[schindlerweldfab]

A buddy of mine wants me to repair some cracks and holes on the hull of his Aluminum boat. How can I determine what type of Marine Grade Aluminum Alloy it is? I found this list and wasn't sure which one it is? https://metalboatkits.com/guide-marine-grade-aluminum/

[cj737]

Good luck with that...

Every Jon Boat I’ve ever repaired has been a complete nightmare. The absorbed contamination has been extremely difficult to purge out before welding. Currently, my best results have come from a flap disc, then preheat, then Acetone, then stainless brushes, and another Acetone wipe. I use 5356 in my MIG or TIG regardless of the original ally type. It has performed better for me, and I’ve had less heat-cracking as a result.

I use a spoolgun whenever possible for long or large areas to be welded. It allows me to pour enough wire into the hull before a blowout. I TIG it when it’s thick, or delicate. I also run a 25% Helium mix in my Argon tank. For TIG, I run 65% balance, and closer to 80Hz for settings. And I postflow the area to help cool it.

I repaired a buddy’s saltwater trailer last week, and it was the worst job I’ve ever been dealt. Bar none. Two full days to repair 14 bunk risers. Fcuk me!

[schindlerweldfab]

CJ737- Thanks for the response and the incite regarding the nightmare this will be. I think I might just pass on this one, seems like more of a big hassle.

[Poland308]

One of the guys I work with moonlights doing boat and pontoon repairs. He has a 500$ minamum just to clean up the cracks to see if there weldable. Then most times on spots that are spiderwebbed or corroded bad he’ll cut out to clean metal and patch it in.

[noddybrian]

I've done a few boat repairs like this & it's never going to be pretty however you try it in my experience ! I would not try Tig unless it is the only option as you will never get it clean enough & I never had much luck trying - over here we can get thin ( like 0.8mm ) mig wire & that run with a spool gun can be turned down more than people think so burn through is not so bad - my method ( which others will likely disagree with ! ) is clean with sand blast - inside & out of repair area - then if it's a crack / split which is the most common -weld a patch on the inside larger than the damage - if material is super thin try to clamp a chill piece on the outside - make the repair piece thicker than the boat but not excessively so & favor that when welding - having one clean half always helps with porosity - if need be grind off nasty stuff & run another bead over the first - each successive bead will usually improve - then grind the original crack out lightly & weld it from the outside to the patch as though it's a backing bar - this weld can be flatted off if need be prior to painting - if the boat is totally rotten / un-weldable there are epoxy coatings or spray-able mastic systems that can be used depending on how much the owner is willing to pay out - if you have access to a modern inverter Mig with pulse these can work too with just a change of drive roll & liner.

[cj737]

What Noddy mentioned works, but it really depends upon the condition of the boat, the type of water it runs in, and the damage. Looking at the pictures you posted, that boat runs in very brackish water, and it appears to be very alkaline. Those contaminants will embed into the base material. The heavy oxidation areas on the bottom of the hull cause me concern about potential structural instability.

Even to weld patches over those, you’d likely upset the boats handling and cause it to potentially steer off course due to water flowing over them. Cut it out and patch from the inside, that poses other issues. You’d need to cut the hull loose from the stringers and ribbing, then reweld that, if you can gain access. That console has to come out, the fuel tank, and wiring be moved to do that type of repair.

For clarification, I’ve only used TIG when welding transom extensions on where there’s thick plate involved for motor mount brackets. But it’s on the “new” section or when welding a thin patch over a forward hull section (not within the running water line). And that patch area was cleaned extensively inside and out first. It did take a couple of passes to get all the porosity ground away ultimately. Lots of work for little damage for certain.

[Artie F. Emm]

What causes that kind of cracking?

[cj737]

What causes that kind of cracking?

In the hull? Fatigue, impact, stress, corrosion... All depends. any ally boats are under-structured so they flex a lot. Folks overload them, then with thin hulls and stress of pounding on the water, the sheet stress cracks. This is very common with riveted hulls. Riveted hulls often get leaks from the stress/expansion of the hull against the rivets, where the rivet ultimately leaks. Riveted hulls are less expensive, but less durable.

I've repaired quite a few of these hulls, none have ever been fun. I even ground off (exterior side) all the rivets on a buddy's then welded the hull and stitched it from the inside against the ribbing/stringer. Fortunately, it was pretty clean and barren interior. He used it primarily for fresh water pond fishing with his kids. We ultimately built a casting platform (ally angle iron for stringers, 1/8" sheet for the deck) and carpeted it. Made it light, strong, and safe for his kids to fish from. Took about 3 days, but where kids are concerned, no time is too much time to spend for their development in my book.

[kiwi2wheels]

How about using aluminum sandwich patches, top and bottom, secured with closed end blind aluminum rivets ;

https://rivetsinstock.com/rivets/blind- ... ivets.html

and a good one part structural epoxy , similar to Delo Monopox 1196 ? https://www.delo-adhesives.com/us/downloads/

Grind the damaged areas flat, chemically treat the alu to remove the corrosion and provide a good surface for the adhesive to bond to. Use draw clecos to drill / assemble the panels.

Use the steel mandrel rivets and fill the mandrel holes with the epoxy . The other alternative is to use the solid 1100 grade aircraft A rivets.

[pgk]

Those aluminum boat hulls can be a total pain, I remember years ago my brother had one that had a couple of small holes he ended up using some type of low temp rod and a propane torch to patch them seemed to work pretty good, I don't recall what brand or what they were called but the melted in at a much lower temp than regular aluminum rod?? It could have been this stuff: https://www.alumiweld.com/