I know PAR weighed in on this topic within the last year, but I'm going to ask again. If a keel is laminated from marine grade plywood, given the wood's stability, can it safely be fiberglassed? Just looking ahead..!!
Dave
Yes, but only in a perfect world. Dimensional stability is only part of the equation. The reality is plywood isn't as strong longitudinally as solid wood, though it stronger across the grain. This isn't the main issue. The biggest concern will be moisture getting into the end grain of the plywood. In the perfect world, this can't happen, because you've used 3 or more coats of epoxy. In our world full of rocks, shell covered beaches, floating logs and other debris, not to mention bouncing it on the trailer roller supports or frame rails, the keel takes a beating. Unless your 'glass job is a 1/2" thick, you're going to crack, scratch, ding and other wise breach the sheathing. You know what comes next when the water gets at the mashed end grain.
Thanks, Paul. How would you construct a plywood keel for a Weekender/Vacationer?
Dave
I would use a stack, just like the plans, but with plywood and I'd also incorporate a solid wood shoe the full length of the keel. This would help protect the plywood end grain. Of course, I wouldn't make a plywood keel, but that's how I would if I did. And if I was making this level of a change, I'd probably add a few inches of draft and radically change the profile too, for improved pointing ability and much crisper maneuverability.
When I did my plywood keel (Hi Paul! - you knew I'd chime in here) I laminated 3 layers 3/4" plywood together. I know of others who used thinner plywood to get more laminations. Using 3 sheets I was able to get as few joints as possible in the outer laminations. The inner lamination had more joints. I just but-jointed the pieces rather than scarfing.
Rather than try to mimic the 1X12 in the plans, I incorporated the deadwood, stem, and stern post into the layout as much as I could. One other thing that I did - which I would suggest for anyone, was to build in the hole for the cockpit drain, embed the fitting for the bottom rudder fitting, a bow eye-bolt, and put in a plastic tube to allow for fishing wires for a bow light.
After assembly, I fiberglassed the keel while it was able to lay flat and then bedded a steel strip on the bottom that went up the stern-post and stem.
I know of other plywood keels that have lasted well with care - mine is several years old but has only been wet a couple of times.