Non C-dory technical Hull (Driftboat) /non-water liquid test

[Wood Zeppelin]

I apologize in advance, this isn't a C-dory question. But I'm not part of any boating community better and more helpful than this one!

I have a classic wooden drift boat (see pics), with fiberglass over the wood hull. I installed UHMW "skid plate" kit on the bottom to protect from rocks when going down rivers. It's a fairly common modification. It's screwed into the bottom of the boat, the screws aligned with the the inner frame ribs, so that the do not poke thru to the inside. However, recently I noticed a leak coming in the boat. Then, water was in the boat overnight and I saw a small puddle on the ground the next morning under the same spot where I previously saw the water leaking in.

Questions:

(1) The outside is covered with fiberglass and the inside with marine paint. Once the wood gets wet I think it will take a long time to dry. I'm worried that the 1/4" marine plywood will rot around the leak point if this is not fixed?

(2) I think one of the screws is "missed" the rib and may be poking through. Or water is getting between the rib and the 1/4" plywood hull material. But according the the kit, screws going into the wood/through the fiberglass outer shell would not leak. I even added sealant (4200 I think) to the threads before screwing them in. So what's leaking then!?

(3) to track the exact location of the leak, I could pour water inside the boat and find the puddle the next morning. However (a) I'd prefer not to the the wood wet again and (b) just like a roof leak in a house, where you see the water is not always the same as the source of the leak. Water could travel in the tiny space between the fiberglass outer shell and the UHMW skid plate. So my question is, could I pour something OTHER THAN WATER that is equally as "runny" (low viscosity) but won't encourage rot? Like denatured alcohol (except it evaporates too fast). I'm leery of solvents that might damage the epoxy-fiberglass layer. What about cleaning solutions? What about water with some bleach in it (would that kill rather than encourage any rot)? Any other suggestions?

[drbridge]

I have built a couple of drift boats and am familiar with different types of drift boat construction. You can find one of them in Roger Fletchers Drift Boats And River Dories, the 16' Rapid Robert. The problem with UHMW bottoms is that it expands and contracts at a much greater rate than the wood. This Will cause the screws to constantly be worked back and forth. There is no sealant that Will adherewto the UHMW. You can expect water to travel through the screws and in to the wood and the boat. Some people love the UHMW because of it's ability to slide over rocks and are willing to put up with the damage it does to the wood. In the case of a bottom that has been covered with fiberglass the water Will soak the wood and be trapped by the glass and promote rot. I would never put UHMW on a glassed bottom. My advice would be to take it off and give it a good long why to dry out and then fill the screw holes with epoxy and put sacrificial coats of epoxy mixed with graphite to protect the glass bottom and help The boat slide over rocks. Good luck

[Wood Zeppelin]

Super Helpful, thanks!

I used to work with UHWM and am aware of some of it's properties, and I do love is anti-abrasion abilities. It's so nice on a drift boat to not have to cringe and worry about future repairs everytime there's a rock. But from what your saying it seems worse to have it on there. I didn't think about the thermal expansion. I imagine the fiberglass expands/contracts very little compared to the UHMW.

Thank you for your suggestion! I think that's what I will do.

[pcg]

[drbridge]

On the boats that I built I put a single layer of 20 oz tiaxial epoxy fiberglass over the plywood bottom and then the coating of graphite epoxy. This is how Ray Heater of Rays River Dories builds his boats and they are renowned for there durability. Not quite as slippery as UHMW but slides over rocks reasonably well. Over time if the epoxy graphite coating wears off you just sand it a little and apply some more. If you're existing bottom is polyester fiberglass the epoxy will stick to it well once you sand it's little. You could also add another layer of glass to it if you don't think it is tough enough.

[starcrafttom]

When I had my alum drift boat I covered the bottom with a pout on product that does the same as the UHMW. boat just slide right over rocks. I would peel the UHMW off and seal all the holes. Then apply glovit or similar product. Just ruff up the bottom and pour it on. takes about two days to cure. You can also use epoxy to glue the UHMW to the hull. I would not drill in to the wood.

[Foggy]

Why not get a qualified marine surveyor's opinion and go from there?

Getting opinions on the internet may not be the best way to protect your
investment.

Granted, much advice given on this blog may be helpful.

Why gamble?

Aye.