overly flattening it, in terms of overall draft, draft placement and entry angle)) than to help it. They also create a lot of extra work to build-in and are a major source of chafe.

Q:"However, I want to have a loose foot sail. So, is this why we need broad seaming in the foot? Or could I just use full length battens to hold the shape?"

A: Broadseaming in the foot area on a loose footed sail is used to position the maximum draft at the proper spot on the lower part of the sail, to slightly cup the foot area so that it doesn't flap, and to allow you to build a bit of round into the foot so that it doesn't look chopped-off and crude. Again, full battens in this case will likely do little more than complicate the issue and mess up the shape you're trying to build.

[keyhavenpotterer]

Thanks Todd. Promise, I was only thinking of a loose head as conceptual idea.

Since the fixing to the gaff yard assists the holding of sail shape and to some extent the boom as well, vertical panels with seams going into these spars makes sense for a balanced lug sail.

Following on from this idea of a flat sail laying on an aerodynamic foil, edge curving can also help hold the shape. This would indicate securing the foot to the boom might make keeping sail shape easier?


Brian

[Todd Bradshaw]

Brian, whether it's built with traditional broadseams or with computer-shaped panels, there is really only one form that a vertically-cut, four-panel, loose-footed lug can take. The difference between traditionally designed and computer designed in this case just boils down to how the three panel seams are handled. The rest is exactly the same. There can certainly be dimensional variations in various aspects from one sail to the next, but the basic plan is the same.
Here is a nice lug plan that I borrowed from Gavin's Oughtred Elf, which makes a very nice looking sail with a pleasing profile.
http://webpages.charter.net/tbradshaw/!LUGPLAN1.jpg

Details:
- The leech is slightly hollowed to prevent flapping (around 1" hollow per 6' of leech length)
- The luff can be either cut dead-straight or slightly hollowed. Lugsail luffs are under a lot of tension, so they need to be well reinforced. Larger sails can benefit from being hollowed as it helps to prevent luff sag (and the extra draft it can create). In use. the hollowed luff is pulled straight by luff tension. Smallish sails often work better with a straight luff. There often simply isn't enough tension generated along that edge to pull a short, hollowed luff straight, so the hollow isn't contributing anything. A well reinforced, straight luff is usually a better option on these small lugsails.
- Foot round is done mostly by eye to get a nice looking profile shape. Maximum round is about 45% of the foot length aft of the tack and the aft third or so of this foot curve is pretty straight (prevents flapping back there).
- Head round is fairly modest and of the amount or round added, about 1/3 is for creating draft and about 2/3 to compensate for yard bend in use.
- corner patch design, reef lines and other details are up to the builder.

This drawing shows the areas which will be shaped - either by broadseaming (traditional construction) or by cutting curves into the panel edges, guided by the computer's calculations. All the shaping in this sail (other than the rounds and hollows listed above, which are actually just profile modifications) will be done inside these two blue zones. The entire rest of the sail outside of these blue areas is dead flat. The deepest draft in our sail will start and stop at the peaks of those blue triangles, near the middle of the sail, and run vertically along a line connecting them. As you can see, there are five spots where panel seams will cross the triangles, so these will be the places where we can develop our 3-D shape.

http://webpages.charter.net/tbradshaw/!LUGPLAN2.jpg

If we strip away the trim - corner patches, grommets, edge finishing, etc., our four panels would look like this, with the shaping areas noted by the red dashed lines.
http://webpages.charter.net/tbradshaw/!LUGPLAN3.jpg

This is where the two construction methods differ, and I'll give you the quickie, nutshell versions of both. All shaping of either method will be inside the blue areas.
In traditional, broadseamed construction, we use straight-sided, constant-width panels of cloth. The seams between the blue areas are straight and a consistent width, normally about a 1/2"-5/8" overlap from panel to panel. Once we come to the red line on our lofting and enter the blue triangles on either end, we start to broadseam from that point out to the edge (head or foot). All broadseaming means is gradually increasing the panel-to-panel overlap as we approach the edge. For most cruising Dacron, we increase the overlap by about 1/2" for every 30" or so of broadseam length as we baste the two panels together. So, a 1/2" wide seam that was 30" long from the red line to the edge, would end up being about 1" wide by the time it reached the edge. The widening is done in a smooth, gradual curve for most of it's length, but for the last 10%-15% or so, the overlap rate is increased slightly, giving the broadseam curve a little bit of flare at its end. This helps firm up the edge, especially along the foot curve to prevent foot flapping. A short broadseam, like the one near the throat corner, might only be 6" long, so the overall seam width increase would be very small. Unusually soft or unusually firm (stiff, extra stable) fabric would be broadseamed in the same spots, but the overlap increases would be different. Softer cloth can use less overlap increase because it tends to stretch more (maybe 1/2" for every 36" of broadseam length). Stiffer, firmer cloth needs more overlap increase, due to it's lack of stretch and increased stability (maybe 1/2" increase for every 24" of broadseam).

If you happened to be making the sail from eight panels, instead of four, you could either broadseam only some of the seams in the blue area or broadseam them all , but reduce the overlap increases to get the same final shape. Traditional sailmaking is learned over a period of time as you get experience and develop a feel for designing and assembling sails - how much to broadseam and where to do it.

The primary function of computer design programs is to see the 3-D shape of the sail in their little micro-brains, determine how to duplicate it with pre-cut flat panels and eliminate the years spent learning how to broadseam by eye. If given the right tools and proper input information, they do it extremely well. For this four panel lugsail, the computer will output panel shapes that look like this (not drawn to scale and curves are exaggerated a bit to show up on a small drawing):
http://webpages.charter.net/tbradshaw/!LUGPLAN4.jpg

The broadseam areas have been dealt with by cutting curved edges on the panels in the same places. These panels can now be basted and sewn together with a constant-width seam overlaps, everywhere on the sail from top to bottom. This makes the assembler/sewer's job easier - to the point that if they can sew a consistent 1/2" seam, that's all they need to know. The computer already did all the shaping. On either side of the red arrows above, the computer has cut the proper curves, complete with the little flare at the edges, so that no seam width adjustment is needed. The 3-D shape of the two lugsails will be exactly the same, assuming that the data for spar bend, desired draft, etc. which were entered into the computer and the sailmaker' brain were the same. If your computer plan is not outputting something that looks very much like the last drawing, then there is something seriously wrong happening.

[Eric D]

Todd,

let me say this...coming from a power boater mind you....

I am in total awe of what you have put into this thread. This is your livelyhood and if I came to your shop you would be making money on the very advice you give here for free. You sir are an assest to mankind and this forum.

Just shows the world how nice guys from WI can be. Have a great day.

Maybe someday threads like this will convince me to give up the old stink pot for a sail in a BBSB to my favorite hunting grounds.

Have a great day all, sorry for the quick drift....now back to the best on line sail tutorials.

[keyhavenpotterer]

Todd, I just do not know how to thank you for your tremendous help. It will take me a while to go over all the details, I just had to respond as Eric D has with a really heartfelt thanks. Nice that you used an Elf sail as an example. I was lucky to sail in one last autumn as thought she was lovely.

Looking at my output panels some are reasonably close to your broad seaming, some are not. There is one control that I have not really looked at yet in Sailcut4. That is "Mould" shape. This changes the aero profile of the sail and in particular the leading edge. I have set the three sections, top, middle and bottom to different settings.

The top section I have set to max "luff setting" = 18
The middle to 11
the bottom to 3. all my settings were three before. A flat entry.

The 11 settings gives a shape much more like my Raid41 dagger board shape.

I will play with these settings to see if I can produce panels which meet normal expectations! Have change the aero profiles and now the broadseaming is much more in line with expectations.

The pdf is too large again.

think I might be getting there - there being the tiniest understanding of sail shaping.

Brian

[Todd Bradshaw]

Thanks, guys. I found a typo on the broadseam lengths for soft and firm cloth and fixed it. It will make more sense now. Coming from the cornfields of central Illinois and a family that didn't sail, I learned this stuff by reading what books I could find and by asking a lot of questions (many of them most likely dumb ones at first) of people who were willing to share their knowledge of sailmaking - Jim Grant at Sailrite, in particular, was a wealth of patiently delivered free information. It's only fair to pass it along to others interested in building sails. Just remember that after about 25 years of it, your knees will really hurt from crawling around on the floor!

[keyhavenpotterer]

Here is a link to a pdf file which shows the "Sail Mould" screen entry on Sailcut4. I have been unable to post the pdf since it is too large.

http://strathkanchris.files.wordpress.com/2008/12/raid41-sail-shape-26-01-091.pdf

Their are three sections to the sail shape. Top, middle and bottom.

Each section has three inputs to control shape. Leading edge, depth and leach shape. It also shows how far back maximum draft is.

The input figures I have been using are shown in the bottom sail shape. Luff set at no 3. The result is a fine entry and leach but a bunching of the draft, and hence my sail panels had shape in the middle seam but not much in the two other seams.

The middle section shows a much nicer shape, luff set at no 11, much more like the profile Michael Storer uses for his foils. The really nice think is that with these settings the panel shapes are much more like the panels expected from normal broad seaming. So fine tuning these numbers seems to be the answer.

The upper section shows an even stronger curved entry, flatter mid section. Changes to the leach setting make a big difference. Not sure which will be best yet.

Brian

[Todd Bradshaw]

Did the computer happen to mention how it plans to generate that nice rounded entry angle with only two pieces of flat fabric, joined by a single seam that isn't in a particularly good position or orientation for broadseaming/shaping? That should be a pretty interesting trick.......

[keyhavenpotterer]

Mmmmmm.... not sure about that. Glad you like the shape though.

At least the "broad seaming" looks a little more similar to your panel broad seaming with these setting.


Here are the panel shapes outputs - oh dear, fingers crossed!

I am thinking that I might be able to use the software to help me with overall panel sizing and shapes and broad seaming allowance, since I cannot spike the cloth to my lounge floor! Then broad seam as per your illustrations. Combine the two, kind of thing.

Brian

[Todd Bradshaw]

Yes, from what I can tell from the PDF, the panel shapes are looking a lot better. They will not generate entry curves which are as round as those shown on the previous PDF (they will all tend to be flatter, more like the bottom one) but that's pretty typical of vertically-cut lugsails. There isn't really a good way to change that or do a lot of entry-shaping on a lug's luff without switching to a cross-cut or very narrow vertically-paneled cut, where you have a whole bunch of panel seams hitting the luff to play with.

This is partially due to the fact that this type of sail was originally developed for natural-fiber cloth, which is much more stretchy. A cotton sail would usually have more depth/draft/round along the luff, just because of its stretch and limited stability. Modern Dacron is more of a "what you build, shape-wise, is what you get" situation.

These days, when we build a vertically-cut lugsail from modern Dacron, we are essentially building an "historic replica" of sorts. We do it because that cut looks the way lugsails are usually supposed to look. If performance and subtle shape adjustment in the design were our main criteria, and we were willing to build enough copies to experiment and adjust our adjustments until we got the best performance, then a cross-cut would make more sense. If you get my drift...

[keyhavenpotterer]

Thanks Todd for your view of my latest try.

I was concerned at my first attempt at physically laying out the panels that a 16' leach panel makes it very difficult to layout in a normal living room, with room needed around it to work on.

So, for Raid41 builders who may like to also make their own sail, a layout with shorter maximum panel length would be helpful. Using a cross cut layout does shorten the longest panel length to just under 9', which would help a lot when working in the lounge. If it helps produce a more stable shape then that's good too. I am after all a very keen lug sail racer and there are a lot of very well sailed lug rigged dinghies around here, i.e. Lymington and Keyhaven.

Here is a pdf of exactly the same sail, every setting the same except the panel layout changed from vertical to crosscut. My first look at the panels indicates that panel 4, the one which comes into the yard/vertical luff intersection has the most shaping, the lower panels surprising little?

Interesting, when trying to help newer lug rig sailors tune their rigs, I tend to concentrate on explaining the need to have the sail luffing first at that intersection point. Not higher up the yard. And to bring it to the right place by easing the yard outhaul, so that when full downhaul is applied (6:1) in our case, the sail luffs cleanly at that corner of vertical luff and yard. (We shackle the sail at that corner point, the front of the yard to stop all the downhaul tension going straight up the yard.)

Do these panel shapes make sense at all?
Thanks again,

Brian

[Todd Bradshaw]

It's hard to tell much by looking at the pdf and reading the coordinates while trying to make a mental picture of what the panel actually looks like. I could be wrong, but I do get the feeling that this program has some strange desire to put maximum shape into the top of the sails it designs and leave the bottoms almost flat - which isn't the way sails are usually shaped. Draft and shape inducing features (broadseaming, panel-shaping, etc.) are almost always used in proportion to the chord width of the portion of the sail where they are located (wider portions of the sail get more shape than narrower parts). On four-sided sails of any sort, the throat area is pretty touchy about shape. If you build in too much shape there, the area doesn't set properly and that can cause problems (wrinkles, creases, distortions, etc.) that may affect the entire sail. For this reason, throat areas are usually cut pretty flat and shape added along the luff is usually pretty much tapered out to nothing as you get near the throat.

Again, whether you're broadseaming on the lofting floor or designing using a computer and shaped panels, the basic shape generated should be the same and the construction differences between the two methods are pretty minimal - basically just how the seams between panels are handled.

Here is a plan for a cross-cut lug. I used five panels to give me one more shaping opportunity along the luff. I'll just post the url since this thread is getting really slow to load due to all the graphics.

http://webpages.charter.net/tbradshaw/CROS-LUG1.jpg

Aside from a bit of round along the head and foot, all the shaping in this sail would be done at the sections of the panel seams marked with the dashed red lines. The rest of the sail is dead flat, and would be with either traditional broadseamed or computer-designed-panel-shaping construction. The blue curve is the broadseam curve. It shows where the luff broadseams would begin and they would extend forward, all the way to the luff edge. The computer plan might not show this curve, but it's thinking about it somewhere down inside its little mechanical brain. Broadseams would be made using one of the typical "length-vs.-overlap-increase" formulas, tempered for the stability of the cloth being used and with a slight flare (increase in overlap rate) as the seam gets close to the edge.

The flare, and how much we increase our panel seam overlap ratio at the luff end of the broadseam is what determines our entry shape and angle. More flair makes for a more rounded, fuller entry. Less flare makes for a flatter, less rounded entry.

There are also a couple of leech broadseams shown. These are just slight increases in panel-to-panel overlap at the leech. Typically, they will start about 18"-24" from the leech and their total increase in overlap when you have reached the leech edge is seldom more than 1/8" or so. Their function is to help keep the leech tight and flap-free as the sail ages. These broadseams have no flare at their ends. We don't want to "hook" the leech, we just want to gently firm it up a little bit.

If we convert this traditional plan to a computer cut, we will simply be replacing the variable-width seam overlaps on straight-sided panels, with constant-width seams joining panels which have had their edges pre-cut to specific curves. If we do it like your program, all the shape will be cut into the bottom edge of the upper panel at each seam. The upper edge of the lower panel, which joins it, will be left straight. The panels should look something like this (not drawn to scale and curves exaggerated a bit to show up better).

http://webpages.charter.net/tbradshaw/CROS-LUG2.jpg

Aside from a few small differences in the amounts of this or that you choose, this is just about the only way you can cut a 5-panel. cross-cut lugsail. Whether it's traditionally broadseamed or computer panel-shaped, the difference is just the seams and whether you cut off the excess fabric at the overlaps (computer-cut) or leave it in as part of the seam (broadseamed). Notice how the curve cut into the luff ends flares at it's end as the rate of curvature increases. This is entry angle adjustment, just as it was on the broadseamed version. I just drew-in the two little leech tapers with red dashed lines because they wouldn't show up on a small drawing. In reality, the panel would be cut away just a tiny bit there.

All other seamed areas on the sail are un-shaped, straight seams. I'm not sure how close the computer plot is to something having this sort of panel shapes, but if it's going to work, the panel shapes had better be very similar.

[keyhavenpotterer]

It's been a while since we discussed sail design and sail making in this thread, but by way of a thank you to Todd who explained so much for us, here is a picture of my sails for RAID41.

I have to say that learning as much as I did and then trying to put it into practice gives me a huge increase in my already high respect for just how hard sailmakers have to work to earn their dollar and give us all so much fun.

After my back went into spasm with my very first attempt at laying out the panels, I was suffering from sciatica without realising it, I had to have a three month break even before I had started! Michael Storer gave me good advice to first build a simple edge rounded sail to minimise time spent on my knees on the "loft" floor.

So the sails are a polytarp edge rounded design made from 4oz Dacron which MIK supplies as part of the boat design package. It was much harder than I expected to make and sew, so I think it was as well for this first attempt that we did not try broad seaming as well.

Most of the corners have 5 layers, some 4.

I think, although my back was very sore as I began laying out the sails, it held up well and now is stronger for the effort put in by a terrific chiropracter.

So thanks Todd, and here's to the next one!

http://farm4.static.flickr.com/3381/3518547661_c7c2ba90b2.jpg?v=0

Brian