1986 Bow Rider - foam between wood supporting engine mounts and hull

[Tom Z]

I'm new to this site. I bought an older 21 foot Sea Ray Bow Rider to fish Lake Erie last summer. It had a soft spot in the floor at the front of the boat but everything else looked good. I planned to fix the floor at the front over the winter. I've now opened things up and found a bit of a disaster under the floor. The floor and stringers are rotted but the transom looks solid. I removed the flooring, stringers and foam, then the gas tank and engine.
I'm in the process of replacing the motor mounts and stringers. When I removed the existing motor mounts, I found what looks like a 3/4" plywood fastened to a 2x6 PT supporting the motor mounts. the PT was not fastened to the hull. It was sitting on foam. The plywood was rotted and the foam was soaked so there wasn't much left to support the motor. I plan to build a new motor support out of layers of 3/4" marine plywood and glued together and then cover the whole thing with fiberglass resin to make them water proof. I plan to use 3M 5200 to glue the new wooden mounts to the fiberglass hull to make them more solid. It looks like the original install fastened the motor support wood to the stringers on the side and used foam between the motor support and the hull. If I fasten the new motor support wood to the hull, will I cause a problem? I'd appreciate any advise anyone might have to offer. I've attached a picture of the old support. Thanks,

 

[Sundancer]

I'm not sure the plywood would hold the bolts, given that the plywood would be on edge if I have that right. We're tackling a similar project on a 1986 Marlin Ski Boat. The plywood floor was held up by the fiberglass and foam. Digging into it, the plywood looks like bark and is rotten. We'll replace that. The stringers are bad in some areas and worse in others. I'm looking at a product from the Rot Doctor in Seattle. It can be used to stop wood from rotting further and to prevent rot on new wood going on. Then you can pour another product in to fill up the voids and surround the wood to build a new stringer basically out of epoxy using the fiberglass as a mold. Sounds good, but we are still peeling the old stuff out. They say you can just drill a hole every 5 inches or so and start with the rot stopper. After a week or so, you can start pouring in the laying epoxy to build it up. We'll see and I'd like to see or talk to someone that has used that product.

How did you get the foam out of your boat? Did you use acetone or just muscle it out with a shovel or hoe? I'm looking for an easy way to do that!

 

[Bt Doctur]

no motor mount is ever held in place by foam.
a typical stringer for a engine mount connects to the transom, hull, and front bulkhead.These are all glassed up . Post some pics to we can see what was done.

 

[Tom Z]

I'm not sure the plywood would hold the bolts, given that the plywood would be on edge if I have that right. We're tackling a similar project on a 1986 Marlin Ski Boat. The plywood floor was held up by the fiberglass and foam. Digging into it, the plywood looks like bark and is rotten. We'll replace that. The stringers are bad in some areas and worse in others. I'm looking at a product from the Rot Doctor in Seattle. It can be used to stop wood from rotting further and to prevent rot on new wood going on. Then you can pour another product in to fill up the voids and surround the wood to build a new stringer basically out of epoxy using the fiberglass as a mold. Sounds good, but we are still peeling the old stuff out. They say you can just drill a hole every 5 inches or so and start with the rot stopper. After a week or so, you can start pouring in the laying epoxy to build it up. We'll see and I'd like to see or talk to someone that has used that product.

How did you get the foam out of your boat? Did you use acetone or just muscle it out with a shovel or hoe? I'm looking for an easy way to do that!

Tom Z.
I was lucky that the foam all popped off the fiberglass hull with a little prying using a small 2" wide flat pry bar. I'm not sure why it didn't stick to the hull very well but it all came off in large chunks clean to the hull surface. That was a good thing as it made it easier for me. All I need to do now is sand the wax surface off the fiberglass on the hull in the areas where I plan to install the glass for the new stringers. As for the new motor supports, I decided to make them up out of solid pieces of western red cedar (6"x6"x22"). I was able to shape it to match the old mount (including the foam spacer to match to hull contour). I still have 3/4" marine grade plywood stapled to these new mounts (front, back and sides) to match the old stringers but this time there will be no foam between the hull and the motor supports. I oven baked the cedar to dry it out a bit, then coated it with fiberglass resin (I cut with resin with acetone to make it thinner like water so it would soak into the wood better). I'm doing the same with all the marine grade plywood to try and water proof it (the original plywood was not water proofed). I plan to mount the new motor supports to the hull using 3M 5200. I will leave a small spacer (maybe 1/8" thick) between the new mounts and the hull. I'm also using 3M 5200 to glue all the new stringers in. When I removed the old rotten stringers, I kept the original peanut buttered area and just glued the new stringers into the same place. I did sand and clean these areas with acetone so I'm expecting to get a good bond. BTW, when I installed the new stringers and floor, I dry fit everything, then removed it to coat with the thinned out fiberglass resin, then reinstalled everything and applied the glass to hold things in place. I used unwaxed resin on everything except the final coat so I didn't need to sand the wax off between coats.

Just a short comment on your chasing rot. I was thinking the same thing. However, every time I opened up an area, I found more mush. I don't think I could have injected epoxy into the stringer areas as the rotten wood would have occupied the space and prevented it. The only option was to completely remove everything and start new.

 

[Tom Z]

no motor mount is ever held in place by foam.
a typical stringer for a engine mount connects to the transom, hull, and front bulkhead.These are all glassed up . Post some pics to we can see what was done.

Tom Z
Motor mount supports should not be connected to the hull via foam but it clearly was in my case (see pic). I'm not sure if this was done in the factory or by someone else who did a shoddy rebuild. I also noticed that the side stringers were not connected to the hull at all. They were tight under the floor but they were a good 3" off the hull and sitting on foam.
The old stringers around the motor do connect to the transom but only at the very bottom as the floor tapers off at the back down to the transom at a pretty steep angle (see pics).
I've also included a few other pics of things that I found.
If I had have know the degree of rot, I would not have bought the boat.
That said, I'm into it now so I may as well do it right.