[Tigosaurus]

I removed the rotton transom board and discovered a lot of corrosion on a 40 year old boat transom from installed galvanized bolts. I've been recently getting used to my fairly old Lincoln Precision TIG 185, and finally have enjoyed making a few repairs on a couple of leaky old boats that needed repair for years.
Must say I've thoroughly enjoyed doing repairs but after welding and then grinding, I have seen a leak here and there, discovered by holding a flashlight on one side of the transom and viewing. Getting better, but still happens. I've used a copper plate covered with aluminum foil over corrosion and bolt holes since the old aluminum transom metal is a little uneven and was getting some air infiltration. Using ER4043 tig feeder rod
Some photos:

IMG_0338 (1).JPG (55.34 KiB) Viewed 4735 times

IMG_0339 (1).JPG (52.32 KiB) Viewed 4735 times

I have cleaned and welded over a lot of the damage on a different part of the transom, but curious as to what others would do:
1. cut out the severely corroded area and weld in a patch of fresh aluminum? or
2. clean and even partially drill out part of the corroded pits as pictured and weld over?
I found it is very time consuming and costs a lot of Argon to weld over the old corrosion pits, but not sure it is a good idea to cut in an aluminum patch since the patch alloy I purchase will probably different from the boat alloy.
Another question is, are there implications of problems such as later cracking as the boat is pushed on choppy water? Some of the areas I've patched are pretty thick compared to the surround substrate. Will appreciate any constructive criticism, might be next day before I can review, but I appreciate anyone's input.

[exnailpounder]

Some aluminum boats are made with un-weldable alloy. Is there any welding on this boat or all mechanical fasteners? The reason I ask is that you might be better off welding individual holes rather than cutting in a patch if the alloy is un-weldable. Un-weldable alloys are, in fact, weldable but they crack very easy as the weld cools so thats why you might be better off just welding the individual holes closed. Also, I would bet there is plenty of contamination in 40 year old in-service aluminum so welding in a patch might be a nightmare and you have the problem of eroded metal from corrosion. I haven't done any of this type of repair so I am interested to see what others say.

[Rick_H]

I know a guy at work that had similar issues and no luck welding bought a coating made for that type pf repair and did the entire boat. It wasn't cheap but has been in service over 2 years and not a single issue.

[Tigosaurus]

I looked over the boat and there is not a weld on it, thousands of rivets. I have done some welding over some other holes and cratersm even enclosed the enlarged holes but it is not easy. The boat is covered in "Gluvit", so I will stick to overwelding the craters and holes for strength and hope for the best. And probably place an order for a quart of Gluvit.
Thanks for the input!

[soutthpaw]

Zinc soldering rod, often sold under names like Aluma-weld that is applied with propane torch might be an option here... never used it myself. Maybe others have experience

[Jim FLinchbaugh]

Zinc soldering rod, often sold under names like Aluma-weld that is applied with propane torch might be an option here... never used it myself. Maybe others have experience

I've seen a video or 2 showing that stuff in use. its quite the process and requires constant wire brushing as any surface oxide is not allowed. So weld and inch, clean, weld and inch clean and so on. It does seem to have good strength though.

[Tigosaurus]

Never thought I would encounter un-weldable aluminum in boat repair, but I will have to give this a try. Thanks for the tip.

[aeroplain]

It's not unweldable, just a pain in the ass. The corrosion goes deep in the pores and causes all kinds of problems, but I've welded hundreds if not thousands of corrosion holes in boats.

Never thought I would encounter un-weldable aluminum in boat repair, but I will have to give this a try. Thanks for the tip.

Ditch the tinfoil and use just copper clamped to the inside, weld from the outside first. There will be a blob, but after you weld the inside the outside can be made flush. A drill bit of whatever size needed gets the majority of the crud out prior to weld too. Make sure before you put in the new wood that you paint the boat first to create a barrier from further electrolysis. I coat the wood as well with a good deck stain that is rated at 15- 25 years. The reason is the trace metals in the wood and glues raise hell. You can use treated wood with this method.

[shipj0]

I know a guy at work that had similar issues and no luck welding bought a coating made for that type pf repair and did the entire boat. It wasn't cheap but has been in service over 2 years and not a single issue.

https://www.flexsealsale.com/flxsl/12.0 ... 87b3b7626d

[cj737]

Most marine aluminum is 5xxx series, so easier to weld with 5xxx rod (and cheaper). I literally just did a transom extension on a Jon boat 2 weeks ago, and encountered some of these issues. You can, plate either side and weld the panel to the transom. You can back either side with copper as suggested and fill the holes, grind smooth. The aluminum is not going to rot now that the galvanized bolts are gone. Use stainless going forward and you should not have any further issues.

The transom is pretty thin, so don't fret too much about the notion of cracks. If you have access to a MIG gun, it works a treat sewing thin aluminum up.

[Tigosaurus]

The boat sat on the driveway for a couple of years while I did other projects. Started back on it, used HTS 735 II braze rod to fix these and other leaking rivets. Easy to use with map gas, stopped the leaks that were "cool cracking" and other leaking rivets. However, I did try tig patching a couple of holes in the floor of the hull with some 6063 aluminum bought at Lowes and using the ER4043 feeder rod. Welds were good, no leaks in the welds themselves. I guess the transom skin was especially deeply contaminated as I have not had any issues since starting on them. Thanks to CJ737 for your advice.

[Poland308]

Good to know you were able to make it work. I’ve recently used the Harris version of the aluminum soldering rod/flux core and had good results with propane and or map gas. Not sure those new aluminum solder options were as good a few years ago as they are now.

[sschefer]

Wish I would have seen this thread sooner. After cleaning up the bad spots use Marine-Tex to fill in the holes and pitting and then coat it from the inside with Gluvit. Here's why: All those riveted seams have Butyl Rubber strips between them. If you melt it, you will be chasing leaks forever. The Aluminum on thin riveted boats is 6061. It can be welded away from seams and with heat sinks to keep the heat away from traveling to the seams. If you have cracks you should use a magnaflux process to find the end of the crack and drill a stop hole.

Is the boat a StarCraft or MonArk by any chance. The thousand rivets statement in your earlier post made me think of the ones that I had fixed in the past.

Hopefully your fixes work just keep an eye on it and make sure your bilge pump is working.