Fiberglass over Plywood(new construction)

[rappahanockman]

Hello guys , I'm new to this board and would
like to get some opinions/advice please.
I'm considering having a new boat built to use
for charter fishing.The builders name is
Kinnamon and he is located in Tilghman , Maryland.
His method of construction is fiberglass over
plywood with the fiberglass only on the exterior
surfaces and some type of oil preservative on
the exposed plywood. I'm wondering what kind of
maintenance and precautions I need to take to
keep the wood in the bilge from rotting.

[Ian McColgin]

You don't say how large and whether the boat lives in the water or on a trailor, which makes a huge difference.

A builder might, for cost reasons, not epoxy seal (CPES best) inside surfaces and you may or may not want to order this, especially if the boat lives in the water. The epoxy sealer will prevent checking in the plywood far better than any other product I know. But this builder may well have a marvelous and cost effective approach.

Get the builder to tell you the name of one of his very satisfied customers who has a boat a few years old so you can see for yourself how his approach works.

Epoxy and all marine paints are waterproof in that they keep out fluid but epoxy and many paints are not vapor proof. The moisture content of the wood will go up in a boat that's in the water. Sometimes a surprising amount. We think that my friend's Wianno Sr - old boat amazingly restored by sanding a good bit off the planking and ashcroft layer some cedar, all epoxy set and CPES sealed - gains a remarkable 300# - 400# each season and looses it in the winter. All without damage by the way.

Point being, there will be moisture in the wood, but if it's only vapor the content will not cause the plywood to fail or go gingey. If you've good ventilation in the bilges, she'll be fine.

G'luck

[rappahanockman]

Thanks Ian The boat is 36'x12' and will stay
in the water. It's design is based on the old
Chesapeake Deadrise style workboat. I plan to keep it in a covered slip and I will pay attention to the bilge ventilation as you
suggested.

[RodB]

You should really do some homework. I'm no expert but an epoxy/fiberglass sheath on the outside without a sealed inside is not a balanced structure. (I assume he is not using polyester resin) Is the plywood first rate marine ply? I would think Triple coating the interior with epoxy (glassing even better) would make for a much better (more long lived) hull that would be totally encapsulated. The end grain of plywood absolutely has to be sealed for it to last any time at all...

There are many methods of construction that have worked for years with proper ventilation etc, I would just think that epoxy construction offers better alternatives today. You should definitely talk with Gougeon Brothers for example.

I just offer these comments as an insurance (peace of mind) for a long term investment.

RB

[ 07-13-2004, 12:45 PM: Message edited by: RodB ]

[paul oman]

My two cents would be to use a high solids, solvent based epoxy paint on the inside. This would provide an interior membrane with some degree of flex to handle any expansion etc. of the wood (on the other hand, plywood expands very little).

Even if he uses an oil based stain/sealer inside, it is possible??? that an epoxy might still bond it after a season or two of 'drying out'.

If using a penetrating epoxy (solvent thinned epoxy) make note of the % solvent vs. % epoxy in the product.

hope this helps

paul oman
progressive epoxy polymers

[Venchka]

Find the oldest boat this person has built using the same methods. See what it looks like. How well it has held up.

Wayne

[RonW]

A while back I asked a similar question, basically how to protect the plywood under the floorboards that is unaccessible.Ckeck it out.

http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=008796

I hope thats it. The answer I liked best after doing more research on the subject is Cuprinol.
The green kind that jamestown still sells.
Do a search on this board for bilge protection.