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