# Thread: Broadseaming theory

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## Broadseaming theory

Hello everybody,

I am designing a small boat to build this summer. I will present the whole project here in several months, but it's still a work-in-progress now. Suffice to say, it is a low-budget project, and I'll have to make the sails myself, as a trip to our local sailmaker is completely unaffordable. Also, any kind of sailcloth is unavailable here, unless shipped from US (I live in Europe, Lithuania), so I'll use Tyvek. I already made 3 sails from this material, but all of those were flat-cut, with only some minor edge curves. For this project, I thought I'd be using darts to put the shape in, but after digging through this and some other forums, reading some opinions of experienced people, I decided it would be a cheap and dirty approach. Instead, I've decided to learn proper sailmaking, so I can design and make a fine sail (as good as possible with inferior materials).

I red several books on the subject, as well as articles and discussions (mostly on this forum). I think I know most of the basic stuff on designing and making a sail (not yet put that knowledge to a test, though).

There is just one thing that eludes explanation. It is broadseaming. Every book, every article I red explains perfectly how to draw, cut and sew those tapers, and the amount and location of them is always provided in boat plans. I understand the basic principle - the wider the broadseam, the more draft is put into sail, the curvier it is, the steeper entry of the luff, and so on. That's okay.

But no one, not even Emiliano Marino, explains how to connect desired sail shape with the amount and location of broadseams. There should be some kind of formula for translating 3D shape into broadseams, but nobody seems to know it. Marino gives a basic figure (1/2 inch for every 3 feet of distance from sail edge to the maximum draft line) with some allowances for fabric type, but that's just it. No explanation about how he arrived at those numbers.

An example. My design calls for standing lug (yes you can go lugnuts now!), 7.4m^2 area, cross-cut. Boomed, but loose-footed. Usually, sailmakers go for camber of 12-15% of chord length, but since I'll be using stretchy material, I think it would be wise not to exceed 10%, as the wind will do the rest. Maybe even as low as 5% in the upper part of the sail, since standing lug tends to twist bit more than other rigs. Deepest draft position would be about 40% throughout the whole sail. The deepest chord of the sail would be somewhere around 45% distance between tack and throat, above tack. Considering that this sail only has head attached to a spar (yard), and this yard will require compensation for bend on it's own, I think it would be best to neglect edge curves at all (except, of course, for concave in luff and leech, of course, as well as slight convex in foot for looks, but none of these add any draft). So, most of the shape will be put in by broadseams.

And for the past few weeks, I've been scratching my head - how do I convert this information into amount of broadseams? Broadseam depth is pretty much self-explanatory - up to the vertical deepest draft line. But what about width? Some of you might say this is more of an art than a science, but with my definite lack of experience, my attempt at "art" may be catastrophic. Anyways, I wish to learn, even if such subtleties won't matter much in the end.

I've tried to work out a formula myself, but there are just too many unknowns. For example, if I add 2cm wide, 30cm long broadseam on one of the seams, what will be the resultant draft at the end of the broadseam? Also, I have no clue if draft provided by adjacent broadseams is added up, or not. Also, how can I know if I need to put broadseam on every seam, or just every other one? If I'll broaden every seam opposed to every-other-one, will I have twice as much draft, or the same (with less stretched material)? And that just covers the luff tapers. What about leech tapers? How the heck do I calculate them?

I understand some of you know some eye-ball figures that "just work", but I want to understand this thing from a scientific standpoint. If someone, anyone (especially you, Todd...) could help me out, it would be great. My head hurts after weeks of trying to figure it out, and there are few places left I have to turn to for help.

Thank you in advance!

2. ## Re: Broadseaming theory

I don't think that you can broad seam a cross cut sail, I think that it can only be used with a vertical cut sail, on the seams at the head.

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## Re: Broadseaming theory

Originally Posted by Peerie Maa
I don't think that you can broad seam a cross cut sail, I think that it can only be used with a vertical cut sail, on the seams at the head.
Um... What? Half of article 6 in Marino's book explains broadseams on the cross-cut sail. They are definitely used. Unless I misunderstood you?

P.S. Quote from the book, page 263:

"With few exceptions, only crosscut sails lend themselves well to extensive broadseaming at the luff."

4. ## Re: Broadseaming theory

Broad seaming is simply putting the curve in by changing the overlap of the panels from thinner (where the belly should be) to wider overlap approaching luff and leech. It's seriously easier than cutting long gentle curves in dacron as it leaves the finished strong edges. With Tyvek this matters less and if you can measure the curve, stake out a batten holding the Tyvek in place, and cut to that, then an even thickness seam exactly on width of your double stick tape wide will be easier to lay out. So, depends on how you like to work.

5. ## Re: Broadseaming theory

You need to hear from Todd Bradshaw. Maybe send him a PM.

Cheers,

Bobby

6. ## Re: Broadseaming theory

(1)Your draft figure is awfully high for a standing lug unless the boat is a really fat one that needs lots of power to push it through a chop. 10% draft to chord width would be a lot more common for most boats.

(2) Rather than just being there to add draft, the main function of broadseaming is to position the draft. It moves the excess cloth created by edge rounds away from the edges and toward the middle of the sail where it can create draft.

(3) Your sail's head needs round - both for draft and also (usually more so) to compensate for yard bend in use.

(4) Other than some junk sails and most batwings, just about every other sail is broadseamed - vertical cuts at the head and foot, cross-cuts at the luff, along the head if it has one and usually just slightly along the leech. This is also true of computer-cut sails, only they do it differently. Instead of leaving the fabric panel widths constant and varying the seam widths, the computer leaves the seam widths constant and cuts curved edges on the panels. The resulting shape is the same, but constant seam widths make it easier for assemblers to sew sails together at a factory without needing to know anything about shaping sails.

(5) Yes, there is very little published about broadseaming in terms of facts and figures. You are likely to find something like "increase the seam width 1/2" for every 30" of broadseam length for medium firm cloth, a bit more for firmer fabric and a bit less for softer fabric. If the sail is cross-cut with a tack seam, broadseam that seam at about twice the normal rate". Keep in mind that cloth wider than 36" is a fairly new thing. Most of the books were written with 36" wide panels in mind and broadseams on each panel seam. If your panels are wider or narrower than 36" you would want to adjust your broadseams accordingly to end up with the same total amount. For 12" panels, for example, you could either broadseam every third seam, or broadseam them all but with much narrower increases. For 54" panels you would need a 3/4" seam width increase per 30" of broadseam length to generate the target figures, though wide panels and really fat broadseams don't tend to produce sails with particularly smooth shape.

(6) Personaly, I'd rather cut lugsails vertically, and I think it's probably a better bet for a beginner as well. I think laying out the broadseam zones is more straightforward and it gives me a luff that can usually be cut dead straight and easily reinforced to handle high downhaul tension without distortion and without it acting as much like a Cunningham and shifting the draft forward. If you really do need 12-15% draft, it would likely be easier to generate with a cross-cut with a big tack seam, but otherwise I think you have a better chance of getting things right with a vertical cut, a straight luff, and a couple of triangular broadseam zones at the top and bottom.

The "art" part of broadseaming for those of us who don't computer-plot our sails, is mostly just a matter of having done it enough times and seen the results that we don't have to think about it too much. Maybe someday somebody will write a book that breaks it all down into logical formulas, but I wouldn't hold my breath waiting for it. It would be a massive undertaking (and the payback for writing boating books isn't very good). Marino's book was already a massive undertaking and is very well done, but even so there is much that it doesn't cover thoroughly. In a day when sail sales are driven more by price than quality and most are built in offshore factories by assemblers connecting computer generated pieces, rather than by sailmakers, the likelihood that somebody is going to be able to justify putting out a truly thorough DIY sailmaking book is pretty slim.

7. ## Re: Broadseaming theory

Todd's the man. Lot's of other folks know this stuff, but none share so generously and concisely.

A big thanks from all of us.

Allan.

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## Re: Broadseaming theory

Thank you everybody for your answers. I appreciate you helping me in this complicated task.

I believe it'll be best if I present my boat a little, so that it becomes clear what is expected of the sail.

This is 2 person, 3.3m stitch&glue lightweight boat, designed for cruising in very specific weather conditions of my country. It is meant to be car-topped, hence, the hull weight is 30kg, and fully rigged weight is around 45kg. Maximum displacement is 210kg.

I'd expect any experienced sailor would immediatelly tell me that 7.5m^2 (80ft) sail is way oversized for such a small and light boat with very little initial stability. It would be true in "normal" conditions most people sail in. However, my waters have a very specific weather pattern.
I'm doing all of my sailing in our glacier-origin lakes, which are narrow and branched, instead of the usual round or oval. Therefore, there are very little open spaces. What's more, those lakes are surrounded by forests and hills. This particular combination means that wind is totally crazy when it comes to direction and consistency. 90% of the time, it never exceeds 0-2 knots. When there is more wind, it is the same 0-2 knots with gusts up to 25 knots. Wind direction can change 180° in 20 seconds. So, most of the time, you're searching for ripples in the water, following narrow wind streams, manouvering between close shores of those lake branches, and keeping an eye out for gusts which can capsize boat in seconds.
It is actually very challanging, I've sailed in those conditions for the past 3 years, and every boat I had was under-powered because of lack of wind. Once I actually sat for 10 minutes in the same spot, robbed of wind, and then a gust came, broke some branches of a tree nearby, and almost capsized me. Yes, it is quite unbelievable until you experience it.

This is why I chose massive sail and a lightweight boat - to catch those few knots of wind, while utilizing wind-spilling capabilities of standing lug to survive gusts. Lug is also very easy to set up and take down, while providing lots of manageable sail area.

So, back to the sail.
Here is the general plan (luff made straight as per Todd's recommendation). Boat for scale. Boards not included in this sketch, of course, as well as spars (boom and yard):

(Please don't mind those stars, they mean nothing)

Dimensions are as follows:

Luff: 202.1cm (6ft 7.56in)
Head: 290cm (9ft 6.96in)
Leech: 483.7 (15ft 10.43in)
Foot: 260cm (8ft 6.36in)
Luff/head angle: 36.65°

Head round: 8.7cm (3.42in), 3%, located at 40% (for yard bend)
Luff concave: 6.54cm (2.57in), 1.35% (as per Emiliano Marino's recommendation of 1:74 ratio), located at 45%
Foot round: 5.09cm (2in), 2% (Marino recommends not to exceed 3%, so I've decided to stay on the safe side), located at 40%

Area: around 7.5m^2 (80ft) (still not final)

Originally Posted by Todd Bradshaw
(1)Your draft figure is awfully high for a standing lug unless the boat is a really fat one that needs lots of power to push it through a chop. 10% draft to chord width would be a lot more common for most boats.
I believe you might have misunderstood me there. That's what I meant - that standard 12-15% would too much for Tyvek, so I'm aiming at 10%.

(3) Your sail's head needs round - both for draft and also (usually more so) to compensate for yard bend in use.
How much should I add for yard bend alone? My yard will be 300cm long (9.84ft), with maximum diameter of 4.5cm (1.77in), that is 1.5% of it's length, with tapering of 75% at ends, that is 3.4cm (1.34in). Right now, I added a head roach of 3% of it's length to compensate for yard bend. Is that close enough?

(6) Personaly, I'd rather cut lugsails vertically, and I think it's probably a better bet for a beginner as well. I think laying out the broadseam zones is more straightforward and it gives me a luff that can usually be cut dead straight and easily reinforced to handle high downhaul tension without distortion and without it acting as much like a Cunningham and shifting the draft forward. If you really do need 12-15% draft, it would likely be easier to generate with a cross-cut with a big tack seam, but otherwise I think you have a better chance of getting things right with a vertical cut, a straight luff, and a couple of triangular broadseam zones at the top and bottom.
All right. I've re-sketched my sail with vertical seams. Since Tyvek is sold in 1.5m rolls, I think I'll slit that in half to 75cm (29.52in) for more draft control. Also, closer to the traditional 36in cloth width. So, seams run like this now:

I can move them forward or aft a bit, but not sure if I need to. I'm trying to keep sufficient cloth outside sail's perimeter for secondary cutting (after broadseams are done), and for edge overlaps, of course.

(5) Yes, there is very little published about broadseaming in terms of facts and figures. You are likely to find something like "increase the seam width 1/2" for every 30" of broadseam length for medium firm cloth, a bit more for firmer fabric and a bit less for softer fabric. If the sail is cross-cut with a tack seam, broadseam that seam at about twice the normal rate". Keep in mind that cloth wider than 36" is a fairly new thing. Most of the books were written with 36" wide panels in mind and broadseams on each panel seam. If your panels are wider or narrower than 36" you would want to adjust your broadseams accordingly to end up with the same total amount. For 12" panels, for example, you could either broadseam every third seam, or broadseam them all but with much narrower increases. For 54" panels you would need a 3/4" seam width increase per 30" of broadseam length to generate the target figures, though wide panels and really fat broadseams don't tend to produce sails with particularly smooth shape.

The "art" part of broadseaming for those of us who don't computer-plot our sails, is mostly just a matter of having done it enough times and seen the results that we don't have to think about it too much. Maybe someday somebody will write a book that breaks it all down into logical formulas, but I wouldn't hold my breath waiting for it. It would be a massive undertaking (and the payback for writing boating books isn't very good). Marino's book was already a massive undertaking and is very well done, but even so there is much that it doesn't cover thoroughly. In a day when sail sales are driven more by price than quality and most are built in offshore factories by assemblers connecting computer generated pieces, rather than by sailmakers, the likelihood that somebody is going to be able to justify putting out a truly thorough DIY sailmaking book is pretty slim.
Well, I understand that. But aren't there any more specific guidelines? You've now seen my sail. I've chosen the shape, the roundings, seam locations. How can I now know how much broadseaming and edge curves should I add so I can have 10% draft in my sail? How do I know if I need to broadseam every seam, or just every other? The guidelines you and Marino provided, like "increase the seam width 1/2" for every 30", are they meant for 10% draft, or 12%, or 15%? How do I figure that out?

I thank you very much for the idea to adjust those guidelines proportionally according to the cloth width, but how do I know what kind of sail draft are they meant for in the first place?

And I'm sorry if I appear obbsessive in this matter, but I really want to understand, to learn. I can live with no formula's being out there for sailmaking, but I can't still connect these techniques (broadseaming, edge curves, etc) with final sail shape in my head.

P.S. I just red this post, so you don't have to repeat anything you've said there, it's explained nicely!
Last edited by Laukejas; 02-07-2015 at 12:52 PM.

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## Re: Broadseaming theory

After reading that post, I think I should use narrower panels. Maybe it would be better to slit 1.5m Tyvek rolls into 50cm (19.68in) panels.

Here's a sketch with those panels. I've also added broadseaming areas, with tips being at 40% of chord line length. I've also tried to align panels so that seams intersect the tips of broadseaming area triangles. Please tell me if I'm working in a right direction...

10. ## Re: Broadseaming theory

Before I forget....your figure for hollowing the luff is way too big. It is a percentage of luff length and in this case it would come out about 1.08". Whether or not you actually need to hollow such a short luff is a toss-up. I generally don't and find that once you get the luff well reinforced on small lugsails with short luffs, it is too stiff for the downhaul tension to pull the curve out and make it straight and/or tight, which is what's supposed to happen in use. For this reason I don't add luff curve to lug luffs for draft either. A convex luff will flap and is really annoying. A slightly hollowed luff can be helpful in maintaining good luff tension (countering luff sag, the same way we do on jibs) if it is a long luff, but it usually has to be ten feet or better before I start worrying about sag. However, I don't work in Tyvek and don't know how it stacks up in terms of dimensional stability compared to Dacron (especially long term stability). It can't hurt to cut a little hollow into the luff - just don't go crazy with it.

How do you insure that you are creating 10% draft on a vertically cut lugsail? Unless your brain can juggle a whole lot of figures and essentially see in measured 3-D, you don't. Computer programs can do this, but most of us can't. Instead, we build to dimensions that have been proven over time and which seem to work pretty well for average, typical sails. If for some reason the boat is unusual and we think we need to change things a bit, it is generally done seat-of-the-pants-style based on our experience. Yes, this is horribly unscientific, but for one-off hand-builds without the benefit of high-powered software, this is reality.

Other dimensions: Your head round looks about right. Of that 3.42" about 1.5" will go for draft production and the rest to allow for in use yard bend. There really is no right answer here. The bend in the yard is constantly changing and our allowance for it is always a compromise. Sometimes it will be too little, other times too much and at least part of the time, just about right. That's about what I would build into that sail and I usually suggest that my customers follow Iain Oughtred's suggestions for yard diameter and taper, which seem to work pretty well - not too heavy and not too whippy (max diameter 1:64 to 1:60 of length, tapered to 82% at the heel and 62% at the peak). Your leech hollow and foot round look fine.

Panel width: You are correct that narrowing the panels will work better. More and smaller broadseams will produce a smoother shape. If we assume that Tyvek may have similar stability to 4 oz. Dacron (at least when the Tyvek is new - and it might) then I suppose we should stick with the old standby 1/2" broadseam added per 30" of broadseam length for 36" fabric. I drew the sail up with 18" panels, which is how I would build it, and I would be broadseaming all seams in the broadseam zones at half that rate (1/4" per 30" of broadseam length). It looks like this.

You can cheat a little bit, widening the leech panel a bit to allow excess for the leech hem turnovers and widening the luff panel to eliminate that tiny panel seam at the tack corner. It's mostly going to be covered by the luff tape and tack patches anyway. The broadseam zones were just put in by eye from experience, the same way I would do it on the floor. That experience tells me that if I do it like that and broadseam at the normal rate, it produces a lugsail with about the amount of draft we're looking for and they sail pretty well. Again, horribly unscientific - but there has to be some reward for all those years crawling around on a hardwood floor shaping these things. When the finished product sets this well, being unscientific seems to be acceptable.

This is the same balanced lug hung up in my back yard for inspection when finished and if you look closely you can see the broadseams.

It is not important that the tips of the broadseam zones are on seams. Other than the sail's chord shape, those spots have no shape. The broadseams are just beginning in those areas and not really doing anything yet. At the sail's head and foot edges we do want to do something different though. A broadseam should be a smooth, straight, tapered increase in seam width, but for maybe the last 10% of its length as we near those edges, we flare it a little bit. We increase our rate of overlap, which tends to give the edge a little bit of a cupped shape (not too much, which would curl the edge, but just a little bit). This both helps keep the edge tight to resist flapping, and also gives us a little bit of the old end-plate effect (helps keep air from sneaking around from the high pressure side of the sail to its low pressure side - robbing us of power).

I'd probably use a rolled hem on the leech with Tyvek (fold it once about 3/4" and then one more time) for strength and stretch resistance. Small lug luffs around here usually get double luff taped. I fold a 2" wide strip over the panel fabric, and then fold a 3" strip over the top, making the luff five layers thick everywhere, plus corner patches where needed (tack, throat, reef tacks). Those areas will end up about nine layers thick. This is done to compensate for the constant and rather high downhaul tension that these sails normally operate under. They can also be roped for reinforcement, though I don't know how well Tyvek will hold big stitches. If it helps, I have a photospread of making a lugsail here.

http://s1303.photobucket.com/user/To...?sort=9&page=1
Last edited by Todd Bradshaw; 02-07-2015 at 10:09 PM.

11. ## Re: Broadseaming theory

Todd is right.

But as far as "books for amateur sailmakers", of which there are so very few, you might be able to check out Jim Grant's from Sailrite. I don't know if lugsails are in there, and mine are still unorganized from the latest move, but they were written with a lack of computers in mind. They might help.

12. ## Re: Broadseaming theory

He doesn't mention four-sided sails, but there is plenty in those little booklets (Grant's "Sailmaker Series) that is worth knowing and which can apply to any sail building project. In terms of just "Measure this and do that using this formula" I think they are probably the best amateur sailmaking books ever written.

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## Re: Broadseaming theory

Originally Posted by Todd Bradshaw
Before I forget....your figure for hollowing the luff is way too big. It is a percentage of luff length and in this case it would come out about 1.08". Whether or not you actually need to hollow such a short luff is a toss-up. I generally don't and find that once you get the luff well reinforced on small lugsails with short luffs, it is too stiff for the downhaul tension to pull the curve out and make it straight and/or tight, which is what's supposed to happen in use. For this reason I don't add luff curve to lug luffs for draft either. A convex luff will flap and is really annoying. A slightly hollowed luff can be helpful in maintaining good luff tension (countering luff sag, the same way we do on jibs) if it is a long luff, but it usually has to be ten feet or better before I start worrying about sag. However, I don't work in Tyvek and don't know how it stacks up in terms of dimensional stability compared to Dacron (especially long term stability). It can't hurt to cut a little hollow into the luff - just d
I'm sorry, it was a typo in a hurry. I meant leech hollow, but wrote luff instead for some reason (English is not my native language, terms still mix up at times). I'll cut luff straight, that much is clear, but thanks anyway for pointing it out!

Originally Posted by Todd Bradshaw
Other dimensions: Your head round looks about right. Of that 3.42" about 1.5" will go for draft production and the rest to allow for in use yard bend. There really is no right answer here. The bend in the yard is constantly changing and our allowance for it is always a compromise. Sometimes it will be too little, other times too much and at least part of the time, just about right. That's about what I would build into that sail and I usually suggest that my customers follow Iain Oughtred's suggestions for yard diameter and taper, which seem to work pretty well - not too heavy and not too whippy (max diameter 1:64 to 1:60 of length, tapered to 82% at the heel and 62% at the peak). Your leech hollow and foot round look fine.
I thought that yard should have proportional taper... I'll adjust per your recommendation.

Originally Posted by Todd Bradshaw
Panel width: You are correct that narrowing the panels will work better. More and smaller broadseams will produce a smoother shape. If we assume that Tyvek may have similar stability to 4 oz. Dacron (at least when the Tyvek is new - and it might) then I suppose we should stick with the old standby 1/2" broadseam added per 30" of broadseam length for 36" fabric. I drew the sail up with 18" panels, which is how I would build it, and I would be broadseaming all seams in the broadseam zones at half that rate (1/4" per 30" of broadseam length). It looks like this.
According to the Emiliano Marino, 1/2'' per 30'' of broadseam length is meant for medium-firm dacron (middle ground between per 24'' for soft and per 36'' for stiff). I suppose that means that 4oz. Dacron is not the softest one out there, right? Or are you using different proportions than Marino? Because I thought I should use recommendation for softest cloth. Sorry if my questions are stupid. Just trying to understand your advice

Those are very interesting broadseam areas you've drawn. When I drew mine, I drew them with relation to the maximum draft line, which goes around 40% of the chord length throughout the whole sail. It looks like this, on the left (dashed line is the maximum depth chord). On the right, I've shown how I connected broadseam area triangles with that depth curve (in blue). Your suggested broadseam area is marked in red:

You've drawn broadseam areas deeper, with bottom triangle more towards leech, and upper triangle more towards luff. I'm wondering, why? Please don't take that as questioning of your judgement, I trust your experience way more than my amateurish attempts, it's just that I'm trying to compare so that I can understand your reasoning, and to see where my estimations are off. I hope that's okay.

Your sails are truly beautiful. So simple, yet so right. I can't help but notice, though, that this lugsail appears to have this small cloth panel near the tack, the one you recommended me to avoid! Or maybe my eyes deceive me.

I'll have to plan a little more to finalize the cloth width and location. There has to be some left for hems and for secondary cutting!

Originally Posted by Todd Bradshaw
I'd probably use a rolled hem on the leech with Tyvek (fold it once about 3/4" and then one more time) for strength and stretch resistance. Small lug luffs around here usually get double luff taped. I fold a 2" wide strip over the panel fabric, and then fold a 3" strip over the top, making the luff five layers thick everywhere, plus corner patches where needed (tack, throat, reef tacks). Those areas will end up about nine layers thick. This is done to compensate for the constant and rather high downhaul tension that these sails normally operate under. They can also be roped for reinforcement, though I don't know how well Tyvek will hold big stitches. If it helps, I have a photospread of making a lugsail here.
Interesting. I've always used simple hem (just fold over once) on Tyvek, 2'' wide (because that's the width of double-sided sticky tape I used). I also used 4mm (3/16'') polyester rope around the perimeter, inside this hem. I guess rolled hem makes more sense, but what about perimeter rope? Would you use it? I guess it adds strength, but I'm sort of worried that it makes leech a bit round, instead of sharp, and disrupts the airflow. What would you do if you made a sail from Tyvek?

Just one more little question, if I may. How do you usually slit the cloth into narrower widths? I can think of two ways: lay it out, measure from the edge at each end end, and slit along the length, or roll the cloth tightly, measure from the end of the roll, and slit through all the layers at once?

And a huge thank you for helping me out so far. I can see why people on this forum appreciate your input so much. You are very generous with your time and knowledge. I wish there were more people like you, in every field.
Last edited by Laukejas; 02-08-2015 at 07:00 AM.

14. ## Re: Broadseaming theory

According to the Emiliano Marino, 1/2'' per 30'' of broadseam length is meant for medium-firm dacron (middle ground between per 24'' for soft and per 36'' for stiff). I suppose that means that 4oz. Dacron is not the softest one out there, right? Or are you using different proportions than Marino?
Most 4 oz. Dacron is classified as "medium". There are a couple fabrics in that weight range which are softer (Fleetboat Dacron and "Finn" grade for example) and a few that are firmer in tempered racing grades, but the aim of most 4 oz. is general purpose medium-firm fabric for dinghy sails. The only Tyvek I have in the house are some mailing envelopes, and upon inspection they seem at least fairly similar to typical 4 oz. cloth and more stable than the soft grades would be when stressed on the bias (which they really don't actually have, being non-woven). What the Tyvek would be like in terms of stability after a few sailing excursions is hard to predict and having never tried it for sails, I can't say.

Those are very interesting broadseam areas you've drawn. When I drew mine, I drew them with relation to the maximum draft line, which goes around 40% of the chord length throughout the whole sail. It looks like this, on the left (dashed line is the maximum depth chord). On the right, I've shown how I connected broadseam area triangles with that depth curve (in blue). Your suggested broadseam area is marked in red:
I usually go more like 45% than 40% on most lugs. If it's a really high aspect sail for a fast hull, I might go a bit farther forward, but since almost every sail I build is a one-off, I tend to stick fairly closely to what has always seemed to work for me. I typically think of my broadseaming curve as terminating maybe 45%-50% aft along the head, rather than running all the way up to the peak as you have drawn yours. In terms of generating power, I'd rather have the draft correct at the throat level, where we have more productive sail area, than up higher. Your method tends to position maximum draft awfully far back at the level of the throat and upper luff for my taste. Does everyone do it that way? Probably not. Is it the only way that sets and sails well? Probably not, but again when almost every sail is a new design project from scratch, I tend to stick with what has worked well for me.

I can't help but notice, though, that this lugsail appears to have this small cloth panel near the tack, the one you recommended me to avoid!
Yes, it does. For sails like that I split the fabric into thirds and that becomes the panel width. Whether it is more economical to add that small seam and a small panel or cut a piece that's a few inches wider and not need the extra seam just depends on what sort of scrap pieces I have left after paneling the rest of the sail. If I have to chop into an additional yard or two of expensive fabric to get that little extra-wide piece, then it's usually more economical to add the seam and do that chunk with the normal panels. Since Tyvek is so cheap and so wide, you shouldn't have to worry about fabric cost and can eliminate the seam.

Interesting. I've always used simple hem (just fold over once) on Tyvek, 2'' wide (because that's the width of double-sided sticky tape I used). I also used 4mm (3/16'') polyester rope around the perimeter, inside this hem. I guess rolled hem makes more sense, but what about perimeter rope? Would you use it? I guess it adds strength, but I'm sort of worried that it makes leech a bit round, instead of sharp, and disrupts the airflow. What would you do if you made a sail from Tyvek?
The wider the hem, the harder it is to get a smooth roll around the curve of the leech, and I'm looking for the smoothest leech (and "wind-exit") that I can produce, while trying to maintain adequate strength and stretch resistance along that edge. A single fold of Tyvek seemed a little flimsy to me, though having never built a Tyvek sail, or had a chance to see how they hold up over time, it might be OK. If a vertically cut sail stretches along the leech and starts to flutter back there in use, the only way to fix it is to re-cut the entire leech with a deeper hollow. This is usually a real pain in the butt repair, especially with corner patches and reef clew patches and rings to deal with in the process. I'd just as soon do my best to avoid that from the start. Roping the leech makes too much of a bump there for my taste. They used to do it on junk sails, but it is quite rare on most other types.

How do you usually slit the cloth into narrower widths?
I usually panel the sail over the lofting with full width fabric, rough-cutting the various chunks a bit big, then cut each chunk into the narrower panel widths. I lay them out on the floor on a piece of thin plywood, measure and mark them, and split them with a six foot metal ruler and a knife. It's a pain in the ass and one of my least favorite parts of the process. Some sailcloth manufacturers have custom heat-slitting available, but it is expensive and you usually have to buy full rolls (like 50 yards) of cloth at a time. For a small, low budget operation like mine, and sails built with varying colors and panel widths, that doesn't work for me. I noticed that my local big box hardware store can now get 4' x 8' sheets of 1/8" polyethylene at a reasonable price, so this spring (or whenever my heart surgeon says it's OK to pick up something heavier than ten pounds) Ill treat myself to a new cutting board and eliminate the plywood splinters.

I did once try rolling the Dacron very tightly on a tube and running it through the band saw to cut panel widths and edge tape widths. It almost worked and actually did kind of a nice hot-cut edge. No matter how carefully I fed it though, when rolled out, the edges had enough random waviness that the idea was rejected and it was back to hand-cutting.

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## Re: Broadseaming theory

Originally Posted by Todd Bradshaw
Most 4 oz. Dacron is classified as "medium". There are a couple fabrics in that weight range which are softer (Fleetboat Dacron and "Finn" grade for example) and a few that are firmer in tempered racing grades, but the aim of most 4 oz. is general purpose medium-firm fabric for dinghy sails. The only Tyvek I have in the house are some mailing envelopes, and upon inspection they seem at least fairly similar to typical 4 oz. cloth and more stable than the soft grades would be when stressed on the bias (which they really don't actually have, being non-woven). What the Tyvek would be like in terms of stability after a few sailing excursions is hard to predict and having never tried it for sails, I can't say.

I usually go more like 45% than 40% on most lugs. If it's a really high aspect sail for a fast hull, I might go a bit farther forward, but since almost every sail I build is a one-off, I tend to stick fairly closely to what has always seemed to work for me. I typically think of my broadseaming curve as terminating maybe 45%-50% aft along the head, rather than running all the way up to the peak as you have drawn yours. In terms of generating power, I'd rather have the draft correct at the throat level, where we have more productive sail area, than up higher. Your method tends to position maximum draft awfully far back at the level of the throat and upper luff for my taste. Does everyone do it that way? Probably not. Is it the only way that sets and sails well? Probably not, but again when almost every sail is a new design project from scratch, I tend to stick with what has worked well for me.
Understood, thank you. I modified my design. I though that I should move maximum draft a bit further because Tyvek is stretchy, and the wind will push sail camber back. But if you say so, I trust you!

The wider the hem, the harder it is to get a smooth roll around the curve of the leech, and I'm looking for the smoothest leech (and "wind-exit") that I can produce, while trying to maintain adequate strength and stretch resistance along that edge. A single fold of Tyvek seemed a little flimsy to me, though having never built a Tyvek sail, or had a chance to see how they hold up over time, it might be OK. If a vertically cut sail stretches along the leech and starts to flutter back there in use, the only way to fix it is to re-cut the entire leech with a deeper hollow. This is usually a real pain in the butt repair, especially with corner patches and reef clew patches and rings to deal with in the process. I'd just as soon do my best to avoid that from the start. Roping the leech makes too much of a bump there for my taste. They used to do it on junk sails, but it is quite rare on most other types.
All right, I'll dump the perimeter rope then. Never liked it anyway. But what about luff? Can I go without rope there too, only adding these numerous layers of Tyvek like you suggested? (I also have an idea to put a strip of webbing inside). Luff would be less bumpy without the rope too, giving better smoother airflow.

I usually panel the sail over the lofting with full width fabric, rough-cutting the various chunks a bit big, then cut each chunk into the narrower panel widths. I lay them out on the floor on a piece of thin plywood, measure and mark them, and split them with a six foot metal ruler and a knife. It's a pain in the ass and one of my least favorite parts of the process. Some sailcloth manufacturers have custom heat-slitting available, but it is expensive and you usually have to buy full rolls (like 50 yards) of cloth at a time. For a small, low budget operation like mine, and sails built with varying colors and panel widths, that doesn't work for me. I noticed that my local big box hardware store can now get 4' x 8' sheets of 1/8" polyethylene at a reasonable price, so this spring (or whenever my heart surgeon says it's OK to pick up something heavier than ten pounds) Ill treat myself to a new cutting board and eliminate the plywood splinters.

I did once try rolling the Dacron very tightly on a tube and running it through the band saw to cut panel widths and edge tape widths. It almost worked and actually did kind of a nice hot-cut edge. No matter how carefully I fed it though, when rolled out, the edges had enough random waviness that the idea was rejected and it was back to hand-cutting.
Great points to consider. I'll cut it like you did on plywood, then.

I'd just like to ask few more small questions, and then I won't take any more of your time. A bit off-topic, but I hope that's okay.

Since you had a lot of experience with lugs, can you tell me how can I estimate the best halyard attachment position on the yard, and at what angle will the halyard go from masthead block/sheave to the yard? Right now, I've chosen the "usual" position of 40% from yard's heel, but people say it might vary. For the angle, I shot for 45° to the mast, but that is a shot in a dark, a figure I chose from observation of various lugsails on the internet.
The reason I ask this is because if my estimates are wrong, the halyard attachment point on the yard might need to be moved somewhat, and the halyard/mast angle may also be different, and that will may shift the sail forward or backward a bit, messing up sail balance, creating windward or leeward helm (I'm very, very afraid of leeward helm. I experienced it once, and that is something no man should ever experience). Right now, the boat is balanced with CE being 1% aft of CLR for slight weather helm (mostly just to be sure it's on the right side), as I plan to sail this boat with zero heel most of the time. However, if sail needs to be shifted forward as a result of different halyard attachment location or halyard/mast angle, it'll all mess up.

And another question. Messing around with Tyvek is okay for a begginner like me - mistakes cost less - but looking at your sails, at that beautiful fabric just makes my heart pound and hands start to shake. I'd love to get my hands on true sailcloth - any kind of sailcloth - and maybe, after few more Tyvek sails for practice, have a go with proper material.
However, as I mentioned, I looked hard for European sources for sailcloth, and it seems that there are none. There are several re-sellers who ship from US, but their prices are about the same as if I were to ship the cloth myself. And that shipping can cost two to three times as much as the fabric itself, and I certainly don't need full rolls for my small projects.
Todd, you are a certainly knowledgeable in sailmaking. I take that you are the head of "Addiction Sailmakers". I know you do your things in USA, but maybe, just maybe, you know some manufacturers of sailcloth in Europe, preferably near Lithuania (by the Baltic Sea)? There must be something, but after many attempts at Google, I've never found anything.
If not, what sailcloth source would you recommend in USA, that has lowest cloth price + shipping price to Europe combo? I'm not racing, so I certainly don't need top-of-the line stuff. I probably wouldn't be able to afford to ship from USA right now, but maybe sometime...

16. ## Re: Broadseaming theory

Understood, thank you. I modified my design. I though that I should move maximum draft a bit further because Tyvek is stretchy, and the wind will push sail camber back. But if you say so, I trust you!
Remember, I don't build, and have never built Tyvek sails, so my impressions of its stretch and stability are just based on handling samples of it. Whether or not I would modify a sail's shape to allow for excess stretch would have to be based on real life examples. For unusually stretchy cloth, I would still probably change the broadseaming rate as a first attempt rather than trying to guess how much to shift the draft.

All right, I'll dump the perimeter rope then. Never liked it anyway. But what about luff? Can I go without rope there too, only adding these numerous layers of Tyvek like you suggested? (I also have an idea to put a strip of webbing inside). Luff would be less bumpy without the rope too, giving better smoother airflow.
If one layer is strong enough for the panels, five should be OK for the luff. Webbing could also be done, but probably isn't needed.

From what I can tell the biggest variable in the halyard angle is probably the amount of mast that sticks up above the mast/yard intersection. The less excess mast you have above the yard, the less that angle can vary. One thing about lugs is that once you hoist one, it becomes pretty obvious that you are hoisting a contraption up a mast with few attachment points compared to other sail types. It's kind of like flying a kite from a stick. There are various methods with parrels, different ways to rig the halyard and even hardware that can be added to the mix to help fix it in position if needed - but even so, I think it's wise to expect to need to do some experimentation with the halyard's position on the yard once you actually start your sea trials. The figures and formulas that we use for drawing sailplans and fitting them on hull drawings using centers of effort, centers of lateral plane, lead etc. are just design guidelines. Much of the time that you are actually sailing the boat, they either won't apply or will be inaccurate. They do help us get the design figured out, so that we have something to build to, but the final word is always testing and adjusting out on the water. Even America's Cup syndicates with nearly unlimited funds and massive computer design and performance power at their disposal can't always tell what will work best until they get out on the water to test and tweak it. As nice as it might be to be able to figure out all these factors on the drawing board before building the boat, it seldom works that way in real life, and it is certainly possible to "over-think" some of this stuff ahead of time and drive yourself crazy.

I take that you are the head of "Addiction Sailmakers".
The head, the tail and everything between them

preferably near Lithuania (by the Baltic Sea)?
My wife is a molecular biologist from Latvia.

Contender Sailcloth is made in Europe and they have outlets in The Netherlands, France, Italy, Germany, Spain, The UK and Sweden. They make an all purpose 4 oz. cloth for small boats and their premium "Supercruise" also in 4 oz. weight. Both are also available in 5.4 oz. for slightly bigger sails.

Dimension Polyant Sailcloth is another good one. They are headquartered in Germany with outlets in France, The UK, Italy and Russia. They build a full line of woven fabrics and also some very neat Mylar laminates.

Challenge Sailcloth and Bainbridge International (both American-based) also have outlets in Europe.

Most of these companies deal wholesale, rather than retail (at least they do over here). Rather than trying to set up a wholesale account to build a couple of sails, the best bet may be checking with sailmakers reasonably close to you to see if they will add a few yards of cloth for you to one of their orders. Adding a retail mark-up, handing a small roll of cloth over the counter and collecting a check is pretty easy money for most sailmakers.

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## Re: Broadseaming theory

There is a UK seller of Dacron sailcloth. He lists his materials on eBay. Good man.

http://www.ebay.co.uk/sch/m.html?_od...cloth&_sacat=0

He stocks end of roll, or rolls with faults in them somewhere. These rolls are of no use whatsoever to the sailmakers but are perfect for guys like us who make a single sail or just a couple of sails. Couple of years ago I built a sail the same size as yours for about £40. He did prefer you call in to see him but hopefully since you are a long way away he will ship to you.

Brilliant source of sailcloth. You need double sided basting tape. You also need the proper star grommets. Try to buy these from a friendly local sailmaker. They are usually helpful and slightly amused that you are trying to make a sail. Hardest thing to get hold of was the punch to close the grommets. Again local sailmaker lent me their old set for the afternoon. You can buy the tools but you need three for the different sizes and that will be too expensive just for the odd sail.

Brian

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## Re: Broadseaming theory

I have gone to using D rings and webbing for attatchments rather than grommets, mainly for the reason Brian mentioned that a set of different size punches and setting tools is a big investment for someone making a one-off sail. I have had a friendly sailmaker set some corner eyes in a hydraulic press, but given the cost of those over D or O rings and webbing, i will keep using the latter,as being more cost effective.

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## Re: Broadseaming theory

Originally Posted by Todd Bradshaw
Remember, I don't build, and have never built Tyvek sails, so my impressions of its stretch and stability are just based on handling samples of it. Whether or not I would modify a sail's shape to allow for excess stretch would have to be based on real life examples. For unusually stretchy cloth, I would still probably change the broadseaming rate as a first attempt rather than trying to guess how much to shift the draft.
I see. Well, my sail is intended for extremely light winds, so if using 1/2'' per 2.5' results in too much camber, it won't hurt too much. I'll report how it performs for any future Tyvek sail builders.

From what I can tell the biggest variable in the halyard angle is probably the amount of mast that sticks up above the mast/yard intersection. The less excess mast you have above the yard, the less that angle can vary. One thing about lugs is that once you hoist one, it becomes pretty obvious that you are hoisting a contraption up a mast with few attachment points compared to other sail types. It's kind of like flying a kite from a stick. There are various methods with parrels, different ways to rig the halyard and even hardware that can be added to the mix to help fix it in position if needed - but even so, I think it's wise to expect to need to do some experimentation with the halyard's position on the yard once you actually start your sea trials. The figures and formulas that we use for drawing sailplans and fitting them on hull drawings using centers of effort, centers of lateral plane, lead etc. are just design guidelines. Much of the time that you are actually sailing the boat, they either won't apply or will be inaccurate. They do help us get the design figured out, so that we have something to build to, but the final word is always testing and adjusting out on the water. Even America's Cup syndicates with nearly unlimited funds and massive computer design and performance power at their disposal can't always tell what will work best until they get out on the water to test and tweak it. As nice as it might be to be able to figure out all these factors on the drawing board before building the boat, it seldom works that way in real life, and it is certainly possible to "over-think" some of this stuff ahead of time and drive yourself crazy.
That's what I had in mind too - have the yard raised up as high as possible to leave less to chance. I always wondered why so many lugs leave so much of halyard from the mast head to the yard. Maybe it makes sense in certain arrangements, but I'm glad to hear from you that it is not necessary. I even decided to use dumb sheave instead of halyard block at the mast top, so that I can raise yard even higher - both for the previous reason, and also to have as much sail area as possible (it is kind of limited by mast length - I must keep it no longer than 4m, because that's the length of my car on which I'll transport the boat). Dumb sheave also makes sense for lug sail, I guess, because it will tend to jam, which is good when I'll tension the downhaul after raising the sail - if halyard jams, only a fraction of it's length will be a subject to stretch. And after releasing downhaul, it will unjam for easy dousing of the sail. Or so I hope.

My wife is a molecular biologist from Latvia.

Contender Sailcloth is made in Europe and they have outlets in The Netherlands, France, Italy, Germany, Spain, The UK and Sweden. They make an all purpose 4 oz. cloth for small boats and their premium "Supercruise" also in 4 oz. weight. Both are also available in 5.4 oz. for slightly bigger sails.

Dimension Polyant Sailcloth is another good one. They are headquartered in Germany with outlets in France, The UK, Italy and Russia. They build a full line of woven fabrics and also some very neat Mylar laminates.

Challenge Sailcloth and Bainbridge International (both American-based) also have outlets in Europe.

Most of these companies deal wholesale, rather than retail (at least they do over here). Rather than trying to set up a wholesale account to build a couple of sails, the best bet may be checking with sailmakers reasonably close to you to see if they will add a few yards of cloth for you to one of their orders. Adding a retail mark-up, handing a small roll of cloth over the counter and collecting a check is pretty easy money for most sailmakers.
Thank you! I knew there must be something. I went through their websites.

There is one thing that puzzles and irritates me about these high-end companies. They make such an effort to show off in the best possible way. Perfect website design, lots of information, thorough product information. Almost everything you need to know. And yet, somehow they manage to "forget" to include price catalog of their products. I mean, come on, how hard is it? In my country, it is a standard practice that every company which sells something and has a website, lists prices of each product, as well as shipping (even if they don't have an option to buy from the website), so that customers can see, compare, plan ahead. But with these high-end companies, it seems almost if their customers are millionaires who don't care the slightest about the prices.

Or maybe, these prices are so steep that they would drive customers away, so they say "contact us for pricing information" so that they can have a chance at sweet talk and persuading.

Seriously, why do they omit such a simple and important thing?

Originally Posted by keyhavenpotterer
There is a UK seller of Dacron sailcloth. He lists his materials on eBay. Good man.

http://www.ebay.co.uk/sch/m.html?_od...cloth&_sacat=0

He stocks end of roll, or rolls with faults in them somewhere. These rolls are of no use whatsoever to the sailmakers but are perfect for guys like us who make a single sail or just a couple of sails. Couple of years ago I built a sail the same size as yours for about £40. He did prefer you call in to see him but hopefully since you are a long way away he will ship to you.
Thanks! At least this guy tells his prices. Well, shipping costs as much as the fabric itself... But I'll keep this in mind.

Originally Posted by keyhavenpotterer
Brilliant source of sailcloth. You need double sided basting tape. You also need the proper star grommets. Try to buy these from a friendly local sailmaker. They are usually helpful and slightly amused that you are trying to make a sail. Hardest thing to get hold of was the punch to close the grommets. Again local sailmaker lent me their old set for the afternoon. You can buy the tools but you need three for the different sizes and that will be too expensive just for the odd sail.
Originally Posted by skaraborgcraft
I have gone to using D rings and webbing for attatchments rather than grommets, mainly for the reason Brian mentioned that a set of different size punches and setting tools is a big investment for someone making a one-off sail. I have had a friendly sailmaker set some corner eyes in a hydraulic press, but given the cost of those over D or O rings and webbing, i will keep using the latter,as being more cost effective.
Well... About the "local friendly sailmaker". I just happen to have one in my town, and he is probably the only sailmaker in our country that knows what he's doing. He has a reputation of being extremely angry (my guess is knee pain), but despite that, 4 years ago, I decided to pay him a visit. Wanted to ask some advice, see his stuff, get some guidance, as I wanted to learn a bit about sailmaking. This guy just bawled out on me, went totally berserk. He said that unless I own a proper yacht and have a few thousand bucks in my pocket, I shouldn't ever dare to disturb him anymore. He said he loathes us amateur sailors, and the only place we have out on the water is in the bottom of the sea.
I was discouraged at sailmaking for a long time after this, but here I'm trying to get back at it again.
What I mean is that the only way to obtain rare sailmaking items is searching myself... This guy won't help.

Well, thank you everybody, especially you Todd, it was extremely helpful. I would never have figured all that by myself. I already recommended this thread for 3 of my friends, as a wealth of useful info accumulated here. I have no more questions, and will now continue working on my boat project. It is entering the final stages, and soon I'll begin producing plans. After that is done, I'll post it here in this forum, and I dare to hope that some of you will have time to look through it and criticize my design so I can modify it before I start building (due in June).

But of course, we can continue our discussion here, if anybody wishes to add a comment
Last edited by Laukejas; 02-09-2015 at 10:31 AM.

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## Re: Broadseaming theory

I realise you asked about broad seaming, but if you would also like to learn about sail shaping using a computer sail design program which is free and has taught me loads about sail shaping and is fun to play with. The software is free and designed to create final panel shapes which it outputs as XY plotted shapes. The SailCut4 version is for four sided lug sails.
http://www.sailcut.com

Brian

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## Re: Broadseaming theory

Thank you, Brian, I am well aware of this program. I even programmed my sail into it, and then printed provided panels on paper (small scale), and sticked it together to see how it shapes up. Here's how it looks:

Pic1
Pic2

The problem with this program is that it is intended to be used with laser plotter or cutter. It would be a painstaking and possibly inaccurate undertaking to plot these panels on cloth by hand. I thought about printing them on paper and then tracing onto cloth, but there are just too many steps, each possibly adding inaccuracies.

If only this program could provide traditional broadseam amounts as well as edge curves, I'd gladly use it, but since I have no laser cutter, I don't see how.

Anyway, this program is somewhat limited. It shapes the panels, yes, but it doesn't take a lot of variables into account.

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## Re: Broadseaming theory

Wayne Gabrow was kind enough to share his article from 1983 about his theory on broadseams. I do not understand it yet, but maybe some of you will find it useful. He posted it on his blog:

http://developable-surface-boat-desi...il-design.html

Seems very promising.

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## Re: Broadseaming theory

Originally Posted by Laukejas
Thank you, Brian, I am well aware of this program. I even programmed my sail into it, and then printed provided panels on paper (small scale), and sticked it together to see how it shapes up. Here's how it looks:

Pic1
Pic2

The problem with this program is that it is intended to be used with laser plotter or cutter. It would be a painstaking and possibly inaccurate undertaking to plot these panels on cloth by hand. I thought about printing them on paper and then tracing onto cloth, but there are just too many steps, each possibly adding inaccuracies.

If only this program could provide traditional broadseam amounts as well as edge curves, I'd gladly use it, but since I have no laser cutter, I don't see how.

Anyway, this program is somewhat limited. It shapes the panels, yes, but it doesn't take a lot of variables into account.
I found the XY plots very easy to use. Simply use the long edge of the roll as the Y axis and plotted using a square to measure the X distances. I also did a model size drawing, making the paper the same scale size as my printed scale panels so I could work out the panel layout on the cloth. This all worked fine. Sewing the sail was the work. Developed great admiration for sailmaker that day.

Brian

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## Re: Broadseaming theory

With time on my hands, my cloth being on back order, I mocked up both my sails full size out of kraft paper and 1/2" wide double stick office tape. The broad seaming was quick and easy and the whole project only took a couple hours for both sails on my 130 sqft cat ketch sprit rig. It gave an accurate preview of the final draft/ shape and where the seams will end up. The paper is even stiffer than the cloth, so while assembling all kinds of nuances become very clear. When the cloth arrived, I proceeded to cut much more confidently. Also, I have them folded up, dated, and stored away for future reference if needed.

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## Re: Broadseaming theory

Originally Posted by keyhavenpotterer
I found the XY plots very easy to use. Simply use the long edge of the roll as the Y axis and plotted using a square to measure the X distances. I also did a model size drawing, making the paper the same scale size as my printed scale panels so I could work out the panel layout on the cloth. This all worked fine. Sewing the sail was the work. Developed great admiration for sailmaker that day.

Brian
Well, maybe so. It's just that this method allows no secondary cutting, as in traditional sailmaking. This means these edges have to be sewn together flawlessly, with each end coincident down to millimeters. If I were to do it, I'd probably pin the ends, then the middle, then 1/4ths, and so on, until I'm dead sure that panels are aligned correctly. It might be very tricky to find these points on curved edges, though. How did you do this step?

Originally Posted by chrisring
With time on my hands, my cloth being on back order, I mocked up both my sails full size out of kraft paper and 1/2" wide double stick office tape. The broad seaming was quick and easy and the whole project only took a couple hours for both sails on my 130 sqft cat ketch sprit rig. It gave an accurate preview of the final draft/ shape and where the seams will end up. The paper is even stiffer than the cloth, so while assembling all kinds of nuances become very clear. When the cloth arrived, I proceeded to cut much more confidently. Also, I have them folded up, dated, and stored away for future reference if needed.
I plan to do the same when I finish my boat plans. What scale did you use? I was advised to go for 1/4, but that is pretty large for a model, I'd say.

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## Re: Broadseaming theory

Considering that Tyvek is not a woven material, would it not respond differently? In my experience making sails and sail repairs with it, although minor at best, I would say that it does not stretch at all like a woven material.

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## Re: Broadseaming theory

I plan to do the same when I finish my boat plans. What scale did you use? I was advised to go for 1/4, but that is pretty large for a model, I'd say.[/QUOTE]
I built the paper sails full size using the same floor space and layout I used again later when the cloth arrived.

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72

## Re: Broadseaming theory

Originally Posted by Michael D. Storey
Considering that Tyvek is not a woven material, would it not respond differently? In my experience making sails and sail repairs with it, although minor at best, I would say that it does not stretch at all like a woven material.
I think it behaves similarly. Tyvek has a bias stretch, meaning that it stretches more diagonally than it does horizontally or vertically.

Originally Posted by chrisring
I built the paper sails full size using the same floor space and layout I used again later when the cloth arrived.
Well, since Tyvek is nearly as cheap as paper, I don't think I'd gain much from full-size mock up...

29. ## Re: Broadseaming theory

I'm muddling my way through sail design. After finding the possible CLR of the boat using a cardboard cutout of the underwater profile of the boat balanced on a pin, then the CE of the sails ended up with something along these lines:

I scrounged some old sails from a forty foot cruising ketch that was about to be scrapped and cut my test sails out of the middle of the old ones. Then hemmed the edges, pounded in a few grommets, and tried em out. The test sails performed surprisingly well, and gave an idea of whether I'd come close to balancing the rig to the hull. They also showed a few places where I'd like to make some modifications.

Though the sails may have had some belly from years of use, I was relying completely on edge round against the mast and gaff to shape them. No broadseams were built in. Now I'm looking at building a new suit WITH broadseams and after some varied advice, I've come up with a plan for the sails.

And offered up for critique is my latst plan: I'm particularly interested in input on the size of the broadseams.

30. ## Re: Broadseaming theory

I'm particularly interested in input on the size of the broadseams.
Your broadseams are pretty strange. On vertically cut 4-sided sails the broadseams are done in specific zones, as shown earlier in the thread. They would never taper out equal distances from an edge. For most of these (gaff, lug and spritsails) the broadseam zones would be something similar to the areas shown in purple here on that drawing. Your gaff sails will also have luff round added, which this lug does not, but the broadseaming is basically the same process.

Broadseams exist on any seams that pass through those zones, with their "zero points" at the inner borders of the zones. Their lengths would be the lengths from those points to the sail's edges, and all different. The rate of broadseam overlap increase varies a bit with the amount of bias stability of the fabric you are using. Most recreational fabric is in the medium stability range and a typical overlap rate would be about 1/2" increase per 30" of broadseam length on 36" wide cloth panels. For narrower cloth panels, the overlap increase rate would be reduced proportionally because more seams would be present (example: 18" wide panels = a rate of 1/4" overlap increase per 30" of broadseam length). Harder finished, stiffer cloth would be broadseamed more and softer, less stable cloth somewhat less.

The increase should be a smooth even taper until you get within a few inches of the edge. At that point, you increase the rate slightly, which builds just a small amount of cup-shape into the sail's edge (but not too much). I don't know if anybody has published a suggested amount for this final flare at the end of the broadseam. It is one of those things you learn by doing, I guess.

On a vertically-cut gaff sail, you can't really broadseam the luff (not enough seams striking it to work with) so your draft is going to be a combined product of how much luff round you add and how you broadseam the top and bottom of the sail. In traditional sailmaking, we can help make draft by adding luff round as a small percentage of the sail's horizontal chord width, measured and figured at several spots along the luff. Typical for cruising boats would be about 2.7% (2.7" of luff round added for every 100" of chord width). You plot several levels up and down the luff, measure the chords, add 2.7% of those distances, ahead of the luff, and make a mark for each. Then you get out a batten and fair those marks into a clean curve with the original throat and tack corners at top and bottom (nothing added at those spots). The 2.7% figure will generate a sail with about 1' of draft per 10' of chord width, which is considered "normal". A fat heavy boat that needs more power to push it through the water might benefit from more draft, so we might use a 5.4% ratio, which produces 1' of draft for every 7' of chord. A lean, fast, easily accelerated boat wouldn't need all that pushing power and could benefit from slightly flatter (and faster) sails. Using a 1.2% factor for that boat would yield 1' of draft for every 15' of chord width. With just those three percentages, 2.7%, 5.4% and 1.2% you could probably outfit 90% of the recreational boats out there and have pretty decent performance.

You do want to stick pretty closely with your hull type though. Sticking a shallow draft, fast sail on a slow hull will usually lack power and make an even slower hull, and a deep draft sail on a fast hull will tend to be inefficient, slow and hard to control.

Once we have added our round to produce the desired draft, we need to position that draft. We don't want our draft all piled up against the back of the mast - we want it toward the middle of the sail. Traditionally, this is mostly eyeballed, but we know that the area between the inner points on the broadseam zones for a vertically cut sail will be the area where its draft will be deepest. The safest bet for most boats is to stick these "zone peaks" about 45% of the way aft of the luff edge. For a really fast boat, we might go as far forward as 35%, but again, what is good for one, isn't necessarily good for the other. 35% on the wrong hull will probably actually make it slower.

How far "inland" the peaks are from the sail's top and bottom edges is up to you. I'm sure computers have formulas for this, but I don't see in 3-D. I walk around on the lofting sticking bits of tape down as markers and looking for a couple spots that seem "right" to me (big help I know, but I've been shaping sails by eye for a long time - and sometimes I probably still get it "righter" than other times). I like to visualize a smooth curve from mid bottom, up through the deepest draft peaks and wind up at the head, usually 40%-45% aft of the throat corner. The bottom zone's peak will be maybe 40%-45% up from the foot (in traditional sailmaking 45% is a magic figure for distances and usually works for placing anything you aren't sure of - max luff round, foot round, leech hollow, head round, etc.). I don't usually make the head broadseam zone too deep (tall). The throat area won't tolerate a whole lot of draft, so we want some draft and broadseaming up there to keep the sail from being too flat up high, but we don't want to go nuts with it. On a high aspect 4-sided sail, like an unusually tall gaffer or lug we probably don't need the bottom purple zone to be 40%-45% tall at its peak. We can then lengthen the space between the zone peaks and give our sail a longer mid-height airfoil section.

31. ## Re: Broadseaming theory

Whoa. This is immensely helpful. A few basics that I was not understanding. Thanks!

32. ## Re: Broadseaming theory

What I'm not quite smoking is how 2.7% of 10" can equal 1"
What am I doing wrong? (120 x 0.027 = 3.24)

"The 2.7% figure will generate a sail with about 1' of draft per 10' of chord width, which is considered "normal"."

33. ## Re: Broadseaming theory

2.7% of 10" doesn't have to equal 1", but adding 2.7% of ten inches as luff round and attaching it to a straight mast will create 1" of draft in your chord. I really have no clue how the math works out on it, but I've been using these luff round formulas ever since I learned them from Jim Grant (Sailrite's founder) about 1980, and they seem to work, as far as I can tell. The quoted figures were as follows, with the percentage of chord width added as round, out ahead of the straight luff reference line between the tack and throat (4-sided sail) or tack and peak (3-sided sail) corners, followed by one foot of draft being generated for a given chord width:

.7% - 1' draft in 20' of chord (a very flat sail for a very fast, easily accelerated boat, like an iceboat)
1.2% - 1' in 15' (common on quick, light boats like beach cats or fast planning dinghies)
1.6% - 1' in 13' (a bit more power added, cruising multihulls and quick monohulls come to mind)
2.7% - 1' in 10' (considered "normal" for most cruisers and recreational boats)
5.4% - 1' in 7' (deep draft for a fat, heavy boat that needs lots of power to push the hull through a chop)

These figures will then be combined with the placement of our broadseam zones, which in turn will position the maximum chord depth somewhere along our sail's horizontal chords. A figure of about 45% of chord width aft of the luff reference line is a pretty good bet for most boats. Something faster, like a beach cat or fast racing monohull can often benefit from moving the maximum draft forward a bit more (maybe something as far forward as 35% aft of the luff reference line). Naturally, and as always, we also may need to consider spar bend, as it has a way of eating up our edge curves before they can do anything, so in some cases we are adding as much or more round to our sail's edges to compensate for bend as we added for draft, if those edges are to be attached to a spar.

34. ## Re: Broadseaming theory

I've made something like two dozen sails exclusively following the Emiliano Marino book. They have all come out just fine. It really is all in there, just work through the chapter(s) on making a plan (can't remember the chapter name). Use the sample plans that he gives to help answer any uncertainties that you might have.

It's not rocket science.

35. ## Re: Broadseaming theory

I am aware that while 'rocket science' and sail design have some overlapping principles, sailmaking may not be quite as complicated. But it does seem fairly nuanced. I'll get to the bottom of it, though more likely somewhere in the middle.

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