Post your design ideas

Plywood racer/cruiser second iteration. The main hull is smaller and has been simplified. More volume in the amas.

 

Dont know the exact weight yet. I need to work out the internal structure of the main hull, but I think I can get it under 1200lbs bare weight.

 

which software was used to desig it?

 

freeship version 2.89

 

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Raps, why the flat side of the ama to the inside?

 

As the ama gets pressed, the surface presented to the water becomes flatter... and hopefully generates lift. Borosan made a good argument for this... also there is a nice discussion about this ama shape in a W17 trimaran design article, and there is a 35' planing trimaran posted somewhere on this forum with a similar ama shape. I will most likely change the pitch and perhaps the size of the surface. I was going to play with the shape in michilet. The other option is using s shape like the buc 24, but that is an extra chine... I tried to minimize the the chines here, which is why the deck house looks the way it does. Chines can take the place of a stringer, but they are heavier than a stringer.

 

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Well, you know most asymetrical cat hulls like the Hobie 14 and 16 were designed with the flat side outboard. The flat side is the high pressure side and the inside is the low pressure side if your trying to develop lateral resistance. Personally, I feel you'd be better using a low wetted surface high L/B ratio ama and develop "lift" with a nice high aspect board.....
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Sun Night 4/10/11 : are you thinking those shapes would enhance vertical lift-not lateral resistance?

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This is a Dick Newick design with asymmetrical amas-flat outside-curved inside: http://councill.home.mindspring.com/sbjournal/tri/tri6.html


Pictures showing asymmetrical hull with flat side outboard; "Hobie-like" hull-Hobies had the flat side outboard.....

 

While those floats are certainly assymetric, the Argonauta floats aren't flat on the outside, they have a concave surface that is designed to generate dynamic lift. New Moon amas were also at one time optional on the tremolino and used on some of Newicks larger designs - there are a few older Echo's etc here that have them. His newer designs have a more conventional symmetric high bouyancy ama.

Check http://www.tremolinotri.com/amatest.htm

 

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Thanks for the info-they looked as flat as a Hobie 16 hull in the only views I could see. Like you said-the point is their asymmetry compared to the apparent "flat on the inside" asymmetry Raps is proposing to use.

Jamez, this sketch is what the Argonauta ama looks like to me based on the pictures on the site-is it even close?

(click on image)

 

The photos certainly don't show it very well. There is a cross section in this old design article. Also a pic of an Echo with that style float.

 

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Thanks -it sure looks like two different amas between the one I posted(mindspring) and the one you just posted. I think I get the idea ,though.

 

I was going more for the float shape of the w17 and the 35' plywood planing tri I saw on this forum..... but I can't seem to find it now. I'm going for fast and lo tech. I'm trying to prove a point here, which is you don't need to spend six figures on a boat to get speed and have fun. Look at the success of the i550. And people are spending 10,000 getting one of those boats on the water! I want to get a faster, boat, less buildtime, home brewed rig (and home made or used sails)
More performance, for less money, for more people.
If the boat works well (and I hope it will) I'll post the plans here for free like alik did with some of his wood boat designs.

My point is, lets put things back into perspective. The f25c is a sexy boat, but even used it is 2.5x more than the median household income in my county. I don't believe sailing as a sport should be only for the rich. The lightning class is strong where I live, and a competitive boat for that fleet is about 5000. And that is how I arrived at my upper price limit. I could "afford" a new f22, meaning I could make the monthly payments, but I would rather keep That money and invest it, and retire early, and sail a wharram cat around the world before my hair turns grey than work until I'm 67 and own a f22...
so please, any ideas that would help get the most performance out of a low tech build, lets hear them!

 

The one thing that I tried that seems to Make a rather big difference is putting dried carrot fibers in the epoxy makes it stronger. Let me back up and tell the story. My day job is material science R&D. So I have access to instrons that measure tensile strength, elongation, shear, and all that stuff. I wanted to check that 6mm underlayment that slider recommended... and it looks really good performance wise in epoxy and e glass. Now throw in a percentage of dried carrot fiber in the epoxy, and the physical properities improve by quite a bit and the laminate is lighter. Because the carrot dust is less dense than epoxy. I'm working on optimizing the dosage for strength and weight.... This technology has been patented however, and is sold for use in fishing rods I believe. But carrots are way cheaper than carbon nanotubes....

More performance, for less money, for more people....

OK, ill get off my soapbox now. Ill try to post the scantlings of this boat in a spreadsheet later this week. And ill see if I can figure out a way to get a acceptable Hull shape quickly and easially...

 

I'm in for that recipe. I'm messing with a Gary Dierking Tamanu based cat with the assumption that my $600 dollar Hobie 18 + the Tamanu cat can be a better camp cruiser than the overwight pig of a H21SC. If you want to ruffle some feathers try to get in the Chi-Mac race in something that's that cheap.

Dan (in Chicago)

 

I like that. I wouldn't start with the Chi-Mac, I would try the LMSS solo challenge first. It's a 138 mile solo race that can be used as a qualifier for the Chi-Mac. Those guys seem to be pretty laid back. I had a really good time racing in the challenge last year and I hope to do it again this year.

Hey, this june there is a 50 mile 2 handed race the LMSS is sponsoring, you can do it single handed... it is an anniversary race for LMSS and they are hoping for 100 boats to sign up.. Now that would be a great race to enter if you were so inclined.