Small Trimaran; Ama design?

I think this is where i break away from racign designs... for now. This canoe'maran will never fly the central hull, so I won't be relying on the Ama's to be the only wetted area.
http://catsailingnews.blogspot.com/2010/04/new-class-design-dna.html

From what that says, the bow shame s meant to be a wave peircer when flying the hulls. Basically, that bow *is* going in the water when she's at speed, they may as well make it cut better. Thanks for all of the tips, I'm plugging some things into Pro-E to try and get a model going.
This was the initial design that popped into my head last fall. The ama profile there is the same as teh dive rig pictured above.

I mean to find out. That's the nature behind my screen name; I'm not using science practically or professionally, I'm using it for fun... Since it should be used for the greater good, I consider this abuse.
Though anything with the canoe attached will be a pig, I always have the option of removing the ama's and using them somewhere else. At some point I'll be ready to make my own main hull, at which point it would be nice to have the "high-performance" ama's already made to go with it.

 

Planeing amas mgiht work on a high speed boat, but the canoe is definitely not in the planeing realm. So if you design the amas with a planeing planform you will be shooting yourself in the foot.

 

There are two ways to go about it. First is to put a really big oversize sail on it, which will make it tender and you have to be prepared to do some swimming and uprighting a lot.

Second would be to get the oversize kite. If you can control it properly you can get on the plane in wind even it you're sitting on a dustbin. Such a kite makes very nice lift, the ama's will never go under.

 

Well, if you go through the forum you'll see how many abusive buggers there already are It is only for the greater good if you put up some pictures and video's so we can all enjoy in your science. It's always exciting to try new stuff out, and amazingly some works better than expected.

I like the idea of the foam-core wing sail. You can put one on each ama and two on the main hull.

 

A little science...

As I said in my first post I don't think planing amas would work too well on a "normal" canoe. However, a little science shows that "hull speed"(1.34 X sq.rt. LWL) for a 17' wl canoe is 5.52knts.
The planing threshold(2 X sq. rt. LWL) of a 4' "ama"(designed as a planing hull with appropriate shape) is 4 knots......
Food for thought.......

 

thanks for this, these are the sorts of things I'm hoping to learn here. Hull speed calculations aught to be fairly accurate in the case of the "scanoe", since the hull is so basic in its shape. To get more accuracy, I aught to weigh the additional "sailing stuff" and load the boat up, with me in it, to see where the waterline will be.

The Amas will will be shorter than the boat itself, would it be best to have them biased toward the front of the boat, toward the stern, or neutral about the center of gravity? I'll be positioning the sail so that it's windload is centered amidships.

 

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Remember, a skinny longer ama(14/1 or narrower) will be able to handle the canoe's hull speed w/o too much drag thruout the speed range and is probably a better choice.

 

He he... The ama's will always keep up with the main hull

 

If you wanna go real fast on that canoe fit it out with some leeboards and a hiking board. Just one thing...you'll get real wet too.

 

Getting wet may prove an issue, depending on how well my boy can operate a bucket. The canoe isn't a self-bailer, if she leans a bit too far she'll probably swamp entirely... thus the trimaran.
Along those lines, though, this came to me this morning:
http://img708.imageshack.us/img708/4420/projection.png
Leeboards fixed at an angle, so they penetrate a fair amount of water when heeled over, yet contribute very little to the draft.

I really lucked out this week, I found a fella on Craigslist with a heap of aluminum extrusions. For $150 I got:
2x 24ft long, 2" od, 1/8" wall (main mast, Aka's)
1x 11ft long, 2" od, .062 wall (boom)
1x 11ft long, 2" od, .062 wall (tiller, misc)

The tubing supplier I'd been talking to couldn't get anything over 12ft in length.

 

Nice project. I have thought of doing something similar myself with my kayak.

One thing is you are putting your amas on the wrong way! The flat side goes outward.





Look at a hobiecat. It is done this way to reduce the need for centerboards. The flat side acts as the board.

 

Thanks for the tips and the visual. This isnt the first timei've heard it, so I'll deffinately be trying it that way. I've been puzzling over the best way to mount a centerboard, or a small fin on each ama. If I can get around that, it would save some labor and make beaching easier.

 

I would certainly just try the amas with flat side out first. It works fine on a hobie which has no boards. At the very least it would reduce the size of the board needed.

 

Solway Dory makes a double outrigger sailing canoe

There are 2 models, one is called the Osprey, the other.... something else. Looking at teh photos, the osprey looks as though it has amas about 10ft long.

The other model has shorter amas. There is a video of 2 of these small trimarans sailing along. Unladen weight is approx 80kg for the 16ft Osprey double outrigger. I have looked at it, and it seems a pretty good setup.

My suggestion would be, just copy 100 percent what Solway Dory did with the Osprey, their outriggers look to have a very nice shape to me. (I have built 3 outriggers for various single outrigger canoes, well 5 if u include some very small outriggers) If u live in the UK u could buy one, an Osprey that is.

link is here
http://www.solwaydory.co.uk/

from memory I don't think they sell plans unfortunately, but i may be mistaken.


n peter evans
www.tacking-outrigger.com

 

Here's my own experience for what it is worth:

Years ago when I knew squat about sailing I put a single flat-bottomed 7' x 8" x 8" ama on a conventional 14' fiberglass canoe with about 35 sq ft of sail, plywood leeboard and rudder. Sailing was not very exciting, as you would expect with such a small sail, and I had added a seat on the gunnel so the ama was well down in the water. One day I found myself gliding along much faster than usual, looked around and realized that the ama was clear of the water.

That, to me, is the key to the whole thing. With a pair of amas it is easy to balance the boat so the amas are clear of the water in which case their shape is irrelevant. They are only there to add static stability for fishing and while you are stomping around raising the sail and such, and to provide backup stability when you get caught by a gust.

Just make sure they do not have so much drag that the boat slews violently when one touches the water at speed, and they'll be fine just hanging out in the breeze. Long skinny amas are probably best mounted bow up so they enter the water gradually without digging in. Just make sure they are high enough that you can get both of them clear of the waves.

From a practical point of view, deep amas would require high-mounted beams or curved beams to get the amas above the water, shallow hulls on a straight beam would be simpler; if I did it again I would try mounting the amas on a single beam, with a short wide vee-bottomed ama hull to minimize torque on the beam. IMHO most people make the amas too large: I know I did; it never got even close to being pushed under the water and could have had its buoyancy reduced by 2 or 3 times. Crew weight does most of the work of balancing the sail's heeling moment.

A last-minute thought: there is no reason why the amas have to be identical: why not try out 2 different designs at a time to see which works best?