How waterproof is marine plywood ?

[Russ Turpin]

-*--------
Imagine the compartment under a V-berth, whose rear bulkhead is a sheet
of marine plywood tabbed to the hull. Is it possible to turn this into
a collision compartment by fitting a waterproof lid to this?

This question is really about marine plywood, rather than about a
V-berth bulkhead specifically. Is a vertical bulkhead of marine
plywood an adequate floodwall? (Assuming, of course that all its
joints are tight.) How many days would the plywood last, with water
fully flooded on one side? Regular plywood fairly quickly soaks
through and loses structural integrity if exposed to standing water,
but marine plywood is distinguished by the use of waterproof glue.
Still .. it is just plywood.

Russell

--
This new ship here is fitted according to the reported increase of knowledge
among mankind. Namely, she is cumbered end to end, with bells and trumpets
and clock and wires, ... she can call voices out of the air of the waters to
con the ship while her crew sleep. But sleep Thou lightly. It has not yet
been told to me that the Sea has ceased to be the Sea. -- Rudyard Kipling

[fish...@my-dejanews.com]

In article <6o0p5t$f3l$1...@news.kodak.com>,

tur...@temporarily.unavailable (Russ Turpin) wrote:
> -*--------
> Imagine the compartment under a V-berth, whose rear bulkhead is a sheet
> of marine plywood tabbed to the hull. Is it possible to turn this into
> a collision compartment by fitting a waterproof lid to this?
>
> This question is really about marine plywood, rather than about a
> V-berth bulkhead specifically. Is a vertical bulkhead of marine
> plywood an adequate floodwall? (Assuming, of course that all its
> joints are tight.) How many days would the plywood last, with water
> fully flooded on one side? Regular plywood fairly quickly soaks
> through and loses structural integrity if exposed to standing water,
> but marine plywood is distinguished by the use of waterproof glue.
> Still .. it is just plywood.
>
> Russell
>

How long do you want it to last ?

My guess based on my 30 years experience (and with a couple of caveats - see
below) would be "for years".
After all, there are enough plywood boats around, and they're not all trailer
sailed. A fair number live on moorings.

The caveats: 1. The bulkhead is stong enough to withstand the water pressure
2. You paint or otherwise protect the surface - the glue may be waterproof,
but the veneers are well just wood, and sooner or later they will rot

basically, the unprotected wood will give out before the glue will; but even
so you're not talking days, you're talking months.

S Fishwick

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[macnaughton.com]

If the structure is strong enough to hold the water in the first place it
should last indefinately. Remember there are plenty of plywood boats out
there.

Tom MacNaughton
http://www.macnaughtongroup.com

Russ Turpin wrote in message <6o0p5t$f3l$1...@news.kodak.com>...

>-*--------
>Imagine the compartment under a V-berth, whose rear bulkhead is a sheet
>of marine plywood tabbed to the hull. Is it possible to turn this into
>a collision compartment by fitting a waterproof lid to this?
>
>This question is really about marine plywood, rather than about a
>V-berth bulkhead specifically. Is a vertical bulkhead of marine
>plywood an adequate floodwall? (Assuming, of course that all its
>joints are tight.) How many days would the plywood last, with water
>fully flooded on one side? Regular plywood fairly quickly soaks
>through and loses structural integrity if exposed to standing water,
>but marine plywood is distinguished by the use of waterproof glue.
>Still .. it is just plywood.
>
>Russell
>
>

[Russ Turpin]

-*-------

> How long do you want it to last?

"Hours" is good. "Days" is plenty long. The purpose of a collision
compartment is to prevent the boat from sinking if you run into the
fabled whale or cargo container. A medium-sized hole can sink a small
yacht in minutes. In this rare event, the difference between minutes
and hours can be all the difference in the world. In hours, you can
rig a patch, pump out the water, and figure out what you want to do in
the longer term. If all you have is minutes, things are hairy.

> You paint or otherwise protect the surface ..

Good point. What kind of paint? (Of course, the wood won't rot in
hours, or even days, but even so, it should be protected.)

[Mel Haylock]

Russ,
Marine plywood is not waterproof -the glue holding it together is. Untreated
marine ply would absorb water (a little slower because of the tighter-grain woods
used). After a few wet/dry cycles untreated marine ply would tend to weaken and
warp. If you can seal the sufaces of the wood (especially the edges) it will last
a long time.

Mel Haylock