Alternative to marvelous Buccaneer 24

Well Doug, I've never had to take a chainsaw to any boats I've built, maybe the hand/eye/brain is not so bad after all. This is an area where you thrive too. Here are a few measurements: 7.62 LOA x 7.9m BOA, main hull WLB 0.350m, Block coefficient 0.32, Prismatic coefficient 0.44, Vert. prismatic coefficient 0.54, foil measurements 185 x 1500mm OA, 400mm bury, rudder 185mm x 1200mm, IT area 185mm x 1m approx, SA upwind approx - 33sq.m, displacement approx 200kgs, Bruce No. upwind 2.5, rig height 11m, wing mast chord 1m (perhaps), SA downwind 50m2, Bruce No 3. But all these figure will probably change when Sid is completed ... so it was hardly worth posting them. Jpegs of main hull and early stages of the lower J sections of the float foils.

 

A Cp of 0.44 doesn't sound right for this type of craft. Have you made an error in a calculation?

 

0.4390 according to Freeship - maybe it's computing the spread wing overall mainhull beam. True hull beam, if the gunwale was not spread, is just under 500mm.

 

Here's the difference:

 

Yes, redrew Sid (or close to Sid) without spread wing deck - here:
Block coefficient 0.3406
Prismatic coefficient 0.4945
Vert, coefficient 0.5172

 

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Thank you.

Prismatic still seems low-do you think its ok?
How about projected SA/WS?
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Interesting on Cp: http://www.wingo.com/proa/prismatic/index.html

Might help to review Cp and Cma here-even Doctors review textbooks(Chapter 3, page 9) :

 

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Gary, that would seem to give a really low immersed aspect ratio-2.16 . Most lifting foils on , Moths,the Rave, Mirabaud etc are on the order of 7/1 minimum. What's your thinking on this?

 

Not sure why you are using the gunwhale at all. Cp is calculated with immersed dimensions.

Most monohull keelboats will fall between 0.52 and 0.56. I believe modern multihulls are all 0.58 or greater.

 

Well that's what the printout reads - and I've always wondered why the figure was so low. But who cares, I like the look of Sid's hull as it is ... and it will go through the water okay plus carry the rig and 2 crew. The foils to me Doug, seem pretty large - and I hope to reduce them after testing. Mirabaud looks way over foiled to me and way too complex; be a pig in the light. Check out the size of G. Marx's from my earlier posts, a 650 kg boat and they do a great job of keeping the lee float and boat up - and they have been cut down from the original size because they gave too much lift. Can't remember the measurements, will do so later. They are not large. Maybe what I see isn't really happening. But no, crew with me have noticed the same thing. Strange eh? I have a saying - there are NO rules, what counts is that it works.

 

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I wasn't talking about the size of the foil-I was refering to the aspect ratio of the foil......

 

I tend to agree with you, Gary. The rules serve as the base point, getting one in the ball game, setting parameters for what is going on. The real deal happens out on the water and sometimes, I have been surprised by the way things have unfolded, as opposed to what the rules said would happen.

Can't tell you how many times I had to pick up stuff that broke in stressed conditions and paddle back to shore. Fun and nicely humbling experiences. I'm sure that there will be more along the way.

 

Ah sorry. But they ARE skinny, high aspect ratio foils Doug, in fact I'm going to find it difficult enough as it is at 185 x 1500mm to get enough strength into them to carry the platform loads at speed and not distort or break, hence I might be shortening them. I'm talking white cedar strip core and laminates of carbon, not full carbon layup; this is a backyard build after all, in the B24 tradition, as per original philosophy. Anyway you're getting too far ahead, I still haven't skinned the main hull. There will be plenty of changes.

 

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My figure AR=2.16 was based on what you said the "bury" was-maybe I misunderstood. The overall AR is a bit over 8/1-but isn't part of that in the boat?

 

Bury to me means canterlevering bury; what's in the case and float, not the immersed foil in water.

 

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On that basis, my figure of 2.16 was correct. I'm not saying it's bad, necessarily-just in comparison with other foilers I know of its low. I don't know the aspect ratio of the Hobie Trifoiler "J" foils-maybe I can find out.
I would like to feel more comfortable using a low aspect foil in some applications so I'm going to check into this more....

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Hobie Trifoiler "J" foil: