Replacing Transom Board (Wood) on an old Aluminum Boat

I replaced my old wood board on my aluminum boat last year and now it’s rotting again. The gentlemen at the local hardware store said that the board was marine type, but clearly it wasn’t. I believe it’s about 1/2″ thick.

I’m wondering what type of board people use to replace? Or what people have done that works. **Not trying to break the bank fixing it but I don’t want to replace it every year either.

Also, where do you find it? Home Depot? Online?

Which sealant (if any) should I use that works the best.

Thanks!!

Are to talking about the actual transom, or just a board on the transom that your motor clamps onto? Pics might help.

at 1/2 inch, it’s gotta be the clamp board.

big_g wrote:

at 1/2 inch, it’s gotta be the clamp board.

Good point.

The board that the motor mounts to. Is that not the transom board? Sorry, if I’m using the wrong terms here. I found a pic to help describe what I’m talking about.

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jtstarvinmarvin wrote:

I replaced my old wood board on my aluminum boat last year and now it’s rotting again. The gentlemen at the local hardware store said that the board was marine type, but clearly it wasn’t

The gentleman may not have been wrong. A year ago I did a boat renovation and looked in to different plywood options.

Marine grade is more about structural integrity. Meaning no knots or issues. It is not treated with anything to help with rot or water issues

Green treated does have stuff that helps prevent rot. However there are indications on a couple forums(IDO and WC best resources anywhere I could find surfing the net) that what’s used for the green treating will oxidize with aluminum. Making it a bad choice for tin boats.

Good or bad I bought regular plywood in a good grade and then put Thompson’s water seal on it.

Too soon to tell if putting the sealant on was the right choice. It spends most of the time indoors now and not enough time on the lake.

Just my opinion, but I used a well sealed piece of White Oak…
A little pricey yes….it was still good 5yrs later when I sold the boat..

I replaced my old boats transom last year. I bought marine grade, expensive, but the boat was in pretty decent shape and wanted to do it right. I got a 2 part epoxy and gave it 2-3 coats. The new owner should never have an issue with it for the life of that boat.

4 coats of Spar Urethane and 2 laminated sheets of 3/4″ BCX exterior grade plywood is what I used to build my new transom board this month. I’ll let you know in a year if we’re still going strong.

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I’d be temped to use (and have in the past used) oak as already suggested and seal it well with Spar poly. Even raw oak is slow to rot, but seal it well on both sides and it should last decades.

Second would be a piece of spruce sealed the same way.

The failure point on all flavors of plywood is usually the exposed edge. as soon as moisture gets between the layers–and it always does–the breakdown starts.

Grouse

I have seamless aluminum trim that protects the top of that board. Will it stay 100% dry? Probably not, but that’s also why a person needs to pay close attention to sealing up the edges.

Will my transom board last the life of the boat? I don’t know, but I bet it’s going to last a very long time. Pretty happy with how that build turned out.

In my duck boat I used a 1 x 6 piece of solid composite decking. It’s a little pricey, but it sure beats having to replace it every few years or having to seal the hell out of a piece of wood. I did learn that you have to pre-drill the holes if you want to put screws into it.

Do you guys sandwhich two boards with the aluminum between them? Or just a board on the inside?