New Member - Replacing Transom

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RANGER94

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May 29, 2012
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Hello Everyone,

Great Forum! I already picked up a few tips.

I am working on my first boating project. Attached are pictures of a 12 foot aluminum boat that has been in my family for over 40 years. It is strictly a fresh water boat, and sits in the water from Memorial Day to Labor Day, at which point, it is pulled out of the water. An older 1975 Mercury 7.5 horsepower outboard is her engine. As you can see, there is an outer piece of lumber, which will be in the water, aluminum in the middle, then a inner piece of lumber, is used for the transom to support the engine. Both pieces of lumber are shot.

Now please be patient with me, I am not the handiest of men. Any help would be appreciated...

I cannot find marine grade lumber, and I know to stay away from pressure treated. Am I on the right track? I was going to Lowes or Home Depot and purchast a top quality piece of exterior plywood.

I have read that using Epoxy coating is the best way to protect the wood. What specific brand of Epoxy should I use? I assume I should coat both sides of each piece of lumber?

I am going to replace the hardware as well - is there a certain grade/marine grade to use or is stainless the choice? Also, what type of washers - the ones with the rubber on the inside or standard normal washers & bolts?

If you can see the pictures, I have several screws that serve no purpose. From a previous post, I was going to fill them in with 3M 5200. Does this sound sane? Actually when I was finished removing the wood and taking a look at what I got, I was going to consider to fill in all of the screw holes and start from scratch. Does this sound OK?

Any other words of wisdom, tricks, or advice would be appreciated. Thanks again for any help!!!

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I have to do the same thing to mine. I was going to go with exterior grade plywood, stainless hardware, spar urethane, and 3m 5200. From what I have seen that seems to be typical. I am sure someone else will chime in if I am too far off base though.
 
Johnzsmith is spot on.

Based on your transom caps and seats - I think you have a RichLine boat. It maybe a car-topper, but I can't tell from the pictures. I have a 196? Sportsman 14' V that I had to replace the transom in this year.

I used exterior grade non PT plywood. I think the brand at Lowes is called Arauco. I opted for 4 coats of Spar Urethane.

If your hardware is original it will be aluminum. I ended up having to drill most of mine out because turning it by hand snapped off the heads of the screws. Some of them I had to cut with my dremel as well in order to get them out. I replaced them with stainless steel bolts, screws, washers, and nylock nuts (also stainless). All hardware was coated with 3M 5200.

As for the screws with no purpose... I would actually drill them out and replace them with rivets sealed with the 5200. Second option would be replace them with stainless bolts and nuts coated with 5200. If they are below the waterline and aren't currently leaking - you may want to leave them as is.
 
I'm in the same boat urrrr uhhh different boat same situation... need to rebuild transom. I'm not an expert, but I have been looking at a lot of transom pictures online.

If I'm not mistaken, that external board used to extend further down, hence the extra bolts. Might not make a difference, but if the external wood expended down to line up with internal floor to transom brace... that would be structurally better.

As far as resin brands, I seem to recall the big box stores (Lowes, Home Depot, etc) carry Bondo. I ordered mine from US Composites online. Not sure why a lot of people recommend epoxy resin over polyester (probably a case of good (urethane), better (Poly resin), best (Epoxy).

Anyhow, I used the B435 Polyester resin years ago to build a custom subwoofer enclosure, but since then have found other uses… including fixing a leaky fountain. I can tell you this stuff is strong, light, and waterproof. A quart would be more than enough for your transom project and then some.

https://www.uscomposites.com/polyesters.html
 
Thanks for the help!

I went to Lowes and got external grade premium plywood. I also went to a local boat supply shop, and spent a small fortune on an Epoxy system. I plan to coat the wood with about 5 - 6 coats of the epoxy and then paint it white.

As for the screws that serve no purpose, I was going to remove the screws and just fill the holes in with the 3M 5200. I saw several previous posts where people had success with that technique.

This is a long term project, I will keep you updated.

Again thanks for the posts!
 
I used West systems 105 epoxy for my transom rebuild. 3 coats was plenty. Just make sure to keep filling the board edges with epoxy as it really sinks in, especially make sure to completely fill any small voids. Drill the bolt hole slightly oversize and run the epoxy through them as well to seal them up good.

Since you are going to paint over it, you shouldn't have to worry about UV affecting the epoxy. I put a couple of coats of UV inhibiting Spar Urethane on mine to protect the epoxy from breaking down over time.
 

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    New transom.jpg
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Hi Ringo,

That looks like a very profession job! I purchased the same - West Epoxy 105.

I like the look of yours with the Spar Urethane. How do you think in terms of light stability with the Spar Urethane compare to white paint? The instructions for the West Epoxy recommend an opaque white for the best stability.
But I like the look of yours better....
 

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