Cracked ribs in large boat questions

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Apr 8, 2021
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Columbus, Ohio
Wow-the amount of bad advice in this thread is Some of the posters obviously haven’t done a full rebuild or braced a big aluminum hull properly. Or actually welded anything.
I’ve rebuilt several SeaArks over the years, and that year hull used .100” ribs and a .125” keel, which isn’t thick enough for anything over 16’....especially if there’s a lot of weight up front. I won’t get into the physics, but those hulls flexed a lot, especially midship. The hull is fine at .125”, and the gunnels were solid. The newer transoms are aluminum tubing filled with polymer....but the older ones were wood core inside aluminum tubing if I recall?

The ribs on this hull are absolute garbage. Not worth salvaging honestly. They’ve split, cracked, been patched and welded and re-welded, with holes drilled everywhere and rotted pinholes throughout. Junk.

I know you probably don’t have the boat anymore, but I would recommend bracing across the gunnels (to maintain factory specs) and then tearing out the factory ribs. Have a decent fab shop build new ones, .125” minimum, and add a few more while you’re at it. Then flip the boat over and weld a full length ‘C’ profile keel cover over the factory keel. Schedule 40 pipe at least.
Put in the proper decking and/or benches-they add major strength to the hull.
Throw in another pair of stout knee braces (4 total), some 3/16” plate over any transom tubing that has a motor mount going through it, and you’ll have the basics for a solid hull.

Starting to sound like work isn’t it?

For the record, don’t EVER sand or bead blast a hull that you plan on welding. It makes it impossible to lay a bead on. (Ask me how I know...). Also, don’t let water sit in a boat like that, ESPECIALLY if it freezes. That’s a sure fire way to crack every weld in the floor.
As for alloys to use-5000 series are ‘marine grade’ and great for hulls, walls, consoles or floors, 3000 series works fine for floors, walls, consoles etc, and 6000 series is what your structural stuff (tubing) is typically made from. It’s perfectly fine to weld into a hull.

What happened to this hull anyways?

Poormans Boatright

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May 5, 2011
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Texas City, Texas
Been there, done that. Weld up the cracks as best as you can. Then use some 2x2x.250 angle iron all the way across on every rib. Stitch weld it with mig. The wire feed welds over dirty old aluminum better than tig. Plus it's gonna be alot of welding.