Solid Wood vs. Plywood Keelson

[Gary Davis]

I'm curious about the use of solid wood vs. plywood for keelsons in small plywood lapstrake sailboats. John Brooks uses solid wood for Ellen (12') - at least in his book, and Doug Hylan uses plywood for Beach Pea (13-15'). Maybe these designs aren't a valid comparison, but in general, what are the pros and cons of using a solid wood (douglas-fir) keelson and gluing it to plywood garboards? Is there some design consideration that makes one more appropriate than the other? Are fasteners necessary?

Thanks - Gary Davis

[Thorne]

Do you mean "glue it to plywood bottom" instead of "garboards"?

Hard to say, as for me much would depend on what else would be fastened to the keelson. Solid DF will take multiple fasteners with less work than ply, as you don't have to pre-drill and fill with epoxy. If the boat will be sailed without floorboards covering the keelson, solid wood might also take the wear from gear and sandy shoes better without opening up plies to rot.

But I assume you would have to use a few fasteners as well as a flexible glue to attach DF to a ply bottom.

[mcdenny]

That fir (or mahogany variant or sassafras - not oak) keelson will be much more plesant to plane down fair than it's plywood counterpart. Usually a lot of fairing is required.

The fir will add more longitudinal strength as all the grain runs the same way.

You can probably get one piece of fir to do the whole keelson while the ply will have to be scarphed if the keelson is more than 8' long.

No fasteners are necessary for a design meant to be constructed with epoxy. You will probably have to screw down the second garboard while the glue cures, though. It's easier to back the screws out before the epoxy is really hard - say after about 24 hrs cure. YCTMV Fill the empty screw holes with epoxy.

[Ed Armstrong]

I agree with Denny. My Acorn dinghy used a solid wood keelson to which the marine plywood garboards were glued. I backed up the epoxy with a few screws for peace of mind. Planing the solid wood keelson/hog bevel was much more pleasant than shaping plywood.

Ed

[JimConlin]

I've used laminated keelsons which were all or part plywood. Such a laminate wouldn't have the longitudinal stiffness of one made from solid stock, nor hold screws as well, but it is stronger and stiffer athwartship and on a glued lapstrake or sheathed strip boat without much lateral framing, it might be preferable.

[Gary Davis]

Thanks all. I'll go with the DF.

Gary

[peter radclyffe]

plywood is weaker in tension, which is why its not used in keels & masts
its better in compression