Folding DIY Trimaran with a Major Hull Redesign
In this post, Frank Smoot shares another update on one of his DIY Trimaran models. And it’s very cool.
Wait until you read about how this new small trimaran handles :-) Some new photos of the hull are included below also.
You’ll be able to hear Frank talk with Jim Brown a little about this hull re-design next week in an audio clip. The entire interview is now a part of the “Multihull Conversations with Jim Brown” series.
He wrote this short article especially for us guys here at smalltrimarans.com too. Thanks Frank!
Folding Tri: Major Hull Redesign
By Frank Smoot (AKA “The DIY-Tri-Guy”)
The original design for my 16′ folding tri (as seen in the “Can Your Trimaran Do This?” video) had a double-ended hull. Why? Just as an experiment, really. Since all my other tris all have had transoms, I wanted to see how a “pointy” rear end would sail.
Well, it had some pretty big drawbacks. First problem was that it “hobby-horsed” in any kind of waves. I guess you’d call it “pitching.” Not comfortable, and probably hurt performance as well. Second, the rear end tended to squat at higher speeds, due to lack of flotation aft to help keep the bow down.
But the biggest problem was the helm. That double-ended hull was almost impossible to get balanced. At first it had a huge amount of weather helm. So I added a skeg, but that gave me a ton of lee helm. I spent a LOT of time trying to trim that skeg so the helm was balanced. Turns out that just 10 square inches of skeg area was enough to cause either lee helm or weather helm. That’s WAY too sensitive! And for some reason, the rudder always requited a ton of effort.
So back to the drawing board, and now I knew just the kind of hull I wanted. My first “real” tri (No Commotion) had a fairly sharp V-hull with a deep forefoot and an average dihedral of 30-35 degrees, a moderate transom, and just 2″ of rocker. It was smooth, fast, very dry, and tracked like a train. But it didn’t like to come about.
My wife Laura’s tri, on the other hand, had a “5-piece hull” — a flat bottom, two 45-degree bilge panels, also 2″ of rocker, a moderate transom, and vertical sides. It was also quick and would turn on a dime, but wouldn’t track at all unless the leeboard was down, and tended to pound just a bit in waves. Fast in light air, but not good in very shallow water.
The solution, I believed, was a shallower V-hull — something that was a blend of the best characteristics of Laura’s boat and No Commotion. This new hull got a moderate transom, slightly angled sides, and an average dihedral of 20-25 degrees. I bumped up the rocker to 3 ½ “, just to see what would happen.
Conclusion: If there is a “perfect” shape for a non-tortured plywood hull for a small tri, this new one has got to be pretty close. At least it’s as close as I have gotten. This hull is smooth sailing, quiet, fast, and dry. It doesn’t pound in waves, and is quick in light air.
Best of all, it handles beautifully. It points better than any of the other boats, and gybes with zero drama. You can literally sail continuous figure eights or 360 degree circles in any direction or wind speed — the kind of handling I really hadn’t thought possible in a small tri. This boat puts a definite smile on my face!
Of course, the folding amas and E-Z-Up mast & sail rig also help quite a bit. Being able to start sailing less than 5 minutes after I get to the beach is a total delight, especially when I think about the countless hours I’ve spent assembling earlier tris after taking the hulls, amas, akas, etc. off the trailer. I finally have the 16′ tri I always wanted. Now if I could just find a professional sail maker to make me a “real” sail in place of that white hunk of stretchy white polytarp I’m currently using…