Marine Plywood

I have repaired the stringers in my 86 ski nautique. I plan to use handi foam and then use Marine Plywood. My question is how do I seal the marine plywood after I attach it to the repaired stringers. Thanks in advance.

-rob

Sorry Tim but I have to firmly disagree on the treated. Several other have made comments on not using it as well. The chemicals screw up the epoxy bond (even worse with polyester resin)

Rob, Regular exterior ply is made with the same waterproof glues as marine ply is. The difference is, marine because it is commonly used for demanding structural applications has a very high standard for voids in the center plys. Go with exterior. Seal all sides with CPES after making all cuts. Bed the ply down to the tops of the stringers with a thickened epoxy. Use weights to hold it down or screws temporarily. Remove the temporary screws and seal the holes with epoxy. Give the ply another coat of regular epoxy or even better, a layer of glass cloth. Hopefully you have been using epoxy resin. Who's brand?

The only caulking needed would be on through hulls like the cooling water suction strainer. Stick with 3M 5200. It's a marine adhesive sealant with superior adhesion and sealing over any silicones.

CPES

Rob, What do they have for a filler (thickening)? Have you been using any - say for filleting?

Pete, the plywood I used was salt treated. It's now 10 years old and I haven't had any problems with it. I'm pretty sure resin would stick to it with no problem. Before I did it, I talked to an old guy that has worked with boats his whole life. He told me if you were to use untreated wood coated with resin, all it would take is one crack to form to let water in the wood and hold it in, thus rotting the floor. So I went with the treated and coated it with poly.

I'll throw in my .02 on the CPES. It's a pleasure to work with except for a strong odor. It applies easily and has good working time. I put 1 coat on a few scrap pieces and cut them open the next day. The 'soak-in' factor was excellent...it seems to plasticize the outer part of the wood.

Good stuff.

Thanks for clearing up what CPES was. It was a question I was going to ask you fibreglass guys.

The removable rear floor piece in my 89 is trash. I was going to replace it with what we call formply here in Aus it is 16mm thick with a plastic like coating on both sides. This coating would make it fairly water resistant would coat edges with a CPES equivalent.






Pics of formply used to replace floor in older Aus ski boat.

It is a 26" span in the 89 ski. Do you think 16mm (approx 5/8") is thick enough?

Pete, here is the link on the Elmer's fiberglass I have been using. Let me know what you think.

http://www.elmers.com/products/product/product_page.asp?pCode=E770

Let me try to recap everyones advice;

1.)Marine plywood (MP) is good?
2.)Attach MP to repaired stingers with a good thick batch of resin.
3.)Put a layer of glass over the entire floor.

Does this sound like a plan???

robman wrote: Pete, here is the link on the Elmer's fiberglass I have been using. Let me know what you think. http://www.elmers.com/products/product/product_page.asp?pCode=E770 Let me try to recap everyones advice; 1.)Marine plywood (MP) is good? 2.)Attach MP to repaired stingers with a good thick batch of resin. 3.)Put a layer of glass over the entire floor. Does this sound like a plan???

Rob,
1. MP is not needed. go with exterior as stated.
2. yes, use a filler/thickener for high build areas such as fillets or where there may be some gaps like bedding/glueing down the ply to the stringers.
3. A layer of glass over the floor is preffered.

Now, the Elmer's is polyester resin and not epoxy (the reason I couldn't find it!). I would not recommend it. Go with a epoxy such as Mas or West. You can do a search. Greg I'm sure can chime in with a link to U.S. Composites. They will also have the fillers to add to the base resin. West is available at marine supplies. Polyester isn't as strong but the biggest reason I don't recommend it is it is hygroscopic. Not really a good thing around water!!! Boat hulls are made with it because it is less expensive.

Lewy, Interesting project. Keep the pictures coming. I too (like Greg) am skeptical about the board/sheet goods you are describing. If you are going to coat the edges which may not bond to whatever is on the surface creating a potential leak, just go with plywood completely coated.
Also, to make the post narrower and easier to read, go back in and edit your post. By using the "enter/return key between your pictures, it will stack them from top to bottom instead of side to side. Thanks