[FishStretcher]

The computer says ~110 lb, depending on how much welding wire is in it. That's for a 24" setback and a 3/16" center rib and transom interface. (The part that bolts to the real transom. the rest is 1/4" or 1/2" on the O/B mount plate.) I extended the center 3" rib higher and it didn't add much in terms of performance. But I suspect that if it went all the way to the top (and thru the swim platform) it might help. Maybe I can get a FEA run with that feature in some lunchtime this week. But I think I am narrowing in on a solution- additional returns in stiffness/strength are costly in terms of material or mass.

If this were fiberglass and as thin as this construction is in aluminum (they aren't made that way- they are usually lots thicker) then yellow and green colors should be avoided. But the stresses that hit the bolted joint from the bracket to the boat transom are at a plywood/fiberglass to aluminum joint, so repeated pounding might be problematic. Especially if there isn't a lot of gap filling/ stress spreading material in the joint, like 3M 5200 compound might do. Without that, you might see compressive failure/loosening/crush damage at that joint?

The more I think about it, fiberglass is the way to go, if you can build it right and get the 2 halves to share the load well. I just don't have that construction technique figured out yet. And I own an aluminum bracket that I am waiting to install.