Sail design

[Saint]

I've read this on sail making...
http://marina.fortunecity.com/breakw...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.



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]

Originally Posted by Todd Bradshaw

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/...-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]

Originally Posted by Todd Bradshaw

>>>>>>>>>>>>>
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.


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/sailmaki...mets/index.htm
http://www.duckworksbbs.com/sailmaki...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.



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.

[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.

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.

[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.

[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'

[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