alkorn

All the instructions I've read for sheet plywood boat construction insist that I cover the exposed edges of the plywood either with battens or with fiberglass and epoxy. Just coating the edges with non-reinforced epoxy isn't supposed to be good enough. Then I read descriptions of glued lapstrake plywood construction, and practically the whole bottom of the boat consists of exposed plywood edges. Epoxy coating the edges is recommended, but there's no way to glass over the sharp corners. Why are exposed plywood edges bad in sheet ply construction and OK in lapstrake ply construction? From what I've seen of the performance of plywood edge grain, one landing on a rocky beach could leave plank edges on a lapstrake ply boat with lots of little splinters torn out. My experience is with ACX, not marine, but I don't imagine marine edges would be strong enough, either. I think I'm missing some important info here. Can anyone help out?

Tom Lathrop says " The idea that you should epoxy only one side of planking to let the wood breathe makes no engineering sense." I think he's wrong there, though I admit that "let the wood breathe" is not a good description of the reasoning behind the outside-only school of epoxy application. The idea is this: The outside of the boat is usually WET. The inside of the boat is usually DRY. If you epoxy both sides and then get a small hole in the outside epoxy, water will get in and be trapped there. If you epoxy only the outside and then get a small hole in the outside epoxy, the influx of moisture through the small hole is compensated for by efflux of moisture through the fully open inside surface. Moisture doesn't build up. The same sort of reasoning applies in installing house insulation: you put the vapor barrier on the side where the air will be moist, and put NO vapor barrier on the dry side. It seems to me the main counter-argument to this is that the bilge of a boat isn't really dry, so you're better off with epoxy on both sides. My preference, though, is for epoxy on the outside of plywood only. In hidden spaces leave the inside wood bare or apply preservatives. In exposed spaces paint, since paint is much more permeable than epoxy.

I've just started building a Stevenson Triad and want to use some rig other than the standard lateen. I have two reasons for this: I don't find the lateen rig very attractive, and I'd like to get more sail area onto the boat. Based on the Stevenson plans, I've drawn up the Triad with the lateen rig (http://filebox.vt.edu/users/alkorn/Triad%20Lateen.pdf). The center of effort of the rig appears to be almost directly above the centerline of the daggerboard. I found this suprising, since from what I've read the center of effort should be a little forward of the center of resistance to avoid excessive weather helm. The only way I can think of to explain this is that with crew in the cockpit the stern sits low, moving the center of resistance aft of the daggerboard. I'd like to hear from anyone who's sailed the Triad with the standard rig. Does it show weather helm? Anyhow, I've drawn up a gunter rig (http://filebox.vt.edu/users/alkorn/Triad%20Gunter.pdf) with 82 sq ft area as opposed to 66 for the lateen. The center of effort is on the same line as that of the lateen and only about 7 inches higher up. It seems to me this is the most sail area I can get on the Triad without either moving the center of effort futher aft, using a mast longer than 12 ft, or adding a bowsprit. I've also drawn up the gunter rig reefed (http://filebox.vt.edu/users/alkorn/Triad%20Gunter%20Reefed.pdf) down to a total area of 57 sq ft. Unless I get serious advice to the contrary or get a better idea before I finish the hull, I'm going to rig the Triad with this gunter setup. Any and all comments and advice will be appreciated. I'd especially like to hear from anyone who has experience sailing the Triad. (Incidentally, I drew up these plans with the "Instant Architect" CAD package I bought my daughter last year. Though it is really meant for designing houses, it has some nice features including automatically faired lines, automatic calculation of areas, and automatic calculation of centroids.)