Rot Doctor


Subject: Replacing Front Deck on Small Fishing Boat
Date: Mon, 07 Dec 1998

Dr. Rot:

I am in the process of fixing up a small 14 foot 1983 fiberglass fishing boat that I got a pretty good deal on (boat, 25hp Merc outboard and galvanized trailer for $500). Everything works, but need some repair. I found your website while searching for the proper way to replace a small front fishing platform, from which the seat post socket has ripped out due to the wood rotting under the thin fiberglass cover. Here are some pictures of what I am talking about (front bow picture is FYI, no damage there):

This front fishing deck appears to have a piece of partially rotted 1/2″ plywood under green fiberglass on top of floatation, but this wood does not seem to span the entire front deck for some reason, from what I can tell. As you can see from the numerous holes, the previous owner has already tried to re-orient the seat pedestal socket and drill new holes, but failed probably due to the rotted wood and lack of wood not holding his screws. My gut feel is that we need new wood somehow to fasten the seat post socket into.

Please understand I am not a shipwright; I am just a guy with a cheap boat trying to fix it so that I have a decent second boat to fish in quiet coves with. However, I am pretty decent with my hands and have a decent set of power tools. My proposed solution is to cut out a piece of 3/4″ thick exterior grade plywood that matches the contours of the front fishing deck, suitably seal it from moisture (this is where your products come in, namely CPES), and then either paint it with a good hard abrasion resistant finish or place some outdoor carpet over it. I would bridge the gaps between the new wood and the fiberglass hull with fiberglass tape and resin. Here is a picture of the actual wooden plywood piece I have cut out for this purpose as well as how I would affix it:

This new wooden surface would be affixed to the original green fiberglass deck by driving 1 1/2″ brass or stainless steel wood screws where you see the red X markings.

I would not use wood screws here. You won’t get a good grip on fiberglas. I would recommend stainless anchor bolts or molys. They will give you a good hold on the underside of the old glass deck.

I planned on using a waterproof construction adhesive known as Liquid Nails between the epoxy treated new plywood and the original green fiberglass deck to reinforce the grip between the two.

Think about and maybe test with the Liquid Nails before committing. My experience is that Liquid Nails tends to “skin over” fairly quickly. The LN may work… just be sure. There are a bunch of waterproof adhesives out there in gallon cans that might be easier to work with and with slower set times.

Dr. Rot, you seem like someone who has been around boats for a long time and understand the right and wrong way to do things. The local boating supply stores (West Marine, Boat US, etc) tell me almost by reflex that I need to rip everything out of the deck, replace all the rotted wood and rebuild with new marine grade plywood. You probably can also understand that I am looking for a practical solution for this used boat, which will be protected from the elements at all times and rarely, if ever, subject to water on the front fishing deck again. Please comment on:

- your thoughts regarding possible solutions to this problem, and whether or not you think my solution has merit and is workable. I am open to suggestions, all I have done is cut some wood thus far. I would fully appreciate any advice you would care to give me.

Sure, you solution is workable. What you are doing is just rebuilding over the old and saving yourself the trouble of all the tear-out. For an old boat I’d do the same.

- Is fiberglass tape and resin good for sealing the gap between hull and new plywood on the edges? Is Liquid Nails Heavy Duty Construction Adhesive (the sub-flooring variety) the right type of adhesive to use here? It says it is waterproof, for exterior use and strong. Maybe a marine polyurethane would be better, or some type of epoxy adhesive?

Yep, your glass and tape will work. Just rough up the hull a bit for good grip. I am assuming that the new wood would just sit upon the old structure, and that there is enough strength left to support the new platform. If not, you’ll have to think about support strips bonded to the hull for strength. See my note above on the Liquid Nails.

- Is CPES the right product to use to seal the new plywood against moisture intrusion in the future? This piece of wood is 30″ x 48″, I’m thinking the 2 pint kit might be the ticket. What do you think, will this be enough?

Yes, CPES is the right product to protect the new wood. You will need to pay special attention to the new ply edges, applying as much CPES as the wood will accept, and you might be surprised how much that is in some places. I would give the edges 2 coats, and probably the surface as well. The second coat absorption will be much less. It’s the edges on the ply where the rot problems are most likely to start. I would recommend that you buy the 2-quart unit. Two pints might not do it, especially with all the edges. Obviously, you do the CPES application BEFORE the glass/tape installation.

- Do you know of a good paint (maybe epoxy?) that would stick to the CPES treated plywood and stand up to abrasion (remember, people will be standing on this plywood fishing)? Is the outdoor carpet a better idea CPES? How many coats do you recommend?

No, you need to use the CPES. The CPES protects the wood, the carpet only covers it. If it were me, I’d apply 2 or 3 coats of a polyurethane paint over the CPES covered wood, and then put carpet on top for abrasion protection and traction.

- Do you agree with the local boat supply houses? Should I rip out the old decking, the floatation foam and replace everything with new marine grade plywood? The green fiberglass looks like it is bonded to the hull with some sort of adhesive, and will probably be a bear to rip out. Might not be able to get it out without cracking it, it appears old and brittle. However, if it the only right answer here I am willing to listen.

Well, ripping and replacing “as new” is the easy answer. In the real world it’s a lot more work. If you can accommodate the higher platform and the slightly greater weight of the added material, then your way is a lot easier and cheaper.

Thank you for reading this email. I know you are not in the business of giving out free advice on how to repair boats, but I was hoping perhaps you could take a moment to steer a potential new customer in the right direction.

Thanks again for your advice,



What you plan to do is exactly the solution I would have come up with under similar circumstances — assuming the height/weight changes are acceptable. Just be sure to do a good job with the glass/tape to give strength. I would also consider drilling and infusing the old rotten wood with CPES to give it enough body and strength to stand the weight of the new decking. You’ll have to think about this, because it would mean buying about twice as much CPES.

Come back if you have more questions. we’re glad to help if we can.