Jon Boat Transom Replacement

fellas2

Recruit
Joined
Jul 3, 2019
Messages
3
Hi Everyone, new to the forum.
Recently retired and just bought my first boat. It's an older Sears 12' aluminum jon boat. The boat came with a trolling motor and it works well with the current wood setup on the inside of the transom. However, i'd like to go with a small outboard around 2.5-5 hp and in my inspection of the boat, i found that there was originally a wooden transom plate on the exterior which a previous owner had removed , (i'm assuming it was rotted) and the only thing remaining was the original aluminum rivets. I laid a straight edge across the transom and it's not perfectly flat. My plan is to take two pieces of marine plywood, treat them, then sandwich the transom with one on the outside and one on the inside using stainless carriage bolts. My question is will this work, what do i seal the plywood with, and should i use some type of caulking material in between the transom and pieces of plywood. Any input would be appreciated.
 

matt167

Captain
Joined
Sep 27, 2012
Messages
3,630
No, laminate 2 pieces of 3/4" or 3 1/2" pieces of CDX or better plywood. Use a good strong waterproof glue. Then seal it with fiberglass resin and glass if you want or you could just use spar varnish.. Then attach it how it originally was.
 

strokendiesel002

Petty Officer 1st Class
Joined
May 15, 2012
Messages
283
If you post a couple more times, you'll be able to add pictures, and give everyone a better idea of what you're describing.

Most wood transoms are 1.5" think as stated above, but probably way overkill for a 12' with 5hp. Either way, a half sheet of 3/4" exterior or Marine grade from your local big box should be all you need, and it won't hurt to have it 1.5" thick. I chose to use epoxy to laminate and seal my transom, then painted any part that was exposed. I first tried lamination with gorilla glue, but it expanded too much, so I cut it back apart, sanded and then just used the epoxy - I believe west marine, a picture of the material is in the Sylvan thread in my sig.

As far as the wood on the exterior of the transom, my understanding is that it helped prevent outboards from vibrating up and off the back of the boat when just clamping them on, as it gives you something to "crush" into. If the outboard is going to be through bolted, I really don't see the need. If it's going to be on and off, doing as you said, sandwiching the hull would be fine. You don't have to use epoxy as I did, one very popular choice is the Old Timers Formula (OTF). Do a search for member WOG and keyword OTF, you should be able to fine it from there.

Good luck, welcome and Congrats on your fishing rig!
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,310
No, laminate 2 pieces of 3/4" or 3 1/2" pieces of CDX or better plywood. Use a good strong waterproof glue. Then seal it with fiberglass resin and glass if you want or you could just use spar varnish.. Then attach it how it originally was.

not on a jon boat
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,310
most jon boats have either a single chunk of white oak about 1-1/2" thick by about 8" across the inside transom and a 3/8" marine ply or starboard scuff plate on the outside of the transom

the scuff plate is so you dont scratch the paint clamping and unclamping your kicker/motor/trolling motor as you yank the jon boat out of your pickup truck bed or off the camper to get it in your favorite back water fishing hole

I would use Woodonglass posted old-timers formula for water proofing if you want, or simply some oil based enamel, laminate a few plys of exterior plywood together with tite-bond III on the inside transom board and add your scuff plate of plywood or starboard to the outside.

the wood will pull your transom straight
 

fellas2

Recruit
Joined
Jul 3, 2019
Messages
3
Thank's for the replies. I'm gonna go with the old timers formula and marine plywood on both side. Last question is what type of sealant / caulking should i use between the plywood and transom. i have the transom sanded down to the bare aluminum.
Thanks again.
 

strokendiesel002

Petty Officer 1st Class
Joined
May 15, 2012
Messages
283
Wipe the sanded areas with acetone and spray first with self etching primer. Then finish with color of choice. Just be sure that whatever final paint you use is compatible with the S.E. Primer. Don't see a need to caulk around the boards. 3M 4200 would be fine for sealing the stainless steel bolts used to sandwich the 2 pieces of wood to the hull.
 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
I agree ^^!! The only concern is any holes drilled into the transom should also be Sealed with OTF and then coated with 3M-4200 to ensure water will not be able to access the inner regions of the wood via the drilled holes.
 

fellas2

Recruit
Joined
Jul 3, 2019
Messages
3
Would carriage bolts be ok or should i go with standard stainless hex bolts and washers ?
 

strokendiesel002

Petty Officer 1st Class
Joined
May 15, 2012
Messages
283
Stainless Hex with washers would be my choice, as you will be able to remove them from the 3M 4200 some day if needed.
 
Top