Be aware that wherever you weld this to your hull better be super rigid or the hull flex will cause a crack at the weld joint. If you want uber rigid, run multiple smaller tubes stacked and plate it....you'll have to have bad luck and a big wrench to crush it.
I personally would avoid welding to the floor unless you can plate a section to ease the flex on the weld area. If the transom is rigid and well attached....its not going anywhere that a 20hp is going to hurt it.
I'd go 4043 on this one myself.
This brings up a good point. I currently have a small crack right in the stop of a weld on the transom brace that’s welded to the floor. This is what prompted this project and made me want to get on it before it gets worse.
Due to the shape of the hull I can’t go full width with the tubes. I can only get within about 1/2” of the sides of the hull. Should I stack two 1.5x3s and stitch them together then run a gusset at a 45deg angle to each gunwale? I thought I’d weld the current crack and dress it down then relocate the braces to a fresh area and put them on a plate like you suggest. I hate welding on aluminum any more than necessary due to the structural issues it can cause but I want to get it scotched once and for all.
