Small Boat/laminated ribs?

[Vastbinder]

So, tell me... on a 10-15 foot wooden/fiberglass boat, how well would it work to construct the ribs and perhaps the keel from laminated 1/4 inch plywood? (I mean laminating several strips of 1/4 inch ply to get the thickness one is after)

I''m talking about a cheapy boat made with basic materials and then sealed with dynel and resin.

[Jeff_H]

If you are going to laminate frames, it would be cheaper to steam bend the ribs out of solid stock or to laminate the frames and keel out of regular lumber. Decent grades of plywood or relatively expensive. If you are really building a cheap boat that small and you can build the frames out of blue foam and then use epoxy and fiberglass as the structure. On the other hand 1/4" plywood works well as planking stock and bulkheads on a boat that small.

Jeff

[Vastbinder]

Yeah, I''m going to be using basic "home improvement" grade plywood. I just wondered if the laminating/sealing technique would hold up.

[Jeff_H]

Generally exterior grade plywood will not hold up very well, even if coated with epoxy. While the glues are similar, exterior grade plywood generally is allowed to have a larger number of voids and uses poorer grade veneers and lower heat and pressure. As a result even when coated moisture will permiate deep into the wood by way of the voids causing the boat to rot or delaminate. That said, I have built a number of disposable prototypes over the years using AC grade exterior plywood and coated them with epoxy.

Jeff

[Vastbinder]

and how long did they last?

did you use a single coating of epoxy, or multiple? Also... did you seal the inner surface as well, or just the outer?

just wondering, so I can know what to expect.

[maxcontax]

If you are using home construction grade plywood expect the boat to leak. For the time and effort you are about to put into this, go the extra few dollars on good marine plywood. When it''s done, 100 hours later, you''ll have a project to be proud of. Life''s too short to spend it with an ugly boat, making excuses for it forever.

[Jeff_H]

If the original poster is going to sheath the boat in glass, it is unlikely that it will leak. It just won''t last very long.

Jeff

[paulk]

Beyond the voids allowing any moisture that DOES enter to migrate that much faster and develop rot sooner --(It is a boat- there is going to be moisture.) -- voids that are prevalent in the interior plies of standard plywood will create weak spots that WILL cause problems later. If you''re just slapping together a rough& tumble skiff, it will likely be quicker & easier to cut ribs from standard board stock (try to orient the grain along the rib as best you can) and use higher grade plywood so it holds up better.