On Oct 27, 7:08 am, Jean-Francois Dockes
wrote:
salmobytes wrote:
Plywood that stays in contact with
the water will eventually get nicked or dinged. Water will migrate
into the plywood and then you're toast--well, soggy french toast maybe.
At that point you have to grind off the fiberglass and move to Arizona
for a month or two.

This must really sound weird to the thousands of plywood sailboats
owners. There are plenty of 30 to 40 years old boats still sailing. Well
painted marine plywood is very durable.

I was talking about marine plywood skinned in fiberglass.
The fiberglass will eventually get cut or broken. And then
moisture will migrate in the plywood core. This happens a lot
faster on driftboats than sailboats. But the process is inevitable,
at least for plywood that stays in contact with the water a lot.

..........and even then I was talking about hulls
made with plywood that is skinned on *both* sides
with fiberglass. Hull that have fiberglass on the outside
and a paint or oil finish inside can more easily dry out.

I've seen driftboats--with 'encapsulated' epoxy fiberglass bottoms--so
saturated with water their weight was almost double. If you do
build that way you have to keep up with the repairs, adn patch
dinged fiberglass almost right away (not all that hard to do,
but you must do it).

Or you can build with honeycomb core. It's bullet proof and fool
proof,
almost. You can pre-fiberglass honeycomb core while it's still
flat, on top of visqueen covered saw horses, and then treat it
like plywood.

On Oct 27, 11:35 am, salmobytes wrote:
..........and even then I was talking about hulls
made with plywood that is skinned on *both* sides
with fiberglass. Hull that have fiberglass on the outside
and a paint or oil finish inside can more easily dry out.

I've seen driftboats--with 'encapsulated' epoxy fiberglass bottoms--so
saturated with water their weight was almost double. If you do
build that way you have to keep up with the repairs, adn patch
dinged fiberglass almost right away (not all that hard to do,
but you must do it).

Or you can build with honeycomb core. It's bullet proof and fool
proof,
almost. You can pre-fiberglass honeycomb core while it's still
flat, on top of visqueen covered saw horses, and then treat it
like plywood.

The encapsulation is the problem. Once water gets in, and it will, it
can't get out. The best way to handle plywood in my opinion is with
paint which is more easily repaired, and allows for some breathing. I
have some plywood boats over a decade old that are fine. One in
particular, a Payson Skimmer has a glass sheathing on the bottom, but
the inside of the ply is paint. I know that about a hundred folks will
come in and slam me here, like every other time I say eposy is not
waterproof in practice, even if it is in theory so I will not argue. I
have built over 60 plywood boats in my life...

wrote:
On Oct 27, 11:35 am, salmobytes wrote:
..........and even then I was talking about hulls
made with plywood that is skinned on *both* sides
with fiberglass. Hull that have fiberglass on the outside
and a paint or oil finish inside can more easily dry out.

I've seen driftboats--with 'encapsulated' epoxy fiberglass bottoms--so
saturated with water their weight was almost double. If you do
build that way you have to keep up with the repairs, adn patch
dinged fiberglass almost right away (not all that hard to do,
but you must do it).

Or you can build with honeycomb core. It's bullet proof and fool
proof,
almost. You can pre-fiberglass honeycomb core while it's still
flat, on top of visqueen covered saw horses, and then treat it
like plywood.

The encapsulation is the problem. Once water gets in, and it will, it
can't get out. The best way to handle plywood in my opinion is with
paint which is more easily repaired, and allows for some breathing. I
have some plywood boats over a decade old that are fine. One in
particular, a Payson Skimmer has a glass sheathing on the bottom, but
the inside of the ply is paint. I know that about a hundred folks will
come in and slam me here, like every other time I say epoxy is not
waterproof in practice, even if it is in theory so I will not argue. I
have built over 60 plywood boats in my life...

Anybody that comes along to slam you will have to explain himself real
well. I repair these problems all the time and even replace plywood
deck core with the edges only partly taped down - SO THE MOISTURE CAN
GET BACK OUT - Sorry - I guess I'm too used to shouting that at people.
If it is a very highly stressed area, like under winches and
stantions, sometimes I glass that area and then pull tape to the edges
to make the structural beam.
Matt Colie