Balanced Lug Rig Set-up

[Milli]

Even though there is still snow on the ground I am thinking of sailing and some possible modifications to my sail rig. My sail in a 70 sq. ft. balanced lug sail set on an unstayed mast. I have noticed that my boom bends when I set the tack line. I think this might be bad as it would pull the shape out of the lower part of the sail. The foot is tied to the boom, so I tried it loose-footed. I didn't notice much difference in how the sail set and am now wondering if I have the foot of the sail stretched too tightly on the boom ?

Any suggestions on what (if any) changes I should consider. As I see it I could try the sail loose-footed again and relax the tension in the foot of the sail. Alternatively, maybe I should get a new boom that won't flex as much (say a rectangular section) and tie the foot of the sail again. Could I be putting too much tension on the tack line (downhaul)???

Lastly, maybe I do nothing, re-tie the sail to my "flexing" boom and go sailing ???

My mast also flexes and I not sure how much of a concern that is as well...

[john welsford]

Go sailing, if it doesnt work very well then, and only then try and fix it.
A few hints, sails set best with a slight amount of twist, in this case the yard should twist away from the boats centreline a little more than the boom. To adjust that, move the halyard attachement aft on the yard for less twist, forward for more. To reduce twist when sailing off the wind, move teh boom forward relative to the mast, and to increase twist when running, move the boom aft.These simple rigs are very tunable ,and are quite sensitive to adjustment.
In my experience a little flex in the boom is not a bad thing.
John W

[Todd Bradshaw]

As John said, the first thing to do it try it out as designed and see if it works that way. Usually sailmakers will build-in an allowance for bend on both the head and foot of dinghy lugsails since light spars are bound to bend some. The amount of curve that has been added to these edges to actually create draft is on the order of an inch or two, as it doesn't take much. It's not uncommon to wind-up adding another two to four inches of foot curve for bend. When the boom bends and uses up this allowance, you're back to the original inch or two of round to create the proper draft.

The foot is usually cut and shaped differently for a loose-footed sail than it is for a laced-on sail and what works one way, usually doesn't work very well the other way. I would be inclined to stick with the laces and tweak things from that point, rather than loose-foot the sail.

You will also have the mainsheet system putting bending force on the boom. Sometimes it's possible to fiddle with the mainsheet attachment point or boom block(s) locations to get a more even overall, downward pull on the boom and reduce the localized bending at the tack line area.

I wouldn't worry too much at this point about mast bending. The Chinese used huge unstayed masts that bent or leaned in use and acted as shock absorbers in a puff. You need just enough mast stiffness to keep the luff tight, and a balanced lug it is usually more tolerant of bending without losing luff tension than a standing lug would be.

The outhaul needs to be tight enough to pull out the wrinkles along the foot. Over-tensioning it tends to pull draft out of the bottom of the sail and gather it along the boom where it doesn't do much good. It also puts a lot of strain on the seams and fabric, which usually crosses the foot at an off-threadline angle and is prone to stretching. Unlesss you are conciously trying to flatten the sail for performance on a particular point of sail, there is little reason to run your outhaul tension any tighter than is needed to smooth-out the wrinkles.

[dadadata]

Everything being equal a lugsail yard, boom, and mast should not bend at all. Not at all. Any bend in the spars just contributes to a slack luff.

Stiffen your mast as the first order of business.

Yes, it is theoretically possible for a sailmaker to make you a sail that would compensate for the boom bend, but I doubt that you're in this situation: and very few sailmakers could do this.

A lugsail doesn't work well if the luff is not TIGHT. You want a 2:1 or 3: purchase on the tack line (or downhaul). Hoist the sail with the halyard, and then, to finish setting the sail, whale on the tackline. Very few people are strong enough to get good tension in the tackline by just pulling on a line and cleating it. Plus, if it sags in strong winds, you're not going to be strong enough to tauten it.

Signed -- COD, sailed many a small lugsail rigged boat.

[Todd Bradshaw]

Sorry Craig, but that's just plain wrong. It is damned near impossible to build small boat spars that don't bend in use and it is something that any sailmaker that's learned how to build small boat sails properly takes into consideration. It's been true for over 100 years and modern synthetic fabrics which have limited bias stretch have made it all the more important. If you're buying sails for a dinghy and your sailmaker doesn't take spar bend into consideration, find another sailmaker. If you're building them yourself and aren't building in an allowance for spar bend, go back to the books and finish the learning process.

[dadadata]

PS

Lace the foot to the boom. A loose foot = more bending.

[ishmael]

Todd,

If you can address what you know to the "gunter v solent lug" thread, here or on the misc. boat related thread, I would apprciate it very much.

Thanks,

Jack

[Todd Bradshaw]

Done - other thread

[dadadata]

==
Sorry Craig, but that's just plain wrong. It is damned near impossible to build small boat spars that don't bend in use and it is something that any sailmaker that's learned how to build small boat sails properly takes into consideration. It's been true for over 100 years and modern synthetic fabrics which have limited bias stretch have made it all the more important. If you're buying sails for a dinghy and your sailmaker doesn't take spar bend into consideration, find another sailmaker. If you're building them yourself and aren't building in an allowance for spar bend, go back to the books and finish the learning process.
==

We'll just have to disagree on this one. In one sense, sure, you always want to compensate for mast bend or boom bend. Then I'm reminded of Tom Firth Jones' account of the making of sails for El Toro dinghies.

But someone using a lugsail is not racing a class boat. And this guy already has a lugsail. He's not asking us how to tell his sailmaker to get a good lugsail. He admits his mast and spars bend. He doesn't say how much.

All other things being equal (Jim Michalak polytarp lug, or something jiggered up out of a big old jib or what have you ...) the key to having a lugsail work -- even if it is a flat cut sheet of blue poly as the simplest possible case -- is stiff spars so you can keep a taut luff.

For a lugsail, you need spars that are, for all intents and purposes, as bend-free as is practical. This means spars of larger cross section than might otherwise seem 'right' on a small sail. In my case, with a whopping 30 sq ft sail, I added 3/4 by 3/4 strips to the existing spars (which were identical, all of 6 ft long, and about 3/4 by 1-1/4), though the mast is still too bendy. Getting the (excessive) bend out of the boom and yard helped a lot.

I don't see how "taking bend into account" with a set of spars which are too light is going to help the sailor maintain a taut luff.

We can quibble about "how much bend is bend", but there I say make your small lugsail spars twice as heavy as you think you need and shave them down. Or be prepared to beef up your first attempt with glued on fish battens.

In my view worrying about taking bend into account before making sure that the spars are stiff, is putting the leech before the luff. So to speak.

[Todd Bradshaw]

I'm not going to waste much time arguing sailmaking with someone who isn't one, never has been one and probably never will be one - but the farther you go, the more you show your lack of knowledge on the subject.

It's true that in general (though not always) the less your spars bend, the better, but making spars twice as heavy as you originally thought they needed to be, rather than learning how to cut a sail in the first place is stupid. Putting the "leech before the luff" is building a small boat sail before measuring the spars for bend or at least taking it into account before you start cutting fabric. It's standard practice.

To go along with it, a good deal of the reason that some people have such serious luff sag problems on lugsails and have to run such high downhaul tensions is that their luffs are improperly reinforced and/or cut wrong in the first place. The same thing happens when they try to build a jib and aren't aware of how you compensate for headstay sag.

On small sails, the fabric's weight and stability is often much higher in proportion to sail size than it is on sails for bigger boats. It is thus much less forgiving of some of the shaping errors that you can get by with on larger sails and cutting and shaping can be quite tricky. I find that the small sails that I build now often present much more intricate shaping problems than the big Kevlar/Mylar radial multihull sails that I used to build. Fabric weight and stability is one big contributing factor. The other is spar bend.

I've pretty much held my tongue here over the years with regard to poly-tarp sails. This forum seems to support both those who seek to do work of the highest quality and those who for lack of a better term and with no insult intended, lean toward more quick-and-dirty boatbuilding with wood being the primary component. The two sides seem to get along admirably and there are those here who practice both diciplines.

Poly-tarp isn't all that different from the Mylar/polyester-scrim-based sail fabrics used for racing and beach cat sails. The real sail fabrics are more durable and more stable, but the principle is pretty similar. My biggest complaint with the poly-tarp and duct tape set has never been the material, it's the design and the cuting of their sails. Whether it's a whole website full of pics of Weekenders where the scrim in the "sailcloth" is all pointing the wrong direction or pictures of a boat that sailed down the east coast with a polytarp jib with a big bag right behind the luff wire, many of these sails demonstrate a profound lack of knowledge of how to cut a sail out of any material.

I spent about 20 minutes the other day on Michalak's website reading an essay on how to add darts to polytarp sails to improve their shape. It had formulas. It had drawings. It had pictures. After getting my mind thoroughly boggled by the intensity of it all, my reaction was "Sailmakers don't usually use darts because they aren't very strong and tend to make lumps in sails. This is more complex than learning how real sails are shaped. Why not just learn to do it right?"

I have no idea what Milli's sail is made from, who made it and whether they made it properly. In any case, the advice that I gave is based on 23 years of making small boat sails. Perhaps I'm wrong to assume that people want to know the correct way to build them in the first place. The best idea for this boat is still to do nothing and try the sail out on the water before changing anything.

[dadadata]

===
I'm not going to waste much time arguing sailmaking with someone who isn't one, never has been one and probably never will be one <snip>
===

Owww. I think we heard two different questions from this guy. In general I have found your many posts on the WB forum knowledgeable and interesting. But there is no "one way".

I wasn't arguing, and I have never represented myself as a "sailmaker" much less a capital-s Sailmaker, so your point is ... ?

I do understand how to rig and sail a small boat. I'd rather not be sniped at from the Heights for offering some simple and pertinent advice for someone who - according to the way I read the question - is trying to figure out the whys and wherefores of a particular sailing rig. John Leather is my "guru" for understanding lug rigs -- aside from using them on a half a dozen small boats and watching how things go -- but not everyone has read such hard-to-find stuff.

Fooling around with a boat and a rig may not be legitimate to you but it's legitimate for quite a lot of us, and it doesn't make us "wrong".

By the way, bendy masts are a no-no with Chinese lugsails. I don't know where this notion of bendy Chinese masts suddenly has come from.

Well, I'm going back to my igloo here in Maryland <chuckle>.

[Todd Bradshaw]

The problem is that some of your "simple and pertinent advice" is not great advice.

D.D. Quote: "Everything being equal a lugsail yard, boom, and mast should not bend at all. Not at all. Any bend in the spars just contributes to a slack luff."

This is not only quite unrealistic unless you happen to be in the carbon fiber business, but sheeting hard, using up the bend allowance and flattening the sail often improves windward performance. While sailing downwind under lighter sheet tensions you may also get a boost by having more draft in the sail. I'm trying to think of a rig and sail type which actually performs better (or would perform better) with absolutely no bend in the mast, boom and yard and can't think of one other than a solid wing and even they have panels that move to compensate for different conditions. The junk rig is close, but the unstayed junk masts did bend in use.

The "notion" of bendy masts on Chinese lugsails comes from sources like Jeremy Howard Williams book "Sails" - Fifth edition, Chapter 12 Chinese (Junk) Rig, page 363:
"The two most obvious aspects for the newcomer to the rig are the silence and the easy motion of the boat. She is silent because the full length battens stop the sail flogging, even when head to wind. She is easy because the unstayed mast, rather than the boat leans with the puffs, so that stresses are shed from the system."

or from Marino's "Sailmaker's Apprentice" - "Chinese Lug Rig" page 41:
"In it's original unstayed form, the rig permitted a bending of the mast like a tree in a breeze, thus spilling wind and providing a safety factor."

D.D. Quote: "Yes, it is theoretically possible for a sailmaker to make you a sail that would compensate for the boom bend, but I doubt that you're in this situation: and very few sailmakers could do this."

Quote from Jim Grant's book "The Mainsail Manual" pages 23 & 24:
"If the mast is flexible, however, one must determine the "normal" curve of the mast and add enough extra cloth to provide for this degree of flexibility."

Marino page 261 - Head Curve, Gaff Lug and Spritsails:
"The shape and extent of the head curve is very much affected by whether or not the head is bent to a yard or a gaff; and if so, how much the spar will bend"
page 262 - "The luff of a standing lugs'l may be cut slightly hollow to allow for sag. A smaller camber ratio is needed in the head of this sail to compensate for gaff sag."

I guess this guy never got the chance to get your advice, because he seems to have some serious yard bend going on with his balanced lug. The mast also seems to be flexing like crazy and his luff still looks sufficiently tight to me. Even though the sail is cotton, don't think for a minute that the sailmaker didn't design and build it with spar bend and a properly cut luff curve in mind. As I pointed out before, any good sailmaker should be considering and allowing for spar bend. (Photo from "Rushton and His Times in American Canoeing")
http://www.imagestation.com/picture/sraid51/pbc0b60741301838db66f02bd53c8a371/fc9f3f8a.jpg

D.D Quote:"Stiffen your mast as the first order of business."
From up here on my lofty perch, this seems awfully premature. Milli poses questions about boom and mast bend and their effect on the shape of a balanced lugsail on a boat that hasn't even been in the water yet. A boat designer who designs lug-rigged boats and a sailmaker who builds lugsails and who just built two of them last week both immediately suggest rigging the boat as specified and trying it out before making any changes - but you are dead certain that the first order of business is to stiffen the mast? Maybe the reason we didn't hand out that kind of advice is because we have to make a living at this stuff and people will hold us accountable for what we say.

[ 02-18-2003, 04:39 AM: Message edited by: Todd Bradshaw ]

[John Bell]

Craig, Todd, y'all play nice, OK? smile.gif

[Donn]

Thanks for that post, John. I never would have read this thread if you hadn't brought it to my attention. I usually avoid threads like this because there's just too much lingo that I don't recognize, but this one was too good to pass up. This is the kind of argument that belongs on the WB forum....and I increased my vocabulary a bit.

[Milli]

Thanks for the information (whoops---didn't mean to start an arguement...). I have been sailing my boat for a couple of season's and have been thoroughly delighted with the performance. My learning curve has been very steep with the rig and sail and I am questioning some things which may(?) help it sail better.

The foot of my sail has about 1 inch of round and I estimate my boom flexes about 3 inches. To me this suggests I may be pulling the draft out of lower part of the sail. Another thing I was considering was to lenthen the ties in the center of the boom to adjust for this ??

I have a 2:1 tackle for the tack line and get good luff tension---hence the bend in the boom. Possibly setting up a tack line arrangement that distributes the load over a few feet at the front of the boom could help ??? I also wonder if the flex in the boom could actually help with the tension as the boom is sort of "pre-loaded" like a bow ???

I am still not sure if a stiffer boom will make it better or if the effort will be worth it.

[Todd Bradshaw]

The thing that you are looking for is "foot camber" (draft in the area 12"-18" or so above the boom) which may or may not be formed by foot round. The amount of round that you can see when laying the sail out flat with no boom often depends upon how the sail is paneled and shaped and whether or not it's built to be laced onto the boom.

It's possible and not particularly difficult or unusual to build a sail with lots of foot camber, but a perfectly straight foot. Even so, it would be difficult to add the two to three inches of spar bend allowance that would normally be required on a sail and boat that size and still end up with only 1" of visible round, so my guess is that the allowance added to the sail (if any) doesn't match the bend of the boom. This puts us pretty much back at square #1 and your original assumption that the boom may be bending too much to get proper draft out of the sail (sure was the long, round-about way to get there huh?).

I would say that the next step would be to do a little testing under sail. I would add a temporary "draft stripe". That's just a fancy name for a horizontal strip of tape, about 15" up from the foot and running all the way across the sail. If you want something fancy, you can order draft stripe tape from places like Sailrite. If you want something cheap and easy, buy a roll or two of colored plastic tape, just don't leave it on the sail for more than a day or so since it might leave goo behind when you want to remove it.

The contrasting color of the tape will allow you to look up at the sail, while sailing, and see what kind of sail camber and airfoil shape you are getting across the foot on various points of sail. Off the wind with reduced mainsheet loads, it wouldn't be uncommon to be seeing the equivalent of one foot of draft depth for every ten feet of chord length (sail width at that level). Sheeted in hard, bending the spars and going upwind, it wouldn't be unusual to see the camber depth drop to half of that much (6" draft for 10' chord) or even less. For most dinghies, this type of variable camber range with amounts pretty close to those stated usually sails pretty well. Since your mast will be obstructing the camber on one tack, I'd do most of my testing on the other one just so that the picture is clearer.

If you find that the draft stripe is showing minimal foot camber (less than say 6" per 10' of chord on all points of sail) then you can be pretty sure that the boom flex is eating up your draft and it's time to start thinking about reducing boom bend. I would start by easing the downhaul, just to see how much tension you actually need for keeping the luff tight. Any more than that is just trying to stretch-out the luff fabric.

Once downhaul tension is adjusted to be adequate for a tight luff but not excessive, if the sail camber is still not there, it's probably time to rebuild the boom as it's easier than re-cutting the foot of the sail to match the bend.

[Ben Fuller]

Wow, this one heated up.....

To add confusion, seems to me I recall some of the Scottish fishing luggers had something radical at the top to reduce mast compression. I think it was a sheave block that worked a little like a ratchet block which would reduce compression on the mast considerably.

I think that there may be a difference between what happens with a balanced lug and a standing lug. With the latter any mast bend softens up the sail's luff immediately. Up to the point of mast bend, playing the downhaul moves draft around like using a cunningham on my bendy International Canoe rig. There when you pull on the cunningham the mast bends and draft moves into the curve and the sail flattens.

I have not played with a balance lug, but it strikes me that the downhaul is less loaded, and I would want the bit of boom from downhaul or mast cross to luff to be pretty stiff. Boom bending behind the mast would have less effect on luff tension. With a balanced lug the load seems to be spread more evenly.

When I got the sail cut for my high aspect lug rig, the sailmaker wanted bending stats on the spars which I gave him. Both are carbon and the yard does not bend much at all. In fact the sail went back as there was a soft spot up there that refused to go away. Turns out the yard was stiffer than anticipated. It is a bit more complex as the yard is in a sleeve. Mast is twice as stiff as the designer speced, and I have a pretty unforgiving low stretch multi part downhaul. When the mast starts bending it seems like it is time for a reef. But I am still going to get another layer of carbon on the mast; mistake we made was giving the mast too much taper. McKee in his Workig Boats of Britain shows tapers of 1 to .67 or .7 for luggers in contrast to 1. .5 or ,4 for jib headed sails.

For my rig mainsheet tension or leech tension does not seem to affect luff tension much, something that surprised me given the geometry of the rig. Perhaps it is the high peak. On the lower peaked balanced rig, mainsheet tension may have a bigger effect on luff tension.

A real fast way to tell if the boom bending is a problem is make it bend less by putting the mainsheet on a bridle, rather than tying it straight to the boom. And a couple of strips of unidirectional carbon fiber like West sells for repairs down the sides of a spar or on top of a boom are a real fast way of adding stiffness.

[ 02-18-2003, 10:31 PM: Message edited by: Ben Fuller ]

[Todd Bradshaw]

You are correct in thinking that the function of the downhaul line on a balanced lug can be quite different from it's function on a standing lug. On a balanced lug it has the function of tightening the luff, yet it is not a powerful direct pull like on a standing lug, since it is back from the luff a bit. It also keeps the whole sail from rotating due to both mainsheet tension and the yard having more length and weight aft of the masthead than in front of it. Without some sort of line or fitting to stop the rotation the peak would drop, the boom's tail end would drop to the deck and the portion of the boom that intersects the mast would move forward in front of the mast.

A downhaul line secured near the mast is one common simple way of stopping this rotation and at the same time increasing luff tension. Some boats have nothing more than a chunk of line hitched to the boom and a horn cleat on the mast and sail just fine. There are others that don't even use a downhaul line. Instead they have a parrel or jaw on the boom that bears against the aft side of the mast to stop the rotation and a Sunfish or iceboat-style mainsheet system which is basically self-luff-tensioning when sheeted in.

The harder you sheet in, the more downward pressure it puts on the boom and the more tension that puts on the sail's luff as well as flattening the entire sail. The sheet is deadened to the aft part of the hull or deck, runs up to a boom block near the boom's aft end, forward under the boom to another boom block just behind the mast intersection and down to either a deck mounted block and back to the sailor or it just hangs off of the boom block where the sailor can grab it. For simple dinghy rigs, this is often an ideal system. It is less prone to bending the boom in the middle (which is the biggest complaint with just hitching the sheet to the boom and sailing away) and it does a pretty good job of adjusting sailshape for various points of sail all by itself, so that the sailor doesn't even have to think about it.

A lateen sail is pretty much just a balanced lug with a closed forward end instead of a short vertical luff. The same forces and most of the same rigging principles that apply to one apply to the other. This type of along-the-boom sheeting system is standard on lateen rigged boats because it works so well. It will also work on most balanced lugs. It can even be combined with a separate boom-to-cleat downhaul line if you want to put a limit on the amount that the sail is allowed to "bag-out" when sailing off the wind with minimal sheet tension. I have one on our Sunfish and though not class legal for racing it really lets you tune-in just how much the boom can lift and how drafty the sail can get on a run.

This is why I suggested that perhaps Milli should try backing off on the downhaul tension if the sail seems too flat along the bottom before trying to rebuild the boom. I don't know how the boat's sheet is rigged, but it is quite possible that careful attachment of the mainsheet to the boom and easing the downhaul tension some may give good performance with less draft-robbing boom bend and no noticable decrease in performance due to luff sag.

[ 02-19-2003, 01:13 AM: Message edited by: Todd Bradshaw ]

[Milli]

Hmmm.....
I must say I have learned quite a bit regarding lug sails through this thread. Thanks to all who replied. I have a plan now to 'tweek' my rig which is exactly what I was after.

I like the idea of the draft tape as it will allow me to measure any adjustments I make. I am going to first try reducing the tension in the tack line and then possibly a tack-bridle arrangement to spread the load out a bit. I didn't think that the sheet could also be contributing to the boom bending. I curently have the sheet attached to the end of the boom so will try a sheet-bridle arrangement as well. Following that I might try the along-the-boom sheet arrangement. The last option would be to make a new stiffer boom.
Now if this snow would just go away and the lakes thaw...

[brian.cunningham]

Another one here appreciating the debate.

I could just stick a conventional rig on my boat, but I want to make my own sails so I can learn how to make sails.

[Tonyr]

Milli, If it's not an inappropriate question, where are you in Canada? It's not on your profile.

Regards, Tony.

[Milli]

I am located in Winnipeg.

[Tonyr]

Milli, Luggers are rare birds, at least around here. I do find mine an efficient rig on our water, in the sense that it is handy to use on what is basically a rowboat that sails, instead of a sailboat that rows. An easily driven boat does not need much of a sail to push her along very well, I find.

Regards, Tony.