Thread: Broadseaming theory

1. Re: Broadseaming theory

I've always considered truly good sailmaking to be more a matter of how many small design and detailing factors you can juggle in your brain at once, as they can all make subtle (or sometimes not so subtle) and visible differences in the quality of the finished product. The devil's in the details and not accounting for a few of them, not considering them important enough to bother with, or even being able to see they're missing on the finished product is usually what separates many amateur-built sails from really good ones.

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Side by Side, Sail Rig Test

Please pardon my entry into this subject thread that I found when I was searching for more info on 'broadseaming'. I found Todd's contributions very interesting and informative, particularly this quote...

Originally Posted by Todd Bradshaw
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.
Brief summary. I am looking to perform a side-by-side outdoor model test of two sailing rigs,...
1) a std fractional rigged sloop rig
2) my unusual 'single-masted ketch' rig (with a mast titled forward)

I'm thinking approx 6 foot tall rigs,...just the rigs set upon a flat plate representing the deck of a large cruising multihull. Both rigs would have identical sail areas.
https://www.boatdesign.net/threads/s...utdoors.52977/

Over the years I have had many naysayers, and some true believers. I have defended the concept in a long drawn out forum subject thread, and many references to the aerodynamics of the situations. I want to perform this relatively simply outdoor test to just show that my aft-mast rig will NOT suffer from windward ability to the degree that some naysayers claim, and may even outpoint the traditional rig if I simply add a fairing to portions of the 'bare mast'
https://www.boatdesign.net/threads/aftmast-rigs.623/

My dilemma,...do I try to build true broadseamed sails for these 2 models, or utilize more simply flat panel sails?? I am concerned that some of those naysayers may claim my results invalid it I use flat-panel sails.

Like Todd said above, "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."., I tend to agree with him particularly when considering the overlap of headsail and mainsail...
Last edited by brian eiland; 08-08-2017 at 10:08 AM.

3. Re: Broadseaming theory

Brian-
You'll be thought of more highly, and get better responses, if you put your case into its own thread. Though the unconventionality of the rig might not find its best audience here.

Cheers, Dan

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Re: Broadseaming theory

Originally Posted by snaildrake
Brian-
You'll be thought of more highly, and get better responses, if you put your case into its own thread. Though the unconventionality of the rig might not find its best audience here.

Cheers, Dan
I thought about that, but it was Todd Bradshaw's response I was specially looking for,....not so much on the viability of the rig idea, but rather on whether to utilize model sails made with the extra effort of broadseaming.

5. Re: Broadseaming theory

It is a good thread to bring back anyway.

6. Re: Broadseaming theory

I am concerned that some of those naysayers may claim my results invalid it I use flat-panel sails.
I would most likely be one of them. The question isn't really about broadseaming, it's about whether or not the sails are flat or have camber. Broadseaming is basically just a sewing technique which allows flat panels to be shaped into a specific, non-flat shape. If your cloth panels have straight, parallel edges, you would need to broadseam them to build shape into the sail. It helps to distribute extra cloth from luff round away from the mast and into the rest of the sail. If you were to build the sails as radials, similar to what is shown in your drawing, then the panel edges would be cut in curves (generally dictated by a computer program) and then joined with constant-width seams. Two different ways to essentially generate the same sail shape.

I don't think you can run a fair test that means much with flat sail models of sails which in reality would never be cut flat when made full-sized. It is also pretty difficult to make a model sail which is accurately shaped because the broadseams (or panel shaping on a radial) are in some places very small on real sails and difficult at best to duplicate in a scale model. When combined with fabric characteristics, seam widths, stitch sizing and other elements which often can't be accurately scaled down, making a model and then claiming the real sail will perform the same is pretty risky. You might generate some interesting results with the tests, but I doubt you will change any minds or truly solidify and justify your theory with them. The way you get someone's attention in a sailboat is to sail higher than they can and faster than they can with a real boat.

....and depending on how sleek that multihull is, you can probably move your draft forward to the 35%-40% range, with a fairly round entry to prevent stalling. A flatter entry can be faster, but a more rounded entry will usually work more consistently, as fast boats move through changes in wind speed and direction, and more rounded entry angles handle it better.

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Re: Broadseaming theory

So putting some accurate draft (as well as can be done in that scale size) would appear to be the way to go,...that is what I was thinking also.

Perhaps i can do the broadseaming with just good glues (no stitching), as these test sails only have to last few a days at moderate winds (not-heavy).

8. Re: Broadseaming theory

Originally Posted by Todd Bradshaw
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.
Correct me if I'm wrong but isn't the logic behind these figures that you lay a stiff string along the chord, lift the middle 1", and measure how much longer the string is?

/Mats

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Re: Broadseaming theory

You are still trying to make a 3D shape out of a singular flat panel of material. Yes, you can manipulate the edge cuts and attachment of such edges in such a manner that it appears to have 'shape', but its still not an accurate representation of a real sail that has been either broadseamed of more modern built by laminated over a 3d heated mold.

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Sail Shape, via broadseaming or what?

Sail Shape, via broadseaming or what?

Originally Posted by brian eiland, post: 790384, member: 399
...
The sails remain in question. There are a number of materials from which they might be made. But I have a few questions to ask of the naysayers as to the shape and sophistication of these sails to satisfy their 'demands' for accuracy.
1) Being that these are such a relatively short rigs (~6 foot), I do not see any necessity for modeling any twist in the sail shapes?

2) How much effort should there be to panel these sails to produce what optimum draft in the sails?

3) Perhaps it might be easier, and as accurate, to produce these model sails over a 'form' much as they do with the big boys in 3Di?
http://www.northonedesign.com/Technology/3DiExplained/tabid/20214/language/en-US/Default.aspx
.....ideas, suggestions....??
I'm up in the UNESCO port town of Lunenburg Nova Scotia on holiday from the FL heat, and I got to rethinking about the making of the sails for my model test. I ran across this discussion topic on another forum...
Broadseaming Theory

We realize that before this modern day of 3D lamination and load path making, etc that most real boatsails developed their shape in 2 manners,...shape built into the sails themselves and constraining the edges/corners of these sails. I'm concerned

primarily here with how the shape is built into the sails,...know for years as broadseaming. I've searched around quite a bit and I do NOT detect the utilization of 'broadseaming' in model boat sailmaking. What I do find is a lot of cutting along the edges of singular pieces of flat panel material to affect the shape of the sails when rigged to straight edge restraints. looks nice, but of questionable accuracy to get good drafts and twist etc in model sails.

Why be so concerned? If I really want to convince some of the naysayers about my aft-mast rig, I think I need to make the most convincing model of real sails for the two 6' tall side-by-side model rigs as I can,...And that means the most accurate draft-twist model sails I can build (hopefully without excessive expense).

I had been thinking I might be able to bend a large rectangular sheet metal piece int a nice smooth arch with something like a 50% draft shape, then lay out a piece of my model sail material (unknown exactly which material at this time), over this 'sheet metal mold' ,...and on a skew cut out my triangular model sails with varying drafts and twist from top to bottom.
But I had run across this website reference that sort of put a wrinkle in that plan...
http://www.onemetre.net/Build/Sailmake/Sailmake.htm

From my understanding of sail making, there are two ideas I want to contradict.

The first idea is that you can make sails by accurately cutting a curve on a panel, and then attaching it (stitching, gluing) to another panel. Well, while you might be able to cut a good curve some of the time, your fingers just don't have laser accuracy in them to stick A to B and you'll hardly ever obtain reproducible or reliable results. (It might be possible to butt-join the curved edge to another curved edge with a little more reliability, but this doesn't yield what the Equipment Rules of Sailing define to be a seam. Such a sail couldn't be used in sanctioned IOM competition, though it would be OK in a development class.)

The second idea is that you can drape your panels over a "camber board" and get a nice shape that way. Well, let me be clear about what I'm knocking here. I take a "camber board" to be a length of curved surface, where the curve is like the surface of a cylinder. In this case, your panelled sail will have exactly the same shape as a single un-panelled sail and, if you wanted a three-dimensional shape, you've wasted your time (though the result certainly looks the part).

Larry's booklet is the only source I know which carefully explains the use and construction of a sail block. I am sure that this is really the only way (in your garage, please, not in some specialist workshop!) to make professional sails, to obtain reliable and reproducible three-dimensional shaping, and to be able to tweak and change your shaping as you learn about the whole business.

Sail Blocks Analysis www.onemetre.net/Build/Sailblok/Sailblok.htm

Any other ideas as to a relatively simple way to build accurate sails for these 6 foot tall models??

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Sheet Plastic Sails

BTW these sails I made for the display model were made by stretching plastic sheet material over a metal sheet mold, then heating it to set to a curved shape,....looks good, but not accurate.

https://www.boatdesign.net/threads/a...-46#post733497

12. Re: Sail Shape, via broadseaming or what?

Originally Posted by Todd Bradshaw
It is also pretty difficult to make a model sail which is accurately shaped because the broadseams (or panel shaping on a radial) are in some places very small on real sails and difficult at best to duplicate in a scale model. When combined with fabric characteristics, seam widths, stitch sizing and other elements which often can't be accurately scaled down, making a model and then claiming the real sail will perform the same is pretty risky.
^This, in BIG capital letters.
Originally Posted by brian eiland
Sail Shape, via broadseaming or what?

I'm up in the UNESCO port town of Lunenburg Nova Scotia on holiday from the FL heat, and I got to rethinking about the making of the sails for my model test. I ran across this discussion topic on another forum...
Broadseaming Theory

We realize that before this modern day of 3D lamination and load path making, etc that most real boatsails developed their shape in 2 manners,...shape built into the sails themselves and constraining the edges/corners of these sails. I'm concerned

primarily here with how the shape is built into the sails,...know for years as broadseaming. I've searched around quite a bit and I do NOT detect the utilization of 'broadseaming' in model boat sailmaking. What I do find is a lot of cutting along the edges of singular pieces of flat panel material to affect the shape of the sails when rigged to straight edge restraints. looks nice, but of questionable accuracy to get good drafts and twist etc in model sails.

Why be so concerned? If I really want to convince some of the naysayers about my aft-mast rig, I think I need to make the most convincing model of real sails for the two 6' tall side-by-side model rigs as I can,...And that means the most accurate draft-twist model sails I can build (hopefully without excessive expense).

I had been thinking I might be able to bend a large rectangular sheet metal piece int a nice smooth arch with something like a 50% draft shape, then lay out a piece of my model sail material (unknown exactly which material at this time), over this 'sheet metal mold' ,...and on a skew cut out my triangular model sails with varying drafts and twist from top to bottom.
But I had run across this website reference that sort of put a wrinkle in that plan...
http://www.onemetre.net/Build/Sailmake/Sailmake.htm

Sail Blocks Analysis www.onemetre.net/Build/Sailblok/Sailblok.htm

Any other ideas as to a relatively simple way to build accurate sails for these 6 foot tall models??
If you really want to model a specific sail shape, make a male mould of the shape that you want and hot form a membrane over it. Dunnop what flexible plastic sheet will hot mould over a former, but that would remove the issues with the inaccuracies inherent in building a model sail from flat panels.
Flexibility would not be an issue if you only sail on one tack for your trials.

On the other hand there is software that will design your sail.

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Re: Broadseaming theory

Is it easy to translate broadseaming into curves?
Just cut a curve the width of the broadseaming on one side of the panel?

Found that image of the Spindrift 11 sail on Sailrite.

Are all BS noted over 6" when they are described in the plan like on this in the foot?
Does that mean that all other seams are debited for the same distance?

Like the first seam that says 41"> BS. 3/4". The seam widens from the sleeve/luff to the leech 3/4" every 6" until 41".
What happens after the 41"? A streight line to the leech or a gentler curve until the panel has the same width like at the luff?

Sorry for the confused writing.

14. Re: Broadseaming theory

My guess is that the distance of the seam from the | mark to the luff is 41", the broad seam starts att the | mark at 0 and tapers towards the luff ending up being 3/4".

/Mats

15. Re: Broadseaming theory

^ No, I think that the seam widens to an additional 3/4 inch over 41 inches. What you suggest is a seam that finishes about 5 inches wider at the tack.

Cross post with Mats

16. Re: Broadseaming theory

A standard panel seam on a small boat sail is a 1/2"-5/8" overlap. The broadseams on that sail would start at the small vertical marks, working toward the luff edge, and the seam overlaps would begin to widen until it reached the luff - where your seam would be as wide as the original 1/2"-5/8", plus the additional fraction dictated for broadseaming (like 3/4" or whatever). That fraction is a product of the length of the broadseam and one of several formulas. Depending on the cloth firmness, your rate of broadseam width will change. Stiff, stable cloth needs more (wider) broadseaming than softer, more stretchy fabric. So you will have a formula that may say something like "for medium cloth, widen your seam 1/2" for every 28" of the broadseam area's length". That's where those fractions came from.

They don't show you the broadseaming curve on the drawing, which determines where each broadseam starts on the panel seams. This would be a curve beginning at the luff, maybe 2/3 of the way up and ending at the foot around 45% of the way aft. There is no exact formula for these, it is up to the sailmaker's eye. They also don't tell you that the broadseams should flare a bit (a short increase in overlap rate right near the luff edge). The amount of this flare (or not) will determine the sails' luff entry angle (more flair = rounder entry and a more forgiving sail to trim. Less flair = a flatter entry, more speed on a fast hull with less brute power for punching a heavy boat through chop and less forgiving of steering/trimming errors).

The tack broadseam (if present like above) is usually broadseamed at twice the normal rate - so if we're broadseaming for cloth calling for 1/2" per every 28" of broadseam length, this seam would be broadseamed at a rate of 1" per 28". In addition, there would normally be a couple of very small broadseams (straight with no flair, maybe 1/8" overlap increase and 18"-24" long) on a couple of the panel seams along the leech. These help keep the leech tight and not flapping as the cloth ages and softens up a bit.

As if this all wasn't complex enough..... The formulas were generally written back in the days when all sailcloth was the same width, which for Dacron was 36" or so. These days, you can save money by buying Dacron made 54" wide, or if you want the old school look, you can make sails by cutting the cloth down into narrow panels. More or less seams will dictate that you will need to change your broadseam rates or frequency if you want to accurately build the same the sail shape that's on the plan. This little lateen was a Dacron replica of a cotton sail from about 1910 and was built with 9" wide panels. By combining some rather narrow broadseams with some panel seams which were not broadseamed at all, the total amount of broadseaming and the sail's shape were about the same as a sail made from four or five hunks of 36" wide cloth would have.

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Re: Broadseaming theory

Do I understand that right?

The curve in the panel got the highest point at 41" from the sleeve edge. Does it curve back or does it go a streight line to the leech?
Can I divide the curve between the lower and the upper panel or do I draw the curve on one and sew together with the other (streight) panel?

How do you make a curved sleeve or do you see a streight one and then attach it in the curve to the sail?

The foot seam. It is just a wedge over the whole seam?
It would end in about a depth of 3/4", the same as the 41" seam?

I'll try a 1:5 paper model first.

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Re: Broadseaming theory

Thank you Todd.

You are a goldmine of knowledge. I am still trying to process this whole thread, not that easy for me being a non English speaking, metric person.
I am going to try drawing up the curves, offset them so that I can tape together my panels at a constant seam width.

19. Re: Broadseaming theory

The seam is straight (say 1" wide) from the leech to the mark, then it widens in a fair curve to 1 3/4" at the luff, with an exception to the fairness in that it widens a bit more right next to the luff.

/Mats

20. Re: Broadseaming theory

In reality, you don't mind with battens and such for broadseams, just make a straight line from where the broadseam starts to where it ends. I used "fairness" above without thinking

/Mats

21. Re: Broadseaming theory

As for the "foot seam", it's called a dart, I believe, I don't know how to interpret the drawing but 3/4" seems reasonable but I'd be tempted to devide that 3/4" into two or three darts

/Mats

22. Re: Broadseaming theory

Real sails don't have darts! Sails made by people unskilled at sailmaking (or trying to be extra cheap) have darts. A foot broadseam (relatively vertical and helping to create a bit of a cupped shape and add some end plate effect to the foot) should start at the lowest panel seam and run all the way down to the foot edge - and on some sails, there may be more than one of them. At first look, it may look like the sailmaker ran out of cloth and had to piece the bottom panel. This is not the case. They are important shaping seams. Darts create pointy hard spots at their beginnings in anything other than really soft cloth, and are generally a sign of poor workmanship. If your sail has a vertical broadseam on the foot, it will most likely be around 45% aft, at the point of deepest draft.

Can I divide the curve between the lower and the upper panel or do I draw the curve on one and sew together with the other (straight) panel?
In some cases, the mating of a curved panel to a straight panel is common. Picture a typical cross-cut Bermuda sail which will have a foot rope which slides into a tunnel on the boom or attaches with slugs/slides. One of the most confusing things when I was first learning sailmaking were the instructions for making such a foot. They had you panel the sail all the way down to the tack seam and then stop. You then would lay the next panel over the lofting and along the tack seam area from the upper panel, with a foot curve down below, and then cut it to shape, with the foot curve. Then you flipped it over, upside down, and basted and sewed the foot curve to the straight edge of the panel above it. Once done, it created the lower sail draft near the foot and a straight edge that would fit along the top of the boom. Totally confusing to read about, but once it was actually tried, it all became clear. In typical, cross-cut and vertical cut sailmaking that's usually the only time you would join a curved edge to a straight one, and foot shaping is usually done just with vertical broadseams, but it could also be done for sails with loose feet, sprit-booms, etc. - where you end up with one bottom panel with no vertical broadseams, but still having some shape.

In radial-cut sailmaking, you are frequently joining curves together, though they usually are mirror images. If you take the concept to extremes, you can even come up with a shape like this balloon. All seams are mirror images being joined, but an individual small panel's curves at its top and bottom may be different curves, thus yielding the teardrop shape. A horizontally cut spinnaker would be cut similarly to one vertical section of this balloon, with mirrored curves being joined - more curvy up top for a rounded shape, and less curvy down below.

Run-out: Generally when designing a horizontal chord or foot shape for a sail, the aft part of that curve is kept pretty straight. Too much curve back near the leech usually doesn't work very well.

23. Re: Broadseaming theory

Ok, thanks, so not a dart, my mistake.
Is it normal with just one foot broadseam?
Come to think of it, are there cases when you'd make luff broadseams on a sail with vertical panels?

/Mats

24. Re: Broadseaming theory

Vertically cut sails like lugs and sprits have broadseams on their heads and feet. A vertically cut 3-sided sail, like a Leg-O-Mutton would have foot broadseams and might have a bit of broadseaming on any seams which terminate on the luff, though depending in the sail's perimeter shape, there may not be many (if any) opportunities, as there may not be seams striking the luff edge.

25. Re: Broadseaming theory

Right, yes, I was thinking of if there are vertically cut sails with broadseams made at a 90 degree angle from the last seam to the luff. Similar to the foot broadseam above, but for a vertically cut sail.

/Mats

26. Re: Broadseaming theory

I haven't seen any, though it might be a way to adjust luff entry angles, similar to the way foot broadseams can cup the foot area a bit.

27. Re: Broadseaming theory

I have learned enough of sailmaking to understand a bit of how little I know...
I thought that the use of horizontally cut sails became popular because it was more efficient to put the broadseams on seams hitting the luff than on the ones hitting the foot...

/Mats

28. Re: Broadseaming theory

The reason cross-cut sails became popular was because they were faster. The old natural fiber sailcloth had so much stretch that the panel-to-panel seams (which were four layers thick) tended to make ridges because the seams stretched less than the panels around them. Cross-cutting aligned the ridges with the airflow over the sail, rather than impeding it and causing turbulence as vertical ridges would do on vertical cuts. With modern synthetic sailcloth this really isn't much of a factor these days on anything other than light nylon spinnakers, drifters, etc. Those light sails can now be made using simple overlap seams and special stretchy seam tape without stitching on most of the seams. The result is a very smooth shape - usually using radial cuts, but you could do them almost any way and still get a smooth shape.

29. Re: Broadseaming theory

Originally Posted by mohsart
Right, yes, I was thinking of if there are vertically cut sails with broadseams made at a 90 degree angle from the last seam to the luff. Similar to the foot broadseam above, but for a vertically cut sail.

/Mats
Everything that I have seen on building vertical cut sails puts the broad seaming on the head only.

30. Re: Broadseaming theory

The broadseaming area is actually larger on the foot of a vertically cut sail than it is at the head. A fair bit of this is due to the fact that the throat area of a four-sided sail can't tolerate an awful lot of shape and still set well, but since the top third or so of the sail tends to be narrower, and the head shorter than the foot there just isn't a need for a great deal of draft up there. Foot broadseams will be longer (the broadseam area beginning in the same general place as the sail's maximum draft) and being longer, they will end up being bigger (wider - more panel overlap) as well.

31. Re: Broadseaming theory

I was thinking of big cotton lugsails built at the end of the 19th C with loose foot and wire luff rope used by sailing herring drifters. It is on record that the Scottish sail makers could get a roach to stand on the leach of a vertical cut lug.
With the canvas and hemp rope stretching at different rates, building them would be a whole different ball game.

32. Re: Broadseaming theory

Most of the original, old cotton small boat sails that I have had come in for replication (usually in Dacron, but not always) had no broadseaming at all and simply relied on cloth stretch and a little bit of luff and foot round for shape. Since you can't stop bias stretch on natural fiber sails, even if you want to, they worked OK that way. Some of the really old sails from the canoe companies were pretty obviously not built by sailmakers. Trim-out and other things just weren't done the way sailmakers of any era would have done them. It makes you wonder whether the canoe company folks just went down the street and made a deal with a tailor to make them a few sails. They were usually totally flat, with no shaping seams, spar bend allowances, or edge rounding at all. Since they were used on tender, easily-driven boats which were often overpowered in terms of sail size, they got away with it and the sails did the job.

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Re: Broadseaming theory

Can I ask your opinion on my sail design here?
I am building a copy of the PT 11 dinghy (in 4 segments) and really have no clue about sails other than what I am reading in the internet.
I have got a 465cm epoxy windsurf mast for now.
I might get a professional made sail when the hull turns out good (all joints are watertight, doesn't break and float ok) but for now I like the challenge of seeing it myself and learning what can be done.

I am relying on sailcut now. Can do 1:1 templates in cardboard for the panels. Maybe the oscillating knife can also cut the Tyvek I am using if it is secured on/between cardboard.

So here is what I've come up with in sailcut.

Also how do you do the edges? Just sew them over once?
Do you see in the mast sleeve when the sail is done? Is the sleeve curved like the luff and made out of short segments?

Thank you,
Marcus

34. Re: Broadseaming theory

First a warning: Sailboard masts nearly always make terrible masts for other boats. They are too whippy. On a real sailboard situation, they are pre-bent into a rather stiff curve by the boom and outhaul and basically stay that way for the duration. This is not the case when made into a dinghy mast. It is extremely difficult to make a sail that sets and works decently for a mast that has so much uncontrolled flex. Sails have to take mast flex into account when they are designed, and allowances for it are built into the sail's design. There is so much flex in the typical windsurfer mast that it is impossible to allow for it. The end result is that your sail's shape and draft placement are all over the board as you are trying to sail the boat. You could make a better mast by laminating a few 1 x 4s together and cutting them to shape.

I have never used, or messed with Sailcut, so I don't know what factors they account for (or don't) so I can't really give you a valid opinion on their design. It is done by panel-shaping, rather than using constant-width panels and broadseaming as would be done in traditional sailmaking. Panel-shaping is fine and the way we make modern radial-cut sails with computer programs, though this is a pretty simple sail to make the traditional way from a few constant-width slabs of your material. Edges would be either hemmed (leech and sometimes the foot) or bound and reinforced on nearly all sails. If there is a sleeve for the mast, it is usually made from a long, constant-width strip of cloth which is "bent" where needed to follow the luff shape. Class racing sails, for boats with sleeves and bendy masts (like those for a Laser) usually start out this way (pretty basic) and then will eventually evolve over the years to a final design as the result of a lot of small adjustments to the design.

Using traditional sailmaking techniques instead of a computer, a sail like your boat needs would be built this way, which may help you understand some of the basic principles involved:

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

It's written for polytarp sails, but doing one in Tyvek would be pretty much the same deal.

35. Re: Broadseaming theory

Originally Posted by Todd Bradshaw
Most of the original, old cotton small boat sails that I have had come in for replication (usually in Dacron, but not always) had no broadseaming at all and simply relied on cloth stretch and a little bit of luff and foot round for shape. Since you can't stop bias stretch on natural fiber sails, even if you want to, they worked OK that way. Some of the really old sails from the canoe companies were pretty obviously not built by sailmakers. Trim-out and other things just weren't done the way sailmakers of any era would have done them. It makes you wonder whether the canoe company folks just went down the street and made a deal with a tailor to make them a few sails. They were usually totally flat, with no shaping seams, spar bend allowances, or edge rounding at all. Since they were used on tender, easily-driven boats which were often overpowered in terms of sail size, they got away with it and the sails did the job.
This thread piques my curiosity, so I just dug out the original cotton sails built for Peerie Maa back in the early '50s. Sewn out of the finest cotton with hemp roping. The gunter main is vertical cut with a laced foot. The seams are 4/8" wide sewn with straight stitching. There is broad seaming along the foot, increasing the seam width by 1/8", and only in the last three seams at the peak/head, again increasing the 4/8 by 1/8 to 5/8".

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