15 to 20" Transom Conversion Question

My plan is to raise the transom to 20". At first I was thinking about just enough aluminum to do the job; however, after thinking about all those holes, I am wondering if it would be better to weld on a larger piece.

My thought now is to leave the existing transom "skin" and weld on a larger piece to the outside that would cover most of those holes. I'm thinking that I would size it by going just inside of the rivet holes that correspond to the angle pieces that run along the sides and bottom of the transom wood.

Is there anything wrong with having two layers of aluminum sandwiched together like that? I don't see how, but this is my first project.

*On a side note, I am planning to make new corner pieces, to modify the knee braces, and to go after the back end with a wire brush before getting it welded.

This is what I have.

All aluminum.

If your gonna weld, get rid of the wood and just build you a entirely aluminum transom, adding to the height at the same time.

It did have a jackplate on it like the one pictured.

The wood was shot so I had get into it either way so I'm raising the transom up instead of reusing the jackplate.

All aluminum though? How thick of a plate would I need to compensate for not having wood?

It's possible to build one out of tube like the boat co. does them now, and just put a skin over them, rather than use a thick aluminum plate. It's also lighter and much easier to work with. You'd need a plate about 1/2" thick to get the same function as the tube type transom. See the link below for a pic of one of the members transom rebuild. ( I apologize for not remembering the thread and members name ).

https://i1083.photobucket.com/albums/j383/Orion_134/IMG_20110905_203424.jpg

I was wondering how they made all-aluminum transoms. So is that 1 1/2" tube? And what about wall thickness? I would think 1/8, 3/16, or 1/4...?

The tubing on mine is 2" x 3" x .100" wall thickness. When I extended it upward I used a 2" x 4" x 1/8" wall rectangular tube . I'm using a 25hp Mercury 4 stroke, and it is plenty strong enough for that. If You are going to use a bigger motor, either HP or weight wise I would probably step up to 3/16" thick.