# Thread: Broadseaming theory

1. Senior Member
Join Date
Apr 2012
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441

## Re: Broadseaming theory

Thank you Todd,
A great instruction.

I will make a wooden mast. Is there any easy way to make a parted wooden mast? That was the idea in using the sailboard mast in the first place.
What would be the dimensions of a wooden mast about 470cm long?

For the sail I will go with the preshaped panels, broadseaming still feels a little intimidating.

Marcus

2. ## Re: Broadseaming theory

I usually suggest Iain Oughtred's spar specifications to my customers. That would put the mast at 1:52 in diameter of the length (measured from the partners or deck to the masthead). Below the partners it can taper to about 2/3 of that. Above the partners it retains about 90% of the full diameter at half height and then can taper to as little as 50% of full diameter at the masthead for that type of sail. So your full diameter would be around 90mm, half height about 81mm, 60mm at the heel and as little as 45mm at the masthead. I might go a bit fatter at the top for stiffness. Making sails which work well on bendy masts is much more difficult than those for a stiffer mast.

3. Senior Member
Join Date
Apr 2012
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441

## Re: Broadseaming theory

What would be the luff round for such a mast?
Mine is 90mm at 50% now.

4. ## Re: Broadseaming theory

Usually about 2%-2.5% of chord width, plus a bit as a bend allowance, depending on how flexible the mast turns out to be. There is no real formula for bend allowance. It is up to the sailmaker's experience.

5. Senior Member
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441

## Re: Broadseaming theory

So if the chord at 50% luff is 1440mm the curve would be 4cm + something....say 5-6cm? My 90mm are probably too much?

Very confusing this is

I guess I would have to know how much my mast bends first?

6. ## Re: Broadseaming theory

It's not unusual to be building-in more curve for bend than for draft, but yes, it is nice to have at least a good hint of how much the mast will bend. There have actually been a couple instances over the years where I had customers lay the mast with boom attached on a roll of paper, tie the peak to the clew of the boom, tension it with simulated leech and mainsheet tension and trace the curve of the bent mast. These were mostly gunters though, where two spars of different diameters are partially overlapped, not both plumb, and they're held together with a rope. Good gunter sails can be very tricky to design.

You can weight spars (usually by bridging them horizontally between the peak and partners areas on a mast, or both ends of booms or yards) and hanging a weight in the middle. Stretching a straight string above them allows you to measure the amount of weighted deflection at various points. Typically for small boats, the weight used is equal in pounds to about 1/3 of the sail's area in square feet. It's better than nothing, but it's little more than a rough estimate. You also don't always build in an allowance as big as the bend measurement. In some cases (like Sunfish-style or canoe lateen sails) those long skinny yards and booms bend like crazy. If you build in all the possible luff or foot round for bend allowance, the sail will be way too drafty and deep in light air when less bend is happening and performance will be poor. You have to arrive at some sort of compromise, usually based on previous experience. A Sunfish yard or boom will bend about 8". You usually build in about 3" of allowance for decent all-round performance - which will probably work better in some conditions than others, but it's the best you can do and is aimed at nice, medium sailing days.

Yep, it gets confusing. Sailmaking has three distinct phases to learn. First is the design phase. Once it's lofted out, that part is pretty much done. Then there is the sewing part, and learning to do it cleanly because every stitch shows. Finally, there is the reinforcement and trim-out. Each phase will have challenges, and probably a few judgment calls. One reason I usually suggest that folks start with a pre-designed kit from a place like Sailrite is that most of the tough brain work is already done for you and you can begin sailmaking by concentrating on the assembly part. Which is plenty for now. I suppose that a free on-line sail design program can cut you a decent sail - if you know what to tell it, so that all the factors that need to be taken into account are there. There-in lies the rub for most beginning sailmakers.

7. Senior Member
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441

## Re: Broadseaming theory

Thank you,I measured the mast bent with 9kg and it is around 4cm.I'll just go with my 55mm luff curve. We'll see...Tyvek is cheap and I got enough for another sail.Another question that might sound stupid.Do you first sew on the smaller corner batches and then go bigger and bigger or do you start with the biggest?How long is the biggest corner relative to the edge and how many batches do you see on?I read all that somewhere...either in the instructions you sent or here.Can't find it anymore though.

8. ## Re: Broadseaming theory

Smaller first. I learned after I finished my sails that the sides of the largest patch should be 10% of the sides of the sail.

/Mats

9. ## Re: Broadseaming theory

Tradition generally seems to be the second largest patch first, followed by the next smallest and the next smallest after that if there is one, and finally the biggest patch of all on top of all the rest. Then you sew through all of them. It helps to draw light pencil lines on the biggest patch that show the sizes of all the patches under it as sewing guides, because you often can't see them when sewing. Four layers of patching is usually enough on Dacron sails, though if it's a really narrow corner I may use more to get a bit more beef in that area. Shape is up to the builder, and around 10% of that edges overall length is good for synthetics. Cotton sails can have fewer and smaller patches due to the more stretchy nature of the natural fabrics. They tend to have less concentrated stress right at the stitch lines holding the patches on. For Tyvek you would want to be patching similarly to the way it is done on Dacron.

10. Senior Member
Join Date
Apr 2012
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441

## Re: Broadseaming theory

Perfect.
Your sails are a delight to behold. Just beautiful.
I just went ahead, cut and taped the sail that afternoon/evening.

Had it hanging too but need to edit out my wife first

11. ## Re: Broadseaming theory

Todd,

What's the reason for the concave curve of the foot?

/Mats

12. ## Re: Broadseaming theory

Originally Posted by mohsart
Todd,

What's the reason for the concave curve of the foot?

/Mats
Because artists always paint sails like that?

I'll get my coat.

13. ## Re: Broadseaming theory

That sail was built for a gentleman who was restoring an old Duckboat and wanted a period-correct looking sail rig for it. We hunted through old books and found mostly photos of spritsails on them, as well as a couple of lugs and even a small gaff sail. Many had that strange (but kind of cool looking) elongated clew corner with a hollowed foot - hollowed mostly to prevent flapping, I assume. It could certainly also have been built with some broadseamed foot round and would have been fine, but we decided to stick close to the old examples we found. This is the building plan I came up with for him. It does not show the broadseaming along the head and foot edges as I broadseam on the floor by eye as I baste the panels together. Having made a whole bunch of small, vertically-cut, four-sided sails over the last 35 years or so, I can pretty much broadseam in my sleep. The "owner's manual" that I sent out with the finished sail is the PDF below. Unfortunately, I never got a photo of the finished boat.

http://webpages.charter.net/tbradsha...lans/!DUCK.PDF
Last edited by Todd Bradshaw; 08-16-2017 at 04:03 PM.

14. FF
Senior Member
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Oct 2005
Location
The Netherlands
Posts
371

## Re: Broadseaming theory

I used Sailcut 4 for the first lugsails I did. I used it to make templates for the panels since I had to make at least a dozen than. I used a T square and a measuring tape that I had glued at the edge of my table and it worked well. Robert Laine who developed the program did it the same way at home. That particular program worked only for crosscut sails but I think now you can use also versions for vertical cut sails. Since than I work with a sailmaker who has a plotter/cutter but when I was asked th do a square sail for a Viking Ship Replica he could not help me for he did not have software for such a sail. He said I could cut it in a way most sailmakers here (The Netherlands ) used before they were converted to computercut sails. If someone is interested I could describe the proces but I need to do some drawings to make it clear and don't know how to post them. I might do in my Blog however, that I can do.

15. Senior Member
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## Re: Broadseaming theory

I think I messed up the sleeve.
It's too big.

How do you really make the curve? I glued the parts 2 cm under the luff curve and folded them around to see them together following the curve again.
How I got a little twist in the middle of the sleeve.
Should I open the seam again and try to make the sleeve smaller? The mast is also tapered, should the sleeve get smaller to the top?

How can I repair that?

16. ## Re: Broadseaming theory

Is there really a problem with a (too) big sleeve? It seems to me to be (if anything) a good thing, reducing turbulence...

/Mats

17. Senior Member
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Apr 2012
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## Re: Broadseaming theory

I might try it. Have to do the boom first anyways. The geommets are still missing and I don't know if the curve is any good.

18. ## Re: Broadseaming theory

A wide sleeve is fine, and as mentioned it may reduce some turbulence. The thing that is critical is keeping the designed luff edge of the sail the same distance from the back of the mast (unless it has been designed differently and with the sleeve width in mind). If the sail was laced to the mast, or had slugs or slides in a track the object would be equal spacing between the luff and the mast all along the luff edge. The sleeve system is supposed to operate pretty much the same. If the mast tapers, the sleeve (or its overlap depth onto the sail's edge) will need to be altered to account for it. Otherwise, the spots where the mast tapers without the sleeve tapering will basically work like adding more luff curve, beyond the designed and desired amount of sail draft. Getting sleeves to work properly can be pretty tricky, especially on a flexible mast.

19. Senior Member
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Apr 2012
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441

## Re: Broadseaming theory

Thanks, more luff curve would be fine anyways. Mine seems to be pretty tame to the original PT-11 sail.
I was worried about the head grommet and the halyard but then I realized that these kind of sails don't need one when you close the sleeve at the head.
I am now looking into the rigging (saw all that before but gave it to little thought beforehand). The gooseneck on the PT-11 somehow snaps to the mast. On the Truc 12 they use some fixings over the gooseneck and some fixing ring for the vang
https://www.h2o-sensations.com/11095...-with-boom.jpg
Does the boom even need something to keep it on the mast or is the vang alone enough?

I am really curious if my "sail" will somehow look like a real sail on the water

20. ## Re: Broadseaming theory

If the mainsheet and vang are pushing the boom jaws against the mast that will usually be enough to do the job - possibly with a ring or "bump" added around the lower mast to limit just how low the boom can drop. One of my iceboats essentially just had a fork on the boom's end and a small and simple tack downhaul with a sleeved luff. There was a "cross" at the open top of the sleeve, made from two short hunks of seat belt-style webbing, sewn on 90 degrees to each other to keep the masthead from poking up and out of the sleeve's top. The boom on that one was also sleeved, with a couple reinforced openings where the mainsheet blocks hung. It all worked very well.

21. Senior Member
Join Date
Apr 2012
Posts
441

## Re: Broadseaming theory

What would be the best way to cut my sail down.
I want a higher boom and maybe a boom that angles upward aft.

I will probably do a new sail and keep the first one (might try battens on that).
Should I rather try a sail like that on the Reverso or keep the triangle?
https://static1.squarespace.com/stat...e?format=1000w
Any ideas what I could do?Screenshot_20170917-224052.jpgScreenshot_20170917-224146.jpg

22. ## Re: Broadseaming theory

What choises do you have? Cut out a bit of the foot.
Then you have to make a way to reinforce the foot, clew and tack with ropeing and patches.

Battens seems like a good idea where the sail has a convex leach.

I don't see why keeping the Marconi/Bermuda sail would be of any disadvantage, given that it is relatively balanced as it is now.

Rising the clew may be accomlished by raking the mast forwards, that may or may not be a good idea depending on other factors.

/Mats

23. ## Re: Broadseaming theory

You may also want to resew the sews in the lower part of the sail if you cut off parts of the foot, making new broadseams corresponding to the new sail shape.

/Mats

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