Yours isn't the first I've seen with every single rib popped like that. I used to like them - the design, on paper, is superior to many others.
For example, the lateral stiffeners welded (well, not anymore) across the floor are flat on top, whereas many companies use a 1.5" tall hat section that follows the deadrise of the hull. Not only does this give a flat deck, it also make the middle of the stiffener twice as tall as the ends, putting more strength where the greater stress is. Also, the additional lengthwise strakes formed into the hull increase rigidity, without a huge weight gain. Some great design features. But then, the boats just fall apart due to poor welding (and I think they keep making their lateral ribs thinner), and with more of their recent hulls, I'm seeing things that were improperly cut, and then hammered into place. I did a deck extension on one, and found the back of the bow deck was C shaped, when looking down from the top....
The two places I see damage on yours are the disconnected lower floor ribs, and the transom knee brace.
The lower ribs simply need to be rewelded. The splitting of the weld shows how poor the weld was - aluminum welds tend to fail in the heat affected zone immediately on either side of the weld - not the weld itself. The fact that the weld itself let go suggests that the cross section of the weld wasn't even as thick as the base material, when they should have been roughly equal.
I'm going to outline a plan of correctly repairing it. If you are going to spend 500-800 to get it rewelded to sell it, you may also want to consider spending slightly more to make it right enough to keep it. Depends on if the decision is entirely dollars and cents, or if there is also some 'new boat itch' to contend with as well.
My initial thought is to simply get these properly rewelded. This is not a TIG job - you'll end up with quite a bit of distortion - it's really a task for pulsed MIG. I'd advise not leaving it with someone who plans to TIG weld that.
However, the more I look at your pictures, the more I'm concerned that the fitment is too far off to work with. I'm somewhat surprised that the ribs lifted up from the hull sheets as much as they did. With the weight of the boat on the trailer bunks, I'd really expect to see the gap closed up, so this suggests a good bit of internal tension that is pulling the sections apart. Not entirely surprising - lots of boats have such, but I think in this case it comes from the ribs not being correctly fitted.
Also, it's hard to see from the photos, but it looks like the rib flanges weren't sitting flat on the hull sheet - they were pulled down to meet the sheet to weld initially, is that right? If so, my suggestion would be to simply cut the bottom flange off the existing floor ribs, so you are left with the vertical leg of the rib. Then, shear some strips of .100 sheet to fit the vee of the boat on one side, straight on the other. You'll stand these up against the ribs. These will weld or rivet (ideally both) to the side of the rib, then MIG weld to the hull skin of the boat.
The transom knee brace doesn't scare me - that's an easy fix. Oddly, it's actually the opposite of my Weldbilt theory - that's decent welding, but bad design. That's not write home to mama TIG welding there, but it's certainly passable for a boat manufacturer. Basically, all the transom strength comes from the wood core, but the knee brace (and it's reasonably beefy - not in thickness, but is a rigid shape) is welded to the thin skin, and is pulling on that. They tried to remedy that with the two 1/4" bolts, however out on the unsupported flange, they don't do much good - the knee brace is only rigid in the middle. Also, following that logic, the downhand MIG weld down each side of the brace doesn't do a lot of good - it's pretty much relying on that 2.5" of TIG weld at the top.
Simple fix there is to remove the engine, and shear a strip of sheet or plate that goes down the top of the knee brace a little bit (few inches, then wraps over the top of the transom and welds there. Basically, instead of knee brace pulling just on a flat piece of sheet, you want it also pulling on the top, where it has two bends to make it a little more rigid, and where you can increase the weld area.
You haven't mentioned this yet, but if you can access the bottom of the transom wood, see if there is a big gap between it and the outer skin. On some of those boats, the wood transom core is not attached to the bottom of the transom at all. The force of the motor pulls out on the top of the transom, and pushes in on the bottom. With the wood not attached, it starts pulling forward, flexing the back transom sheet, instead of transferring the force to the bottom of the hull, as it should. A row of 6 bolts/nuts and fender washers across the bottom of the transom wood, pulling it back tight against the aluminum skin solves this issue.
I'll be glad to elaborate on some repair suggestions if you go that route.
Last time I did a repair on a less than one year old Weldbilt, the bill was in the $400 plus range (granted, we did a redesign, so he'd never have a problem again, instead of just welding the broken stuff back together), and Weldbilt offered to pick up $50 of that.
