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Tough bottom finish and waterproof hatch questions

Old 01-27-2023, 01:58 PM
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Outrider6
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Default Tough bottom finish and waterproof hatch questions

I plan on building a Dumas Windy, converting to electric power, and adding a tough bottom layer. I won't commonly run over dry ground, but it will skim over rough wet stuff occasionally, as most airboats would.

Would you recommend fiberglass or Kevlar for the bottom? I plan to use thin fiberglass cloth above the waterline, with finishing resin, then paint. Thicker or a double layer on the bottom?

And, are there any extremely abrasion-resistant (tough) 2-part epoxy paints to put over that 'glass or Kevlar cloth and cured resin? Particularly ones that can be brushed. I am capable of spraying, but I am not spraying epoxy in my basement and even though this is the SE USA, it is winter, and days above 60 outside are not common.

Finally, especially since I am going electric and want to eliminate any switches through the hull, I plan on incorporating a small drybox into the hole where the deck cover would be attached with screws or tape. I do NOT want to fiddle with that screws or tape frequently. Imagine a 4" x 6" x 2" Otterbox sticking down into that same perimeter hole in the deck, with the hinged and gasketed lit exposed. I would much rather just pop 2 lid latches and open it up to do stuff like connect the battery. Of course, a huge hole (most of the entire bottom) would be cut into the drybox, while the outer perimeter of it was sealed around the deck. It would stick up enough from the deck to expose the lid latches. I feel confident that would keep out all spray and wash. Almost, if not completely submersible. And big enough to stick a few fingers down into the hull to do stuff.

Thoughts on all of this?
Old 01-28-2023, 07:28 PM
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Don't bother with finishing resin. You can glass it if you want, but finishing resin is a waste of time/money/weight. Go straight to primer.

You can make hatch locks mostly waterproof, but for a big hatch, you'll want to use one at each corner.
Old 01-29-2023, 05:53 AM
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Originally Posted by JS440
Don't bother with finishing resin. You can glass it if you want, but finishing resin is a waste of time/money/weight. Go straight to primer.

You can make hatch locks mostly waterproof, but for a big hatch, you'll want to use one at each corner.
Are you saying to 'glass it if I want, but to use only primer to attach the 'glass to the wood? I have never heard of doing that. Or are you saying to just put primer on bare wood and count on that alone to protect the bottom from abrasion?
Old 01-29-2023, 07:25 AM
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I thought you meant you were going to use fiberglass (with resin), and then coat with finishing resin. Apparently you meant you were going to use fiberglass WITH finishing resin to wet it out.

Use regular general purpose polyester or epoxy resin with the glass, not finishing resin.
Old 01-29-2023, 08:40 AM
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I would use the West System epoxy which could be mixed with the appropriate hardener to adjust the cure time. Nice thing with this epoxy you can use it as an adhesive as well. For boat paint I have found Klass Kote to be the most durable of paints. After all it is used to refinish bathtubs.

As for waterproof boxes I have simply used Tupperware containers. The lids are waterproof, and you can cut small holes and use grommets or seal the holes and wires with silicone.
Old 01-29-2023, 08:42 AM
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Originally Posted by JS440
I thought you meant you were going to use fiberglass (with resin), and then coat with finishing resin. Apparently you meant you were going to use fiberglass WITH finishing resin to wet it out.

Use regular general purpose polyester or epoxy resin with the glass, not finishing resin.
Aha - I wasn't clear in my OP. That is what I meant - to coat the wood with finishing resin, laying fiberglass cloth, then add a wet coat of same finishing resin, for all of it to cure at once. Then once that is cured and sanded, adding a really tough 2-part finishing paint for color. I was asking if fiberglass or Kevlar would be better for the cloth, and for recommendations for the finish paint (for color) that would be really tough and abrasion resistant.

Did you mean to use general purpose resin instead of finishing resin because it is tougher and more flexible that finishing resin?

Also, I am only asking about the bottom. I'm all squared away about what to use above the waterline.

I'm just looking for recommendations from personal experience what is best to use on the bottom of a wood airboat, to be tough and hold up to abrasion, as it will occasionally skid over rocks in shallow water and slide up onto the shore when done running.
Old 01-29-2023, 08:48 AM
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Originally Posted by Propworn
I would use the West System epoxy which could be mixed with the appropriate hardener to adjust the cure time. Nice thing with this epoxy you can use it as an adhesive as well. For boat paint I have found Klass Kote to be the most durable of paints. After all it is used to refinish bathtubs.

As for waterproof boxes I have simply used Tupperware containers. The lids are waterproof, and you can cut small holes and use grommets or seal the holes and wires with silicone.
Thanks for the brand recommendations. I have thought about using Tuppeware, but kind of dismissed the idea because some of the lids require a good bit of force to pry open (with cold fingertips and it may be wet). Now I will try to find something in the size I need and test how easy it is to open the lid. That gives me another option.
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Old 01-29-2023, 11:28 PM
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Prop and I don't agree often but, in this case, he's given good advice.
West Systems is made for use in a marine environment and is what I use to build sport and scale hydroplanes. If you mix the 105 resin, 106(fast) or 109(slow) hardeners and 423 graphite powder, you will have a low friction abrasion resistant surface. With that said, I've never used FG cloth on any wood boat I've built since, using aircraft grade plywood, it just isn't needed. Here's a link to the graphite powder, if you're interested:
423 Graphite Powder | West Marine

Last edited by Hydro Junkie; 01-29-2023 at 11:39 PM.
Old 02-01-2023, 04:00 PM
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If you actually plan to be bouncing off of hard things, a layer of fiberglass is definitely a good idea. Not necessary for a "regular" RC boat, but for things like airboats and jet boats that run in shallow water and are likely to encounter "obstacles", it certainly won't hurt. Fiberglass should be sufficient, no need to go kevlar. Kevlar is also a bit more difficult to work with, although for a fairly flat area like the bottom of an airboat it shouldn't be too bad.

Again though, skip the finishing resin and use general purpose. West Systems is good stuff, I prefer System Three myself. You would also be completely fine going with a chopped mat and polyester resin, which would make sanding and filling for paint easier. Not to mention a bit cheaper. Just remember, you can't use chopped mat with epoxy!

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