Bud Boland wrote:

If you are putting a new bottom on a Chris Craft, plywood is fine to use but
DO NOT encapsulate it in epoxy. This is a terrible idea. If you'd like to
know why either contact me or invest in a book entitled "How To Restore Your
Wooden Runabout" by Don Danenberg.

Bud

"Klaus" wrote in message
...
Gary, one should never let a plywood hull absorb water if one wants to
keep the boat for a while.
Any wood will expand when it absorbs water, with plywood the waterproof
glue might stop the absorption past the surface veneer layer but I
would not bet on that. Water would readily be absorbed by the end grain
of plywood joins.
My plywood sharpie hull is fully encapsulated with epoxy + glass on the
outside and also paint on both sides. There is nil water absorption.

If your Chris Craft absorbs water you'd better fix that before the boat
rots away.

Klaus

Gary Warner wrote:

I know planked hulls absorb water and expland - do plywood?

How much water are we talking here? A few gallons, tens
of gallons. (22' Chris Craft 1958)

Thanks,
Gary


OK, nowfor my twopence worth.

Traditionally built boats **need** to absorb water to swell the planks and close
the seams. A plywood boat is NOT traditionally built.

Consider how water moves through wood: very slowly across the grain (otherwise
the brandy would leak out of all those 30-year old barrels), but very quickly
indeed along the grain, for which the tree depends for it's existence. When
water is in contact with the face of a sheet of unprotected ply, it will move
slowly into the veneer, well, not that slowly actually, and once in, will run
very quickly up the sheet. It will have a damn hard job crossing the first glue
line if it's good ply. Once in, it will swell the veneer across the grain,
testing the glue line, and the demon rot will commence. Don't let it in!

I'm building a boat cold-moulded of good BS1088 ply; three layers. Outside will
be a skin of 10oz glass/epoxy, and several layers of good paint; inside will not
be coated except with a vapour permeable preservative, so any moisture finding
it's way in, at least will have a way out again, if I'm lucky!

A reputable boat-builder I know who has 25 years of experience in epoxy-wood
construction, uses just one thin coat of epoxy in the bilge, and clear varnishes
it. Then the surface of the wood can be seen, and thus any discoloration that
might result beacuse of water penetration, so the problems gets fixed early,
rather than later.


Beeswax