Klamath hull corrosion


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Sep 21, 2020
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Hi folks!

Just picked up my first boat that I don't have to paddle (at least, I hope to not have to paddle this one). Free from a family friend. It's a 1990 Klamath 14 DLX. It's a welded tin boat. Came with a 1985 Mercury 25 XD outboard. Neither boat nor outboard have been used in nearly 20 years. The outboard at least was stored inside and it looks like somebody had the sense to winterize it before putting it away -- it will probably run pretty good with a little rehab. The EZ Loader trailer is rusty, had no working wiring or lights, had an old frayed poly rope on the rusted winch, original rubber on the tires, probably original grease in the bearings. Redid the trailer wiring, added lights, replaced the winch and strap, new tires, repacked the bearings...didn't do much about the rust.

The hull on the boat looked in OK shape. I vacuumed out about 10 gallons of dirt and pine needles out of the bottom, attached a triangle of plywood to the bow with self tapping screws, mounted a bow-mount trolling motor to that and took her out to the reservoir to see if she floats. The good news is that she handled great even considering the rain and gusty winds and with only an electric trolling motor for propulsion. The less good news is that she wouldn't float forever -- after 3-4 hours on the water there was maybe 10 gallons of water in the bottom of the boat. It was drizzling, but that seemed to be too much to just be attributed to rain.

I went exploring with the boat back on the trailer and found a few patches of corrosion at the bottom of some ribs on either side underneath the middle bench seat, looked like little spots of crumbly grey graham cracker. Barely looked like much of anything. Then I probed them with a needle and found a couple have holes (from pinhole to 1/8") that go clean through the hull. Of course, even the spots that don't have holes yet are probably pretty compromised.

I drilled out the rivets and removed the bench seat top revealing some ancient moldy wet foam and a bunch of mouse nests at the bottom over the leaks. I'm not sure why Klamath thought it was a good idea to make an otherwise inaccessable area under the seat have a drainage opening that would fit a mouse. I assume the combination of constant moisture and mouse pee made a witches brew that caused corrosion at the bottom of some of the ribs where water pooled. What's the best way to fix this in a cost effective way?

Bench seat and foam removed. Gross. The corrosion is mostly below the debris.
Spot of corrosion from below, with pinhole causing leak.
Several spots of corrosion from below, 2 mm hole causing leak.
Some of the offending moldy wet foam.
Being a budget minded fella myself, I would clean that hull inside and out within an inch of its life. Then use a nyalox wheel on a drill to clean the suspect areas. If there are only a few, I'd patch it with JB Weld. I've had good luck with the steelstik, it's the kind you knead together with your fingers and mash into place. Once it's hardened, you can sand it so it's not so obtrusive. First you have to clean down to good bare aluminum or it will come off as corrosion takes place underneath.
A corroded boat is probably not a forever boat, but hopefully you can get a good number of years of service from it.

Sent from my CLT-L04 using Tapatalk

Clean well, wash w/ copper scrub pad & white vinegar to etch the tin, let dry & prime w/ zinc chromate primer, then epoxy. Another epoxy option is the flexible West Systems G-Flex 650, enough to do all (or most) the rivets on a hull for a $20-22 kit. I put links to many DIY tutorials up here about it, fixing leaks & serious/major cracks.

Still ... a simple enough DIY fix for you to do!

And yes, the mouse pee and always being wet’ caused the corrosion. Akin to non-passivated 316L stainless steels, tin needs the layer of air surrounding it to protect itself - which is why you see cleaned tin turn chalky gray - that is the oxide layer trying to protect thyself.
Thanks guys. The rest of the hull is in very good condition, so I'm glad there are ways to patch this.

I'm a little confused about prep:

If the goal is to remove all the major corrosion before epoxy, I'm going to turn some of these pinholes into dime-sized holes, and I'm going to turn several areas that are not currently holes at all into holes. I probably need to use a drill or step bit to ream out the rotten material surrounding each pinhole. Is that what you had in mind, or too aggressive?

I assume when we're talking about priming, you mean from both top and bottom, and just surrounding the defects rather than the entire hull?
CORROSION - Just remove all traces of corrosion or else some types (precipitate corrosion) can continue to exist, as it is self-propagating. See the 16' Starcraft - for gross examples thereof - where I had to completely replace the outside and inside tin skins. That WS 650 info I've posted shows how to fill holes and Johnny has posted many articles here on hole fixing, using pieces of tin can cut to shape.

PRIME - I'd only prime where you repair, if not broke, don't fix it :wink:
Just wanted to update this thread in case it helps anybody. I did fix the corroded areas under the front and middle seats in the hull last year. The boat still leaks a little from under the rear seat which I haven't got to yet but the leaks are now a minor nuisance (a gallon or so over the day) instead of a safety issue so I went fishing instead.

Short version, I coarse sanded the problem areas (both inside and outside) and cleaned with acetone. Duct tape on the bottom of the hull to prevent the epoxy from running out the holes, then from the interior applied West Systems G/flex 650 epoxy and wetted out bits of cheap 2" fiberglass tape and laid it in each area followed by more epoxy. It worked perfectly, I've ran the boat pretty hard since then and no issues. I'm not sure that the fiberglass was necessary but I figured it certainly wouldn't hurt.

My surface prep was far from perfect (several areas has limited access). I probably didn't get all the oxidized metal out before epoxying. Temperatures were way too cold for effective epoxy work and I ended up having to use a heat gun to keep the epoxy workable and then to get it to set up so I doubt it reached full rated strength. Didn't matter, still worked.

To finalize the repairs this year will be similar treatment to the remaining areas under the rear seat, then a coat of 2-part epoxy paint (Wetlander or similar) of everything below the waterline from the outside and I'm pretty sure that the boat will be dryer than a popcorn fart on the inside and good to go for another 30 years.

Thanks for the help!
lka said:
Just wanted to update this thread in case it helps anybody.

... I'm pretty sure that the boat will be dryer than a popcorn fart on the inside and good to go for another 30 years ...
Thanks ... uhhhhh, maybe ... not sure with that testimonial :shock: !

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