Small Trimaran; Ama design?

[science abuse]

Great tips, Kayaker, thanks for uploading your experience!
It seems fairly logical that the boat will perform better with less stuff in the water.
I guess I should clarify the ereason for a trimaran: I want to have a few people on the boat and still be stable.

Everything I own and build serves at least 2 purposes, and I'd like this boat to do the same.
1: Daysailer. I'd like it to safely haul myself and my boy, and possibly two additional adults, witout being cramped. I've seen a few specialty built sailing canoes, and they're basically lee-boarded Lazers by the time they're done building. An open hull, wide stance, and some tramps should make it tip-proof and much less cramped, and keeps me from shouting at folk to move around for every gybe. The large'ish sail should give enough power to move the weight, and low drag ama's slow us down less.
2. Empty boat fun-sailer. With just myself in the boat, I can move around and balance her out as needed, and the big sail and slippery ama's will contribute to forward velocity.
3: Fun project. Keeps my mind and tools busy for the purposes of improvement rather than just maintenence.

Cranking out something that works would only take a weekend. Making something that would be fun and interesting for a few years is taking some planning.

[ancient kayaker]

I was just looking at # 2 and 3. They are in the range of what can be done in a weekend or 2.

#1 is something else. I did take the missus out in the canoe (on an athletic scale of 0-10 where 0 is an arthritic rock she is about a 1) I didn't have to ask her to move around. However the extra weight slowed the boat down to a crawl so the additional sail area will be needed.

An average canoe gets crowded pretty damn quick if people wanna mill around and not just stay put and paddle. It might be easier to strap 2 canoes side by side to make a cat, which would have more performance and space.

[science abuse]

I'd actually considered putting my 'ol Snark sunflower on the end of the aka's, two sails are better thanone, right?

I don't think I have the right materials to mount a sail on a cat. The mast is curved to follow the shape of the Escap Rumba sail I'd picked up, so it can't really be stayed.

[fishing buddy]

I have a Coleman Scanoe as well. I use it for river fishing and power it with a 5hp outboard. I can get up to 11 mph but would like to go faster. I have been reading about outriggers, hydrofoils etc. and was wondering if something like your Science Abuse's design could be used to safely get this canoe up on plane.

Could one use outriggers made from fat water ski's or skurfers (precursor to wake boards) or small surfboards to assist the canoe hull in planing? More like a hydrofoil i guess.

Something along the lines of this http://www.nielsensoutriggercompany.com/Features.html but maybe more surface area, less buoyancy.

[science abuse]

I don;t think you're going to get a real speed benifit from adding more wetted area. It's a long narrow boat, so planing is going to be difficult to do in a safe and stable fashion.

Does yours have "strakes" on its belly like mine? They're ment to help it track better, but might be used to help planing:
Fill them in to amidship, with a sharp step where the filling stops.

BTW, I've breifly entertained the idea of cutting the transom off and basically stuffing the back half of a Jets Ski back there. It's a horrible idea, but it seems fun.
I was inspired by this, though with a mono-center hull:
http://www.boatdesign.net/gallery/sh...php?photo=8690

[fishing buddy]

What about flipping her over, filling the chanels with wood, then attach a plywood "wing" with no edges effectively widening the stern of the boat under way, allowing plaining. Would you have to add sides to the wing extending above water line, woul it have to be enclosed fully(basically a boat on a boat?

How would you temporarily attach to boat for testing (no holes in hull) ?

[fishing buddy]

Basically the last 8' of a 40" Jon, with the transom cut out unless absolutely needed for saftey.

Of course at that point just buy a Jon to begin with.

[oldsailor7]

The Piver "Frolic" (16ft), had flat bottom amas, rather like a water ski with sides.
It was very fast and fun to sail.
It was 8 ft wide with solid decks and when hiked out at full speed I am sure the lee ama planed. Jim Brown had one and I am sure that was what sold him on multihulls, ----and the rest is history.

[upchurchmr]

Doug,
What was the book you posted the planing tri from by Bethwaite?

Originally Posted by Doug Lord

SA, Frank Bethwaite designed some high performance small trimarans with relatively short ,amas with a flat back end that planed. His amas were designed ,primarily just to aid static stability but as you can see in the picture could help a bit at other times!
My personal opinion is that, on the type of boat you're considering, a narrow14/1 ( Length divided by beam) ama hull might work best since it is unlikely that a standard canoe hull will go fast enough to have an effective planing ama.
Now, if you had a powered up international canoe type boat then a planing ama might be worth considering if you didn't want to use the sliding seat, trapeze or rack. The IC has about 100 sq.ft. of sail on a 17' hull-some also use spinnakers.
Once you decide on the sail area you can experiment very easily by using something like a carbon or much cheaper aluminum tube
and carved styrofoam "hulls" to find out what works best with your boat. You can use a thin piece of plywood as a center "keel" with styrofoam on either side, hand shaped. Probably won't even have to glass the styro until you've found a shape you like. This allows very inexpensive experimentation.
Good Luck!
---------
Click on image, then click on resulting image for max size:
HSP
kayak with single aluminum crossarm-these amas appear too short to me(higher drag than longer/narrower)

[Doug Lord]

Originally Posted by upchurchmr

Doug,
What was the book you posted the planing tri from by Bethwaite?

============
Frank Bethwaites "High Performance Sailing", page 181 and there is another pix on page 261.

[upchurchmr]

Actually I have the book, just forgot the picture.
Thanks
Marc

Originally Posted by Doug Lord

============
Frank Bethwaites "High Performance Sailing", page 181 and there is another pix on page 261.

[hospadar]

Originally Posted by science abuse

Follow up question: what is the logic behind the bow disign of modern multi-hulls? seems upside-down compared to conventional designs.

There are some canoes with a sturgeon nose (or ram bow) like those amas, and a lot of warships are designed that way. I gather it's supposed to be more stable in waves, since presumably waves won't slap the bottom of the bow (as much) and bounce it around. That said, I am not a professional hull designer - I suspect that for an ama, the difference is probably pretty minor until you get to a really high level of performance, and that wetted surface, length, and weight are going to matter way more than bow angle.

Perhaps more importantly, sturgeon-nosed bows look really cool, and what's the point of building a boat if it doesn't end up looking cool?

[upchurchmr]

No a lot of warships are not designed that way. A few recent ones which are suppose to have a low radar signature have done it.

[hospadar]

Also some older ones with tumblehome topsides.

but yeah, maybe "a lot" is a bit of an overstatement

[Doug Lord]

More on reverse bows here: Wave Piercing Bows