ToyMan and boat guys - epoxy advice

I'm working on adding a battery mount to my little fiberglass sailboat. It's an open daysailer with a semi-enclosed front cubby. I want to cut out a square and make a box to mount the battery blow the floor of the cubby. The cubby can be seen in this shot - not my boat, but an identical one, even the same color:

I originally looked at ready made hinge open deckplates with drop in tubs, but I don't think I have enough height in the cubby to make one work that's still big enough to fit a group D34M Optima battery in. My plan now is to build a wooden box big enough to hold the battery with a 2-3" lip around it that's open on top, then coat the box in epoxy. I'll cut a hole in the cubby floor and drop it in with the lip acting as a mounting flange on top. I'll make a flat wood lid that will be epoxy coated and will be screw mounted for removability. All wiring will be run inside the hull.

I've never worked with epoxy before, so that's where my questions are. Once I build the box, do I just brush it in a couple coats of marine epoxy? Should I fiberglass tape the corners? Should I screw mount the flange to the boat so the box is removable, or should I just epoxy it in? If I screw mount, I'm thinking a little marine sealant will keep the water out. What kind of paint should I use on top of the epoxy coating to make it match the white of the boat?

Throw me any tips you guys have on epoxy coating wood structures for marine use.

BTW, the box may get wet occasionally when trailering in rain or during a capsize, but the boat is stored in a garage, so I should be avoiding long term water or UV exposure.

Hmmm. I have a little boat project of my own, and I'm planning on covering a few pieces of wood with fiberglass. I'll wait patiently for a few nuggets of wisdom.

Coat it with epoxy. Just brush it on the wood. I would also glue it together with epoxy. Buy disposable chip brushes from HF for applicators. I would also pick up some latex gloves. I can't work with epoxy without getting it on my hands. I would also pick up some epoxy pots. Epoxy won't stick to them so they are reusable. I use wood tongue depressors for mixing sticks.

As far as the rest of the design, I would screw mount it with 3M 5200 for a sealant. You can build a hatch or use one of the waterproof ready made ones. I prefer them. Easy, fairly cheap, water tight, low profile, and look professional. Then you just build the bottom of the box to fit.

I would probably tape the joints of the box for strength, and add cloth to the inside bottom and sides, and outside lid for abrasion resistance.

For paint, I like Brightside by Interlux. They have a bunch of colors and it's very durable. It's not cheap. That will take care of the UV coating. Epoxy doesn't like UV, so make sure you paint it with something. Make doubly sure there is no raw wood anywhere. If the water can get in the wood, all the coating in the world won't save it. If it's well coated, it's waterproof. Getting it wet isn't an issue.

I'll probably read this later and think of something else.

Another thing. Fiberglass cloth will not make a sharp 90 degree bend. All corners, inside and outside will have to have a radius. The bigger the better, but 3/4 is about the minimum for 6 oz cloth. I use a router for outside corners and epoxy fairing compound for the inside corners.

All the hatches I find are hinged, but there's not enough height in the cubby to open a lid for the size box I need. Hence the flat, removable lid. Plus I'm trying to keep expenses down, but if you've seen a removable type hatch for cheap throw me a link.

I figured I'd mount L brackets inside the box and epoxy them in, then overbore a couple holes in the lid and pot them with epoxy so I can drill and countersink flathead stainless screws without exposing pare wood. Same method for the screw mount holes in the flange.

Points taken on glassing the wear surfaces.

Next question - can this be made from MDF instead of plywood since it will be epoxy encapsulated?

Dumb qustion - Could I take the bottom of a standard black plastic battery box, mount a wood flange to it, and cover the whole thing in glass and epoxy for the drop in box? Would the epoxy stick to that?

I'm seeing the word "epoxy" used a lot here, and I've got a gallon of "fiberglass resin" that I'm planning on using. What's the difference?

In reply to 1988RedT2:

"fiberglass resin" is polyester based IIRC. Generally considered an inferior product to modern epoxy, especially for modifications and repairs.

How does fiberglass & Epoxy stick to PVC? Might have another construction idea....

Polyester resin is a very common resin used in most boats. Without a gelcoat or paint covering it will absorb water. Then any wood used as a core will rot. I used polyester resin to rebuild a floor in a boat because it was $16 a gallon instead of $140. 10 years later, all the wood used in that repair is now rotten and the floor needs to be replaced again. I wish I had been able to afford epoxy back then.

Epoxy will probably bond to PVC if the PVC is roughed up with sandpaper. It's going to be a mechanical bond and it probably won't stick very well to slick PVC.

Have any of you guys tried lost foam molding? make a male mold out of styrofoam and then layer cloth and epoxy over it. When cured, dissolve foam with lacquer thinner.

http://www.westsystem.com/ss/the-lost-foam-method-of-composite-fabrication/

I'm thinking maybe I just mold the whole thing out of fiberglass and epoxy it in to the boat permanently then make a flat wood lid.

Would two layers of 10oz woven fiberglass be enough to support 50lbs?

I am curious.. why the need for a battery so big for a boat so small?

Only motor is a trolling motor. Combine my lack of sailing experience with small lakes where the wind dies at the drop of a hat and motoring a long damn way back to the dock isn't uncommon.

ok.. that makes more sense.

Looking at that boat. Why does the box need to be a drop in? you have room in that "cuddy" to mount a box sideways into sides of the cuddy instead of down into the hull. This would allow you to still keep it hinged.

Personally though, when I had both my Sunfish and my GP14.. I never had a motor. I put oar mounts on the GP and would row it back when the wind died.

If my current boat did not weigh over 3000 pounds, I would still consider rowing it.. but that is a bit much, especially against a current.

If you have the money, have you considered a Torqeedo 503??

I am in the process of modding a Torqeedo Cruise R 2.0 into an electric inboard

I have considered mounting it to the side or front but I'll lose a good bit of what little storage is there. The boat is a little larger than a sunfish. I considered oars but there's nowhere good to store them when not in use. Where did you keep yours?

Looked at the Torqueedo. It's bad ass but did I mention I've got less than $1500 in the whole boat and trailer?

Have you looked at OceanVolt's stuff? Talk about cool...

another thought.. cut into the seats and mount the battery. Yes, you will lose some flotation, but not a whole lot. Just remember that small boats need minute weight trimming (your body) to keep them on their "lines" to sail properly.

As for Oars, my GP 14 was wood, so I would store them under the seats

I've seen others do this with smaller batteries, but the main reason to get it forward is weight trim. Currently I run it in a box against the transom. With my weight, the battery, and the motor it's rear heavy even with my first mate manning the jib sheets. Which is why I can't sit more forward.

ultraclyde wrote: Have any of you guys tried lost foam molding? make a male mold out of styrofoam and then layer cloth and epoxy over it. When cured, dissolve foam with lacquer thinner.

Yep, used that method to make a single seat for my Honda 400 motorcycle years ago. Got a big block of Styrofoam and fastened it to a seat pan. Cut and sanded it to the shape I wanted and then glassed over it. Then dissolved out the Styrofoam.

Motorcycle looked like this and I made it so the passenger seat area was filled in and had it blended into the tail and lower seat trim.

Why dissolve out the foam?

In my case because I'm using the inside volume. On the bike.....dunno.

ultraclyde wrote: How does fiberglass & Epoxy stick to PVC? Might have another construction idea....

Polyester resin (the kind sold with most fiberglass kits) won't stick well at all. Epoxy grips tenaciously, especially with a little scuffing on the PVC.

I can't find it right now, but I did a subwoofer enclosure build thread here and I did some tests on it by letting epoxy cure on the PVC and then trying to remove it. Couldn't. A chisel would cut the epoxy, but no matter what I did I couldn't get the epoxy to separate from the PVC. Had to sand it off.

I'll put in a plug for West Systems Epoxy. Super high-end stuff, super easy to work with. www.westsystem.com

Maybe a different route entirely...

I found a -fairly- reasonable removable hatch the right size - Jim Black 11x15

So I'm thinking I get this and then make an aluminum flat stock cage that suspends inside the mount flange. Put a standard plastic battery tray and tie down inside the cage. If the hatch is relatively watertight there's no reason for the interior to actually hold water - it might be better if it didn't. Keep the battery dry and ease wire routing. Any water that does get in can be drained from the hull drain in the stern, plus popping the lid allows air ventilation into the space between the inner and outer hull.

MAd Machine - the other reason I forgot to mount it beneath the floor of the cuddy is to get the weight down low near the keel. This would put it within inches of the actual bottom. I know it's only a foot difference, but every little bit helps for stability.

now if I can only figure out how to build coolers into the forward seats....