Proper sealant/adhesive for watertight wooden chambers?

[wtarzia]

I am going to add watertight chambers to seal in most of my outrigger sailing canoe except for a cockpit foot well (the chambers will have plastic screw-out ports for access and ventilation; a view down into the hull of this boat is at wtarzia.com, click on "outrigger"). I will use some screws to fasten these plywood panels into place, but the since the screws will be going into 1x2 pine stringers I dislike using too many screws, which might weaken the stringers. Of course I need a good sealant, but I am wondering if among the polysulfides, silicones, and polyeuthanes (Boatlife, Sikaflex, 3M5200, etc.) there is one sealant that will also make a reasonable adhesive to let me keep the screws to a minimum.

I do not know if I am being overly cautious here -- the boat is probably fairly strong even without the stringers, I guess: built from 0.25 CDX fir plywood, 6 oz glass on outside (and inside bottom-to-waterline), and an inherently beam-like sharpie-hull construction -- though a lively outrigger sailing canoe can build up some respectable strains before it is knocked down. As a very amateur boat builder I do tend to over-build.

Any advice welcome. Thanks! -- Wade

[nautiguy]

Not to hijack the thread, but in a previous thread I became convinced to use plywood rather than plexiglass for a water tank that I need to build. So the question is the same except I need to know the best way to keep water in rather than out.

Norm

[Thorne]

To answer the first one, I'd say PL Premium or 5200 -- both are more glue than sealant, which should meet your needs as long as the hull and joint doesn't flex too much. For more flexi joints, sealants are better but won't hold quite as well -- those would be Vulkem116 or 4200.

Nauti - surely for a water tank you'll be fiberglassing the interior? So I'd use epoxy to seal the edges as well as the surface. Others will know more, as yours is a different question than the thread poster's.

[wtarzia]

Perhaps since water pressure would be forcing the panels into the stringers, something more sealant than adhesive is OK for my watertight chambers?

[kc8pql]

Not to hijack the thread, but in a previous thread I became convinced to use plywood rather than plexiglass for a water tank that I need to build. So the question is the same except I need to know the best way to keep water in rather than out.
Strongly suggest you get a copy of the Gougeon's boatbuilding book. It has a chapter devoted to designing and building ply/epoxy/glass tanks. I built four 25 gal. ply water tanks for Alaya. They're holding up just fine.

http://i30.tinypic.com/jjv440.jpg

[nautiguy]

Thanks Kc. I'll find a copy somewhere.

Norm

[MiddleAgesMan]

The flotation chambers in my Goat Island Skiff are water and air tight due to the thickened epoxy used in the construction. How do I know they're airtight? When warmed by the sun (with the access ports installed), there is an audible whooossshhhh of air that escapes upon opening a port.

[wtarzia]

I don't want to use epoxy because I want the decks removable for maintenance -- at least more easily removable than cutting them out and chipping/grinding away the epoxied rim permanently adhered to the stringers. . -- Wade

[Chip-skiff]

I'm sealing bow and stern flotation chambers in a skiff with West System epoxy and the coating-type hardener (207, I think) so the wood will be fully coated. The decks will be epoxy-coated separately, then bedded in some sort on mildly adhesive caulk and screwed down. That is, they should come off with a bit of cutting and leverage.

I'm also installing those threaded access hatches (ugly, I know), so I can get to the fastenings and also dry out the enclosed spaces for storage without removing the decks.