Building a Full-Foiling Fiberglass Beach Catamaran

This thread is really a continuation on the "Just an Idea!" thread over in Sailboats. My friend found a buyer for his Nacra 5.8 hull, and so we are unable to use that hull for a foiling trimaran, so I've decided to continue the project, but now with a foiling Catamaran. I've always liked cats more than tris, anyway. (Mainly just looks.) However, I've never built a fiberglass boat or mold or plug, and I do not know the process, but I am willing to learn. Here is my design. The boat will have a Wave-Piercing bow design, and I am planning to construct hulls that are much like the one used on the White Dragon foiling catamaran. The rig I will be using will either be a small A-class rig, or a Nacra 5.2 rig. The crew weight will be around 160 pounds sailing double-up, and around 80-90 pounds single-handed. (I will change the rigs accordingly. I want a single trapeze on both sides of the boat. I want the boat to foil in 6-8 knots of wind, and travel 25 knots downwind, and 13 knots upwind. The foil setup will be an uptip foil on each hull, and two T-Wing rudders. Thanks in advance!

Also: One of the parts I'm most worried about is constructing the rigging. Vang, cunningham, sheets. They look hard to build and rig.

 

In planning to build a foiling beach cat, the rigging is the least of your worries. For starters - you probably won't even have a vang! I would strongly recommend investing plenty of time in research and gaining real practical experience in all the relevant facets of this project before you start mixing up any pots of resin or cutting any cloth. It could save you hours of wasted effort in the longer run.

 

Thank you for the advice, Munter. Do you know of any good sources for the information, or any links to beach cats other people have built? Thanks.

 

Stealth-home built foiling cat: New Catamaran Foilers https://www.boatdesign.net/threads/new-catamaran-foilers.51898/ post #6

 

Has anyone built a fiberglass one? And what do you think of my design? Thanks.

 

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I saw the parameters you want to include in your design-haven't seen a completed design? You should order the Vellinga book in case you don't already have it.
You say you want uptip foils but the characteristics of those foils on a cat means that you will have to retract and deploy a foil with every single tack or gybe. Have you considered wand controlled foils like the Whisper, S9, Vampire and I Fly? Have you been able to sail as crew on a foiler? The more research you do the better your final boat will turn out.
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Depending on the conditions where you will sail , you might want to consider targeting a lower windspeed takeoff like the Whisper:
Whisper http://www.whiteformula.com/WhiteFormula_UK/Whisper.html
The Whisper is a one design class, but when it comes to the styling, the sky is the limit. Our customers have had some pretty wacky ideas, so we are looking forward to a pretty interesting start line, coupled with the ability to foil in just 4 knots of wind we could see some “pretty fly styles”.

 

Most foilers are carbon, or make extensive use of it so they are light but strong. It will give you some construction tolerance, whereas you'll need a lot of skill to make a boat out of fibreglass and keep it to a reasonable weight for a foiler.

The crew weight of 80–90lbs (36–40kg) is very light, someone that size struggles to manage a Moth (35kg all up), a 6m foiling catamaran will be more than a handful. Your design sounds a lot like a Nacra 17, I suggest you check out the Z board version to see what you think, maybe go for a sail. It will give you some idea of the scale of the endeavour you're about to embark on. Optimum weight for Nacra 17 crew is 135kg all up (65–70kg each).

 

Also have a look at the papers on Ceres and Calliope by the Chapmans on the AYRS website - Catalysts https://www.ayrs.org/catalysts/ - in Issues Nos 2 and 10. Not new they may be, but they are successful amateur designed and built foiling cats.
Having looked at those, browse later issues for more ideas; Vampire for instance in Nos 50 & 51.

 

Here is an idea I had, please check my sanity; what about a miniaturized version of an AC50? It's got a proven foil system that shouldn't be too difficult to adapt to a smaller boat, I can try to build a wingsail, if I can't I'll just strap a soft sail to it. Thanks.

 

AC 50's use foils that require constant adjustment while sailing. Very complex systems. There are numerous small cats using auto-stable versions of uptip foils that don't require constant adjustment--but they do require raising a lowering the foils every tack or gybe.
There are "Z" foils used on A Class cats and some others that allow the foils to be left down. Other types of surface piecing foils(as opposed to fully submerged foils) can be left down as well but when used on a narrow platform have reduced righting moment.
I still think there is a lot of potential with a properly design foiler trimaran............

 

What about a mini AC-50 with some Uptip or Z-type foils on the hulls? I'll try a trimaran after this, Doug.

 

WK, there are numerous small cats using UptiP foils and a few using "Z" foils. About the only thing they have in common with the AC 50's is that they are catamarans.
There are no production small cats that I am aware of using wing rigs but if you did a LOT of study you could build one though I wouldn't recommend it.
Steve Clark is a member here-you could send him an e-mail/PM and he might answer you.
Have you considered building or buying something like a UFO?

Steve and Dave Clarks UFO https://www.boatdesign.net/threads/steve-and-dave-clarks-ufo.56326/

 

I was talking about using AC50 hull design adn crossbeams, rig and foils later.

 

Because of the size of the AC 50 it would be almost impossible to literally scale down the hull design. It would probably be better to copy a hull design very close to your chosen length. An AC scaled down to 18' including crew would be about 297lb-subtracting 160 from that leaves a maximum boat weight of 137lb. An 18' A Class cat weighs around 150lb. So using your weights for two the scaled down hull would not work, using your weight for one(about 80lb) the platform would work but it is unlikely that 80lb would create enough righting moment.
You could see if you can find someone with an A that might let you sail it or at least tell you if 80lb is enough weight for the boat. An "A" is as close to a scaled down AC 50 as you're likely to find. Sailed with two(at your weights in post 1) and an extra trapeze might just work except it wouldn't be legal in the A class.

 

Please show how you arrived at that number. An AC 50 is about 2,332–2,432 kg (5,141–5,362 lb) just for the hull. Adding foils and rig will considerably increase the weight. I realise it's not a simple matter of scaling at 18:50, but I'd like to see the factors you're using.

I think the OP's requirement for a 45kg crew to single–hand a 6m foiling catamaran is unrealistic in anything more than about 10kn of breeze, maybe less (so likely only foiling downwind). For that size crew, I'd keep the length to no more than 4m, maybe somewhere around UFO size (a tad over 3m) which seems to be more than enough for 80kg crew to foil and have fun.