Difficult Stern/Bottom Repairs?

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Rampaige

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I just pick up this ‘89 Grumman 16. The boat and trailer were free. I’m willing to put some money and effort into getting it back to water tight, but the corners of the stern where the transom meets the bottom are rotted out. They were patched with what looks like maybe 5200 and it’s flaking off. I was beginning to try to clean it up a bit but I noticed the aluminum is in pretty bad shape there. Is this weldable? I can’t imagine there’s another way to fix it apart from finding a welder. Aside from scrapping the hull, what’s the best way to repair it?
 

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It's hard to tell how bad it is. I'd take a stainless-steel wire wheel on a drill or angle grinder and strip it down.
I was able to flake away whatever they used to patch the hole with a screwdriver. I’m kind of impressed with how well that material worked on a hole this size, especially seeing how poorly it was adhered. Will G Flex, JB Weld, etc work for a hole this big?
 

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Strength of the material appears to be gone. If using it as a rowboat or electric power you might get away with a compound patch such as some type of epoxy covering like JB weld. I would never trust the integrity with an outboard motor. If you get it cleaned and patched, I have had great success below the waterline with a product called " leak stopper" from home depot and tractor supply. It is a clear coating designed for roof coatings/ sealer. Just some thoughts here, but trusting that hull with an outboard motor in my opinion would be asking for trouble.
 
I was able to flake away whatever they used to patch the hole with a screwdriver. I’m kind of impressed with how well that material worked on a hole this size, especially seeing how poorly it was adhered. Will G Flex, JB Weld, etc work for a hole this big?
That looks like some new kind of hell.
 
Strength of the material appears to be gone. If using it as a rowboat or electric power you might get away with a compound patch such as some type of epoxy covering like JB weld. I would never trust the integrity with an outboard motor. If you get it cleaned and patched, I have had great success below the waterline with a product called " leak stopper" from home depot and tractor supply. It is a clear coating designed for roof coatings/ sealer. Just some thoughts here, but trusting that hull with an outboard motor in my opinion would be asking for trouble.
Do you think having it welded would be a suitable option? I got an estimate from a welder today for a little over $800 to that corner and the opposite corner which is not nearly as bad.
 
$800 is pretty absurd.

I would find some metal road sign stock and I would heat it and bend it to the needed shape to fit tightly on the inside of the boat. Pop off/grind off the rivets in that area. Apply some sealant and rivet the patch into place.

Then I would rough up the area with a grinder and use aluminum repair epoxy on the outside. I've had very good success with the one made by JB Weld. I think it's similar to their regular JB weld, but it has an aluminum filler instead of steel.

Take your time and get the corners well-secured, and the boat should be okay
 
That rib is going to make things tricky.

If you could get the last inch or so of the rib pounded flat, I would get some 2-3" aluminum flat stock and bend it around that corner as a patch to start with, going a couple inches past the damage on the side and bottom.

I would also incorporate a piece of angle installed from the inside as a backer for further reinforcement, the transom skin looks to be pretty thin. Have your fasteners go through it as well, sandwiching the hull between both pieces. Rivets or stainless nuts and bolts would be fine.

Clean it really well and use some type of aluminum safe sealant between your patches and I think it'll be more than fine.
 
It doesn't have to be super complicated, if you can get the shape right. Here is how I might go about it, depending on what I see in person.

  1. I would vacuum, wipe down and clean the area carefully, maybe using a wire cup brush.
  2. I would gather good aluminum and solid rivets as needed (road sign aluminum is excellent)
  3. I would then use a very sharp wood chisel and/or a grinder with a flap disk and slice the tails off of the existing rivets on the inside, so I could get a nice, surface to work with.
  4. I would then heat my aluminum with a torch and let it air cool to soften and anneal it
  5. Then I would bend/form it into the shape it needed. Maybe something like this, but probably a bit bigger:
corner 2.jpg

6. Once I got a good shape and tight fit, I'd remove the rivets and set in Butyl seam tape
7. Then I would drill and set new solid rivets to secure the area. Add as needed, make it strong!
8. Then I would either MIG the corner shut or use Aluminum repair epoxy to close up the outside

This sounds complicated, but I'm confident I could do it in an hour or two, once I had everything I needed. But even if it takes you an afternoon, I'd be okay with that.

This is one thing that is awesome about boats, whether fiberglass or aluminum. If you aren't scared and learn some basic methods, you can do a LOT in a short period of time.
 
It doesn't have to be super complicated, if you can get the shape right. Here is how I might go about it, depending on what I see in person.

  1. I would vacuum, wipe down and clean the area carefully, maybe using a wire cup brush.
  2. I would gather good aluminum and solid rivets as needed (road sign aluminum is excellent)
  3. I would then use a very sharp wood chisel and/or a grinder with a flap disk and slice the tails off of the existing rivets on the inside, so I could get a nice, surface to work with.
  4. I would then heat my aluminum with a torch and let it air cool to soften and anneal it
  5. Then I would bend/form it into the shape it needed. Maybe something like this, but probably a bit bigger:
View attachment 121728

6. Once I got a good shape and tight fit, I'd remove the rivets and set in Butyl seam tape
7. Then I would drill and set new solid rivets to secure the area. Add as needed, make it strong!
8. Then I would either MIG the corner shut or use Aluminum repair epoxy to close up the outside

This sounds complicated, but I'm confident I could do it in an hour or two, once I had everything I needed. But even if it takes you an afternoon, I'd be okay with that.

This is one thing that is awesome about boats, whether fiberglass or aluminum. If you aren't scared and learn some basic methods, you can do a LOT in a short period of time.
Once annealed will the aluminum be soft enough to conform to that molded chine or will that need to be pounded flat?

Would the aluminum go inside or outside of the hull?
 
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Surprised that heating alum would have any long-lasting effect. Wouldn't you have to work it while it's still red hot?
 
Surprised that heating alum would have any long-lasting effect. Wouldn't you have to work it while it's still red hot?
Not with aluminum. Once it’s annealed, or heated and cooled, it’s more malleable.

…per my research.
 
You may want to research it some more. When you treat steel this way it makes it harder. Been doing this for years when I need an extra hard bolt.
 
It is similar to steel. Heat it up and let it cool slowly and it becomes more malleable. Heat it up and quench or cool it down fast and it becomes much harder but possibly more brittle, depending on the alloy.

Google “anneal aluminum” and you can learn more
 

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