Location: Virginia, US Umm, if anybody wants to give advice on those tube brackets, still grateful, although I think I have it pretty much figured out. I want whatever design gives enough strength and a good right angle so the angles of both beams will be the same and not concentrate stress more than otherwise and tend to tear the ama up when loaded! Originally Posted by BWD Umm, if anybody wants to give advice on those tube brackets, still grateful, although I think I have it pretty much figured out. Then I would still use Al since I can't afford CF, but do a design around straight tubes with no welding, and build composite brackets to secure 'em.
Posted a query on the metal boat building sub-forum about using gently bent tubes instead, and I will try to go that way, keeping Al strength and saving weight and complexity. I used a local guy in a small town (Fallbrook, CA), but he has a pretty decent metal fabrication business (not just welding). Currently I am fiberglassing the interior, but I am trying to design a folding beam system that is fairly simple yet strong enough to withstand the forces that it will see once it is out in the ocean.
Originally Posted by erikhaha Here are a few pics of the vaka that I am building, which will eventually be a trimaran. Basically I used the Ulua shape which I got from the book but I scaled the dimensions to give it a little more volume, wider, deeper and longer (20').
Location: Virginia, US What are you guys trying to shame me into updating my thread or something?
Vaka structure done (a good while back) minus a thwart and beam mounts -waiting to see if vendor can deliver bent Al tubes I want with strength.
I can understand that a bent beam with a nice curve, be that metal or wood does look nicer. In the water I found that the outrigger has very little drag when compared to the main hull.
Glad the rendering shows nice; the real thing as you can see still currently looks like a chunk of foam with a rocker to it.
It's been fun to work through things, but had I bought a plan a couple years ago I am sure I would have had a boat much, much faster.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. In the interests of reduced drag, I'd always subscribed to a steep-angled hull profile for the ama's, due in no small part to its popularity amung employed boat designers.


But a thought crept into my head: a steeper shape dives deeper, and youhave increased surface area interacting with the water when heeled over, which means more drag. Originally Posted by Fanie You have to exceed a certain speed for a hull to plane, depending on the weight also. Location: Cocoa Beach, Florida SA, Frank Bethwaite designed some high performance small trimarans with relatively short ,amas with a flat back end that planed. 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. It's not a traditional canoe design, though I'm not sure it's hull is different enough to merit a change in philosophy. Dough, that 2nd picture of yours - I can see 2 of those ama's and the small sail just so you don't have to row.
Originally Posted by Fanie I think that flat hull or near flat hull was designed to plane ! The logic of widening the beam is sound, however the aluminum aka's weigh more than the foam of the amas, plus she should come about easier with a narrower beam. Location: North America Put the flat side of your amas out so you get a little lift while you're heeled over.
Originally Posted by DrCraze Put the flat side of your amas out so you get a little lift while you're heeled over. I'm actually trying to come up with ways to lengthen tose amas and strip the wood from them. Obviously if an ama is the only hull in the water then it is best to fit the rudders and dagger boards to the amas rather than the main hull. Still want to do them of aluminum that will be light and can be used in a more or less plug-in manner (ok, 4 bolts and one string ). If you went for simple straight beams and then had some connections going down to the ama, the extra weight would only be 3 or 4 kg at best.
Mine is 14ft deep Vee plywood, overly built, approx 40cm wide, approx 40cm deep, volume 220L.
My thinking was that for a tacking outrigger a littel extra weight in hte outrigger does no harm. Done it will displace 200 lbs and weigh around 20, minus the connections, which I hope will be stubs to take bent Al tubes.


Something with a somewhat flat bottom that becomes more effective as the boat leans on it harder?
It also seems as though the ama under the wing isn't loaded, since the wing seems to be meant to provide vertically neutral force. 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! I know there's a gross oversimplification in this allusion but I think it gets the point across. The normal way to do it, without a bent beam of course, is to have a straight beam and then struts going down.
I'm a firm believer that there should be no place on a boat that you cannot step, so I'm making it good and sturdy. They weigh more than double what they need to weigh at only 8ft long, but I'm pretty sure they could pierce the hull of most Bayliners.
If I spun them 90deg, I'd have the psuedo-flat bellied Ama that I mentioned in the first post. With a V shape ama, the struts can come up parallel with the ama sides, so that at beam level they are a bit wider. Would I then need a centerboard keel, since the amas would be slipping across the top of the water?
The theory is (as long as I'm handling the boat right) the load on the ama will increase right along with speed. A suggestion: go with as much cross arm clearance and beam as you can-the more beam the smaller the ama has to be. Your connections can start narrow at beam level, and then get wider as you go down to connect with the outrigger.



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