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Old 04-16-2007, 07:52 PM
finnyct90 finnyct90 is offline
 
Join Date: Apr 2007
Rep: 10 Posts: 1
Location: Hudson Valley
Tri Hull Advise needed

I am curious about designing a tri hull for our local “wacky raft race” held here on the mid reaches of the Hudson River. I and 3 co-workers (all with lots of time on the river) were talking about entering this year. Typically entries just need to be homemade; most are some type of raft like structure. This year, we would like to beat everybody!
So here is my idea, Large diameter 16” or 20” PVC sewer pipe with sealed end caps for the center hull, smaller 6” or 8” PVC pipe for the out riggers (I know that there is a proper name starts with an A). I was thinking of using “tee’s” to connect the out rigger arms (spars?) to the center hull. The arms or supports could pass through the center hull and be pretty strong. We have a whole roll of that orange safety fence for the trampoline! I need to think about some type of lee or dagger board and rudder. We have lots of steel and a welder in the shop.
I am thinking about doing a lateen (picture a Sunfish) type of mast and sail arrangement. Mast might be some heavy wall 3” pipe we have and the sail may be a couple canvas drop cloths stitched together.
The race is one way on the outgoing tide so as long as you stay afloat you can finish the race. The prevailing winds will put us on a long reach, almost but not quite straight down wind. It would be really cool if we got a little up wind capability out of it but it’s not that important (if all else fails, we’ll paddle with our uke’s)

I come here asking for any “rule of thumb” advice, hull length vs. mast placement, sail area. Etc. The raft needs to carry four middle aged, balding, fat guys with refreshments about a mile down river as a minimum. As a maximum it could carry us down to the finish, come about and tack through the fleet a couple times. Please let me know if I should abandon the whole idea and start looking for drums to build a raft.

Thanks in advance
Finny
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Old 04-16-2007, 10:19 PM
mcollins07 mcollins07 is offline
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Join Date: Jan 2006
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Location: Texas
Sounds like fun to me.

You would probably get better sailing characteristics using two large pipes. If you use three, then you are moving into trimaran design which might be a bit more difficult with simple PVC pipe. Also consider a couple of aluminum ladders to lash the pipe together. The ladder will be more rigid. Stiffness should getting better sailing performance. Do you have 20" PVC pipe available? What is the cost? I calculate 2 x 20' x 16" as about 3500 lbs, divide by half for a practical pontoon. That's about 1700 lbs for the boat and passengers. I don't know what the pipe weighs, but my guess it should work. Two 20' sections of pipe at 10' across the beam would probably work very well. Tyvek is a light weight insulating wrapping for houses. It is commonly used for cheap sails and might work better than canvas.

Using a displacement to sail area ratio based on a Bruce number of 1:

SA = ( Displ.)^2/3 = 142 sq feet.


Let us know how it goes.
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Old 04-17-2007, 01:57 AM
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alan white alan white is offline
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Sounds like enormous fun!

Something like culvert pipe, maybe a half inch thick, 24 ft long? The ends should be pointy, which might call for some clever origami.
I agree with the simplicity of a catamaran. Each hull could have a sail buried to the bottom of the hulls (you've got four guys, after all).
That would be a panic! Two teams with independant rigs! Each with their own cooler! It's priceless!

A.
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