I'm really interested in sail design and construction. I've got the sailrite books/pamphlets and a couple of books like the "Sailmaker's Apprentice", but I've found very, very little on the art and science of high performance sail construction/design for our catamarans. North Sails put out a book, but the reviews indicated it's more of an advertisement for North. That's not surprising since they're in the business of building and selling you their sails...

Any ideas on good literature for sail design, specifically aimed at our "high speed" sails?

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Chuck C
NACRA 500 Mk2
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Not a book recommendation but try to avoid this sail shape



Edited by MN3 on Oct 27, 2021 - 03:20 PM.

I don't understand. Why???

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Chuck C
NACRA 500 Mk2
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I've decided the easiest way is going to be if somebody on the forum figures it out and shares it with the rest of us!

MN3's sail seems to be performing.

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Bryan in Poplar Grove, IL
Supercat 17, unknown year. Future project
Hobie 16, 1977 - died a spectacular death https://youtu.be/Y7O22bp2MVA
Hobie 16, 1978 - current boat
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Well, of course it is - you can tell he bought one of the new-fangled deck-sweeper sails. Looking closely, I REALLY can't tell what the issue he has with it is, though... Maybe there's too much twist...

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Chuck C
NACRA 500 Mk2
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charlescarlis

I don't understand. Why???

too much material in the luff
if you are not careful the excess sail will tickle your armpit as you hang on to the mast

the results could be catastrophic and a catastrophe

I think you're going to have a hard time finding a book on the subject b/c that's the "thing" that high performance sail lofts sell. They aren't just selling you a sail, they're selling you their design.

For example, you can buy an F-18 main from a large number of lofts and it will be easy to see that some sails are faster than others. The fast sails have a better shape and it came from years of testing and experimenting, not a book.

To get a start, my opinion would be to read books about aerodynamics, sailing theory and sail shape. The books that I've read and like the best were written by C. A. Marchaj. Specific to catamarans, they literature is even more limited, however....

Once you have a foundation in the theory, then try your hand with some free sail design software like Sailcut CAD. Problem is, you're going to run into a wall pretty quickly because....

The next step is what the better lofts are selling with their design; the use of FEA and CFD analysis to evaluate the shape of the sail. The big lofts use their own proprietary software, which you'll never get access to. If you're capable enough, you could try using OpenFOAM, or if your budget is big enough buy something like SMAR Azure. Go do some reading about the software suite that North developed, it's pretty impressive!

Many of the lofts that we use for beach cats have designs that are improved iteratively over years of development. Starting from scratch is tough and I prefer to give guidance to the loft for what I want and let them do the hard work.

Thanks-pretty much confirms where I'm at. Found a few good research papers on line, but not so interested in fluid dynamics at this point. I am pretty good at aerodynamics of solid wings and have some awesome resources to lean on, but that is nowhere near the same as sails. This is a foray into better understanding and experimenting-not a change of career, nor trying to cheap out on sails.

It seems the state is just as you described-you can get information on building and classic construction techniques, but once you start getting closer to "high performance" and recent design improvements, available info. gets rare because of competition. And, that's fair. I think at this point, it's time to start playing around and experimenting.

Here's my payout- understanding the forces and effects along with sail design will help me bend my sails to their best performance. And, then perhaps how to modify sail controls from stock to assist. For example, I never knew why Aussies seemed to love over-rotating masts, besides it being a speed improvement. Then, learning that a flat sail with a well rounded leading edge/luff reduces stall tendency, which trends around changes of apparent wind speed made sense. Makes the sail more forgiving as well as bringing the camber forward improving speed potential.

I THINK I got that right, but please forgive me (and by all means correct me) if I didn't-still learning.

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Chuck C
NACRA 500 Mk2
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charlescarlis

I'm really interested in sail design and construction. I've got the sailrite books/pamphlets and a couple of books like the "Sailmaker's Apprentice", but I've found very, very little on the art and science of high performance sail construction/design for our catamarans. North Sails put out a book, but the reviews indicated it's more of an advertisement for North. That's not surprising since they're in the business of building and selling you their sails...

Any ideas on good literature for sail design, specifically aimed at our "high speed" sails?

Best thing is to start working at a loft. Like everything, you will need to work your way up. When you mention "our catamarans", which cats are you referring to? Keep in mind, we have everything from a Hobie 16 to Nacra 5.0 to Prindle 19 to Tornado to Flying Phantoms and A-Cats. Everything non-foiling is pretty simple, keep draft at approximately 22%. The deeper you go, the more power you have. For my modified P 18-2, we went with a flatter design because I sail mainly high winds and singlehanded or with kids. So far, it has worked pretty well in all conditions. The biggest factor to consider is a high or low aspect ratio rig. I have a pdf article on aerodynamics that does a pretty good explanation. But, it really depends on where you are sailing, wind conditions and your style of sailing. There are some sail lofts I cannot make go at all, and others I am golden.

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Scott

Prindle Fleet 2
TCDYC

Prindle 18-2 Mod "FrankenKitty"
Tornado Classic "Fast Furniture"
Prindle 19 "Mr. Wiggly"
Nacra 5.8 "De ja vu"
Nacra 5.0
Nacra 5.8
Tornadoes (Reg White)
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"Looking for book / reading on high erformance sails Bottom"

try searching high Performance sail making?

also go to sail lofts, talk to pros, find out what they recommend, maybe "pretend" to be a buyer (and actually buy) but let them cut it and you sew it?

i learned a lot a a Doyle sail shop. they made me 3 mains and i learned a ton
also i purchased a few jibs from Whirwhind and he was great to talk with

MAKE SURE you talk with sailmakers that sail and better if catsailors!

In 2015 I was approached by a customer about making a deck sweeping A-cat sail. This was prior to one available in the US. I did not have any experience designing sails but I did have an aviation background and gave it a shot.

I used sail-cut for the first sail. Due to an error in understanding the program I wound up with a perfectly flat sail. It was quite crude, it went on to win 7 of 10 races it was entered in. That might have been one of the most successful sails ever built! Sailcut is a very crude program but it will work to get you started. IMO, if it would allow a draft station at 5% and 95% it would be 100x better, maybe someone out there could change that.

After that I invested in SMAR AZURE and started making improvements. Smar allows many many more customizations to the sail. I worked with Smar to make the program capable of an upside down portion for the deck sweeper. I made 12-15 sails with 4 distinct generations between them.

If you understand an airplane wing, you understand the sail. You're trying to generate an area of low pressure as efficiently as possible. Think of the mast as the slat and leech curve as the flap.

The mast is an integral part of the sail design. Spend ample time studying the mast and what it does with certain inputs. Then consider the effect this puts into the sail.

Chord in the sail makes it easier to keep the air attached, but it also adds drag.
Draft in the sail adds power or "grunt" but also adds drag.
Leech curve adds power but also drag.

Getting feedback on your design is tough. Most sailors do not know why a sail is good or bad.

Building laminate sails is a lot of work and expensive. My sails were successful in performance but not in build quality. I wasted a lot of money on products that did not perform as advertised and lead to failures. Unfortunately a sail fails at a regatta. If your lucky it ruins just one race but that's rare.

It costs about $800 IIRC on materials to build a Technora A-cat sail. You will also need about $7k worth of tooling.

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Greenville SC

Offering sails and other go fast parts for A-class catamarans
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Here are the pros building sails.

https://www.northsails.co…manufacturing-minden-usa

Thanks, Bacho- that's really the kind of experience report that adds a lot. While I know that working ag a loft, etc. is "the right" way to learn to build sails, I'm not interested in starting a struggling business. I'm interested in doing better and understanding my hobby. A bit like hot rodding a car or bike. I appreciate the perspective. How did you go from sailcut to cut material? Did you manually plot or what?

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Chuck C
NACRA 500 Mk2
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A friend has a big vinyl printer/plotter. We put the sail material in there and printed it.

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Greenville SC

Offering sails and other go fast parts for A-class catamarans
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Well, dang! That went through my mind as I have access to vinyl plotters and would simplify the issue MASSIVELY to use a vinyl plotter. Much less real estate. And while it sort of precludes actually cutting it, that can be done by hand relatively easily, since this is playing and one or two-off stuff.

So, I'm guessing the sail material has permanent marks (registration marks, seam offsets, etc.)? And, what kind of pen did you use?

Any problems encountered when feeding the dacron through instead of vinyl? I'm guessing that, due to the length of material involved, you have to watch it pretty darned closely.

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Chuck C
NACRA 500 Mk2
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Well I over simplified it a little.

The first sail we printed. It took 10 hours IIRC. The ink on the mylar is not durable and needed to be treated with care. We did have issues with the material wanting to work its way to one side or the other.

For later sails we used a marker in the blade holder and marked them that way. It was much faster, maybe an hour per sail tops. By then we treated them as multiple shorter panels to mark instead of one long one.

The issue with the marker was it created a thick line over the uneven surface. The shaping in the sails was very slight, the marker lines left a lot of room open for error.

If I did it again I would prototpye with Dacron.

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Greenville SC

Offering sails and other go fast parts for A-class catamarans
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No, I get it, there's a ton that goes into plotting large format anything correctly. Interesting about the pen issue. I've seen where a loft was using a pen plotter, a fine line sharpie and was plotting on laminate that looked "bumpy". I'm guessing a spring-loaded pen going across the surface would provide for a more accurate shape.

What maximum dimension panels did you end up marking the gores onto?

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Chuck C
NACRA 500 Mk2
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