First one, of course, took a bit longer as we figured out the technique, but now, with two helpers, we can put 1/2 a hull together in about 4 days. The amas are a bit smaller, so that might save us a 1/2 a day if all goes well, but the epoxy takes the same amount of time to dry! Of course, we now have other projects we can be working on while watching epoxy dry, like putting the 2 pieces already built together.
We put both layers on dry, then pull up the second layer and epoxy it down, one piece at a time. I've been rolling a thinned layer of epoxy onto the ply before using the regular, in hopes of it soaking into the plies to help hold they ply together (I noted the posts about Tuffply delaminating a while back!). I'm using monel staples for the first layer since they stay in place. The second layer uses cheap staples, and lots of pan-head screws to hold the plies down and together. These all come out once the epoxy has set up. I also put a row of screws in the first layer right at the bottom edge (the more curved part of the mold), then start the next layer just above those screws. Otherwise, the bottom layer tends to spring loose if bumped or something.
Each piece needs to be scribed and cut. I made a simple tool to do the scribing: a piece of 3/4 x 1 x 8" wood. A small piece (3/4 x 1) of the 3mm ply is attached to this to follow the edge of the ply, and a hole just beyond the piece of ply holds a pencil for drawing the line. two pieces of wood 1" long hold the new piece of plywood the proper distance away so that the scribed line means only a small trim on the piece. I will take a few pics of the "device" and us using it.
Three people is really the minimum for building the hulls as it takes two people to force the plywood into shape while the third person either scribes it, or staples/screws it down. Four is good the day we glue the second layer on: same requirements, but then a third person just mixes epoxy. Of course, one or two people could do it with clamps...but the time factor would go WAY up.
Epoxy: I am using Pioneer Clear thinned to coat the plywood in the inside faces, and then not thinned for the glue-up. The gluing ability of this epoxy is stronger than the plywood....so no need for greater strength. The thick consistency is good for filling the space between the layers which is inevitable. I am using Cord Laminating epoxy to apply the cloth.... Here the extra strength and thinner consistency are of benefit. Of course, I am using WAY more epoxy than a chined, single-skinned boat would use...and epoxy is by far the most expensive part of building the hulls (sails and rigging will, of course, rival it).
I have never cold-molded a boat before, but have built several hard-dodgers for cruising boats using a similar technique. The difference is the dodgers had a simple curve, although rather extreme, so the thin plywood was needed to achieve the shape. The trimaran is not as severe a bend as the dodgers, but it is a compound curve, so you are "torturing" the plywood a little, and also cutting it in strips narrow enough that the "steps" created by the fore/aft bend becomes negligible.
If all goes well Thur. putting the vaka pieces together, I will start pulling my order together for sails (Hyde) and rigging and other parts (balikbayan box, with most stuff from Rigging Only, in Mass., US). I hope to be sailing in Feb.
"It isn't that life ashore is distasteful to me. But life at sea is better." Sir Francis Drake