Leak repair - Gluvit, 3M5200, G/Flex 650

I need replies from those with experience sealing leaks in riveted aluminum 20' boat. My 20' SeaNymph Great Lakes Special sits on a hoist behind our house until I motor out 2 miles at 25mph on Lake Michigan for solo salmon fishing twice a week May-Sept. It winters on a trailer, then I haul it 1/2 mile in Spring and Fall to/from its winter home. Until late 2023, it didn't leak but 1+ qt per 5 hours. With an automatic bilge pump, I was not very aware of leaking. Fall 2023, leaks appeared (2-4 gallons/hr) after a 15 mile trailer ride, and the local marina patched some rivets, seams, and old screw holes in the transom. They used either 3M 4200 or 5200. Again, it was leak free....until Fall 2024 when ti started leaking 2-4 gallons/hr after another 15 mile trek to the marina for motor work. The marina said many bottom rivets were dripping water when they took the boat out of the water after testing the engine work. Come Spring, I need to repair the leaks. I love that boat for big water fishing (heavy aluminum, high freeboard, deep V), and I'm too old (80) to buy another boat+motor. Only a few more years of solo salmon fishing are in me. So, it's try to stop the leaks. I need to hear from those who've used Gluvit, or 3M-5200, or G/Flex650, or Loctite to repair rivet and seam leaks on a big boat that goes 25mph to deep water, then trolls for 5 hours at 2.2mph, then returns home at 25mph, frequently in 2-3' swells. Two problems: 1) Turning the 1,500lb boat over is nearly out of the question. Turning the boat over would involve emptying the 20 gallon gas tank, and removing the 100hp motor. So I need to seal leaks while laying on my back under the boat, from the outside. 2) I replaced the flooring 10 years ago. Between the floor and hull is sprayed in closed cell foam, so the rivets and seams below the waterline are only accessible from the exterior.

PS: Don't just suggest I get a bigger automatic bilge pump. That drains the battery and my kicker doesn't charge the battery, and I'm not going to idle the 100hp for 5 hrs just to keep the batteries charged.

So, which product is best for my application without turning the boat over: Gluvit, 3M 5200, G/Flex 650, or Loctite?. No fast-cure needed. Please give me your opinions based on experience.

It’s likely the rivets at the center chine that are suspect. However, the ideal repair doesn’t sound like a viable option for you, i.e., turning it over, removing the floor, etc., then weeping in G-Flex 650 and then rebucking all the rivets.

That said, I’d clean it all up the best you can, if any areas stripped down to bare, then I’d acid etch them by washing w/ a copper sponge soaked in white vinegar and as soon as bone dry, prime those areas.

But I’d likely work only ONE side at a time, by TIPPING the boat up on its side, as high as you can (well supported!), to then use a hair dryer to weep the G-Flex 650 into the center chine seam and around the rivets.

Here’s one post with info, read from the 1st post = https://www.tinboats.net/threads/valco-jon-boat-seam-repair.50943/#post-504829

While there are many epoxy choices, I like the G-Flex as 1st - it is a FLEXIBLE epoxy, and 2nd - The 2-part kit is ~$22.

And while this might be controversial, (to some … ), once those repairs above are done, I’d spray the sh#t out if those areas with Flex-Seal, no kidding. Many ‘light’ coats best, follow the recoating instructions to the letter! FWIW a buddy does that to his saltwater tin that use to leak like a sieve, and while not permanent … it had stayed dry and leak free for the season (May to Sept) whilst immersed 24/7 in the salt … surprise, surprise, and much to MY surprise, so there. And he didn’t do ANY epoxy treatment.

Off-Topic, but I’d almost bet $$$ that your hoist system (lack of support, stressing it different ways than while supported on a bunk trailer, etc.), might also be exacerbating or adding to your leaks … so please make sure that the hull is properly supported and positioned. Hopefully it is not a ‘U’-strap hoist system, as those KILL tin boats, stressing them in a manner far outside their design principles.

Here's info on a center keel repair ... once done and done right, ZERO leaks since done, on a tin boat used in the salt to boot: https://www.tinboats.net/threads/center-keel-removal-repair-–-on-a-saltwater-tin.48157/

I've found that the best way of removing several layers is to liberally apply a coat of paint stripper which consists of methylene chloride, then immediately cover it with a thin plastic sheet, like gladwrap. This stops the evaporation of the chemical. Do it in sections. A messy job indeed!

DaleH said:

Here's info on a center keel repair ... once done and done right, ZERO leaks since done, on a tin boat used in the salt to boot: https://www.tinboats.net/threads/center-keel-removal-repair-–-on-a-saltwater-tin.48157/

Click to expand...

Thank you for all the information. Given that the boat is currently being wintered outside and covered, this will be a Spring (May-June) job. I'm collecting information so I have a plan on how to proceed. De-bunking rivets is out of the questions, so any repairs will need to be done from the outside, and preferably with me laying on my back applying whatever, to the leaky rivets and seams. I'm looking for either:

• an annual fix that can be redone each Spring, or
• a 3 or 4-year fix that will last as long as I do for salmon fishing on Lake Michigan.

Regarding the hoist. My bunks run the length of the boat. I made the mistake up until 2023 of having the keel rest (ie bear the boat's weight) on the hoist cross member. Since 2023, the boat is completely supported by the long, covered 2/4's that run under the length of the boat. Resting on the keel for 10 years may have been a major cause of the problem, but the boat is 35 yrs old and kept on a trailer or hoist when not in the water.

Thanks again for all your suggestions. Please keep them coming as I'm gathering information on how to solve what seems to be a straight forward problem.