-NEED HELP- Aluminum Boat Transom question

Hello all, i just tore out my old transom wood on my 16' Mirrocraft Northport Troller today and am looking to replace it. The boat transom is setup so you simply drop the wood in between the back aluminum of the boat and the transom. I pulled the old transom out and it is a perfect rectangle and exactly 1.5 inches thick. I could easily match it with plywood but do not want to go through the work of sealing. My idea was to simply buy 1.5" thick square aluminum tubing and stack it until i reach my desired height and then have it tack welded. It would be a solid 1 piece when completed and i could drop it in and bolt it on. Would this work and would it be strong enough? Also what thickness of aluminum should i go with for strength, 1/8 or 1/4, ill have a 40hp motor on it.
Thanks a lot, Max

I replaced my whole transom with aluminum. It was a combination of box and sheet 1/4" 6061 with vertical strengtheners inside the transom vertically in line with the outboard mounting bolts. I also run a 40 horse jet, the boat is a 14 foot Fisher Marine jon. It is rock solid but it was a real PITA to weld it. Will try and post some pics tomorrow so you can see.

Could probably get away with making a 1" square tube frame and a piece of 1/4 aluminum plate on either side. It's a good idea, as a welder, I'm ashamed I never thought of it! I've always made wood transom replacements from 2 pieces of 3/4 plywood laminated together. If treated properly and kept dry, will last a long time.


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Welding a stack of aluminum square tubing sounds like a great idea to me. Very strong!

I am working on my third plywood transom attempt which unless I dorf it somehow looks like a go.

First "prototype" was two 3/4" exterior plywood glues with titebond 3 and screws. Bad batch of plywood---many voids and delaminating without exposure to water!

Second "prototype" was three 1/2" exterior aracoply (no voids) laminated with Raka epoxy resin and biaxial fiberglass cloth. Did not get enough epoxy between one layer and made some bad cuts (not 90 degree) with a cheapo jig saw.

Third attempt looks like a success. Went with a slower hardener for the epoxy which gave me the pot life I needed to make sure everything was gooped up and wetted out completely. Bought a nice Bosch jigsaw that cuts at a square 90 degree thru 1.5" of wood and made the finishing cuts last night.

Now I am wondering if I should seal with this awesome Raka epoxy or do the traditional old school seal and paint.

Best of luck to you.

I made an aluminum transom for my Bluefin -
it consists simply of 1-1/4" square tube with two sheets of
1/4" plate laminated to each side. A little overkill, I know.
but, I had the materials on hand already so my cost was only for my time.
(oh - and $15 to have the 1/4" plate cut to size at a metal company).




I used an adhesive specifically for aluminum and some rivets.
this was probably 2 or 3 years ago and is still very solid today.
it held a 50hp outboard motor on a 1648 MV Bluefin.




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I lied. 1/8" plate with 2" square tubing reinforcement. The centre of the transom is double skinned with 4 vertical supports(two in line with the motor mounts). Excuse my crappy phone pics.
20170419_103518 by st1nkf00t, on Flickr

20170419_103459 by st1nkf00t, on Flickr

20170419_103408 by st1nkf00t, on Flickr

20170419_103400 by st1nkf00t, on Flickr

20170419_103333 by st1nkf00t, on Flickr

20170419_103315 by st1nkf00t, on Flickr

Thanks for all the replies, so i think my plan will be to do it just like the picture jonny did. What type of aluminum adhesive would you recommend? I will be using the adhesive as well as rivets.

Not silicone! Gluvit, GOOP Coat-it or 3M 5200 will all work.

as a signmaker, we use Lord Construction Adhesive.
a bit pricey to get started as they have special guns
and nozzels you have to buy in order to use the cartridge.
2nd choice would be 3M-5200.
There are several construction adhesives in the automotive world.
just make SURE it says it is safe for aluminum on the product.
if cosmetics are not an issue, a whole passel of pop rivets will work fine also.
PRIME and PAINT after assembly

I'd prime all areas to be glued ... Johnny has posted pictures of where 5200 corroded bare aluminum.