Aluminum Transom Build Issues

[BrayD]

Hey guys - new to the site but there's some awesome info here. Hoping to tap into your vast knowledge to help me out with a project I'm working on for a buddy.

Per his request, I'm building up the transom so he can run a long shaft motor. Replacing the wood with aluminum, patching up the skins, etc.

The transom build itself is pretty straight forward. I got that knocked out then moved on to patching up the skins. Note that the transom photo shown is in process, I added more supports and plate work.

I sourced some 14ga aluminum and cut a patch plate. Butt welding aluminum this thin is giving me serious issues. Even looking at it with the TIG causes local expansion and deformation. I can't keep it flat, impurities in the corroded OEM plate is giving me welding issues, etc. It's a big challenge all around. With the issues I'm having with this piece, I'm hesitant to start the patchwork on the actual boat side. I stopped progress with this piece so I can still abandon the patch repair if I want.

Is this the proper approach? Would you guys go about it differently? I'm considering welding the patch plate right to the transom, then trying to weld the skin to the transom at the same seam line. The additional mass would pull heat out, help me keep it flat, etc. The downside is that it's then welded to the transom so removal in the future would be a bear.

I've read of guys brake bending a U shaped cap that would extend about 2/3 of the way down the transom, inside the OEM skins. Drill/rivet through the skin, plate, and transom to secure everything. I don't have a brake that wide, plus there would still be a thickness differential between that U shaped cap and the OEM skins. I feel like I need to fill the gap somehow, hence the approach to weld in the patch plates.

What do you guys think?

 

[DaleH]

Not sure where you are but I have a sheet of 5052 alloy that would do the transom in one piece with stuff leftover ...

I myself would go for an new 1-piece panel and I would bolt them together using stainless steel hardware but FULLY insulated from the tin. That means adhesive-lined heat shrink on the bodies of the bolts and nylon washers “underneath” the SS washers that bear up against tin under the bolt heads and the nylok nuts.

 

[CTilton]

You are doing a nice job! If you can get your hands on a sheet of .0125 at least, I used 3/16 on one I recently did with forward reaching knee braces over a pocket tunnel. Is much easier to weld being able to lean on thicker material heat-wise.

 

[BrayD]

Thanks for the replies. Both are solid recommendations.

DaleH - I'm in Central Illinois, so snagging your sheet likely wouldn't work out so well, haha. I appreciate the offer though. I was hesitant to sheet the whole thing at first, as it's only secured below the transom (you can see the brake bends on the bottom of the OEM piece). Bolting the whole thing in multiple locations would be super solid though. No need to use the existing mounting configuration if I go that route.

Ctilton - Thicker material is a good idea too. I was stuck on the thought that I had to use the same thickness as the original skins, but in reality the only thing that contacts this place is the motor itself. I could use whatever thickness I want. The tube transom is made from .125" wall tube and welded up awesome. My welder is happy with that material thickness.

 

[CTilton]

for mine, I did add some weight with boxes and heavier material but it should be a battle tank.

I had some issues with the old inner transom wanting to bow out , just did my best to hold it in.

 

[CedarRiverScooter]

I would just tack weld it in a bunch of places, then seal it with some goo like 5200 or epoxy.

Looks like your sq tubes will handle the HP!

 

[BrayD]

I thought I'd give it one last try before spending money on different material. I found that using thick aluminum chill blocks as backing plates worked extremely well. It kept everything flat, pulled the heat out and helped trap argon. I was able to weld up both sheets without too much drama. That said, if I end up doing this on another boat I think I'll explore other options. Welding up the patch plates took a lot of time.

It did warp quite a bit, but I think it'll be just fine after it's all bolted together. The cap is a piece of .125" wall thickness C channel that I clearanced on the mill. Each of the legs are only .040" thick now and I have to tap it on with a dead blow. Everything is pretty snug.

I shouldn't have any problem welding up those big gussets and getting everything bolted up tomorrow. Should be on the water Tuesday.

Thanks again!

 

[DaleH]

That came out great!

 

[lckstckn2smknbrls]

That came out great!

+1

 

[jethro]

Yeah, that transom is way better than new. Nicely done.

 

[CTilton]

Very impressive!

I think you nailed it!

 

[BrayD]

Thanks everyone! I got it buttoned up yesterday and my buddy is picking it up after work tonight. Feels good to hang my hat on this one.

 

[CTilton]

Give us an update how did the testing go ? Was your friend happy with it?

 

[BrayD]

Give us an update how did the testing go ? Was your friend happy with it?

Super late on the update - sorry about that. I'm researching for another project and saw your inquiry.

He was super happy with it! Said the transom is solid and the boat tracks straight as it should. I haven't heard from him since so I assume as is well, haha.