Rot Doctor


Subject: Rot in transom on 19 foot Bayliner glass boat
Date: Thu, 23 Mar 2000

I bought a 1983 19-foot open-bow Bayliner runabout from a friend for $500 The engine is an inboard/outboard Volvo Penta that is cantilevered out from the transom. That is, it is supported only by the transom.

The boat looks good, and the exterior of the hull is in good shape. The only significant problem is the transom which has developed some rot.

The transom still supports the engine, but the bottom bolts and washers that hold the support ring have sunk into the soft rotten wood of the transom. I removed the engine, and now I intend to repair the rot.

I probed the rot with a thin blade. It seems that the rot only extends halfway up the transom on the inside. I thought that I might repair the boat in this manner:

1) remove the hexagonal ring that supports the engine and the outdrive (it is held in by large bolts)

2) working from the inside of the hull, scrape out the rotten wood down to the glass skin of the hull while leaving the solid wood in place. [Or do you have a product that will restore this wood (i.e soak into it and harden it) without scraping it out?]

3) put in new wood coated with resin,

4) glass over the whole inside of the transom to unify the repaired area and the area that I left alone

5) cut an aluminum plate to fit around the transom opening that the outdrive fits through, and drill bolt holes through the plate. (The transom holds so much weight that I think I’ll feel better if it were stiffened with this plate)

6) reattach the hexagonal ring and remount the engine.

What do you think? Do you have other suggestions? What products would you recommend? Quantities? How should I treat the hole that the engine/outdrive passes through?

Thanks for any help you can provide.
Jim C.


Interesting…I didn’t know that Bayliner built boats that hung everything from the transom. With this in mind, I completely agree with your thoughts about the aluminum plate. I’d make it at least 1/4″. I’ve used it before in similar situations and it’s not too expensive to get a fabricator to cut it to size, radius the corners, grind the edges and drill the fastener holes.

But anyway, back to the rotten wood. Your planning sounds well thought through and workable. Get as much of the bad wood out as you can with whatever you can hook in there with. You might even make up a probe/hook out of a piece of re-bar. Anyway, once you’ve removed all the wood that you can, wait for a few days for the remaining wood to dry out a bit. You can even prop a hair dryer in place and turn it on high-fan/low-heat and let her blow to help the drying.

Now, it is essential that you soak the wood that remains with CPES (Clear Penetrating Epoxy Sealer). The CPES will harden any soft wood that remains, and, equally important, significantly reduce any future rot fungi problems (we have never seen rot return to wood that has been treated with CPES). If you don’t do this, then you will have a high risk of the rot continuing again even after the transom is sealed. For your application a 2-pint unit might do it, but I guess for not much more I’d buy the 2-quart unit and be sure that you have enough.

Getting the CPES in the bottom wood is no problem because it can be poured in. The sides and the top wood will require that you use either some sort of stream-injector (such as out Injection Kit with the syringe fitted with a needle) or spray. We sell the little spray kits and cartridges, which you can also buy at some auto supply stores. I would suggest that you either open or drill a small hole near the bottom of the transom so that you can see and catch the CPES after it has flowed down. It can be re-captured and re-used. The idea here is to keep flowing the CPES through and around the wood so that it has maximum opportunity to reach all areas. You can close the hole in the bottom after the CPES has cured with a bit of Epoxy Filler.

After the CPES treatment, wait at least 3 days for the CPES carrier solvents to evaporate away. The epoxy resin in the CPES may take a week to start to cure, but that’s okay since the curing process will continue in the absence of air.

Then go ahead with your wood piece fill. After the replacement piece has been cut and trimmed to an approximate fit, be sure and treat it with the CPES, paying special attention to the edges and end-grains. Let the wood absorb all the CPES that it will. This will give you good protection against rot in the new wood.

The new wood should be bedded in a soft putty made from our Layup & Laminating Resin and coarse sawdust. This same putty can be used to fill all gaps and holes that remain. It’s important that you use our resin, since it is super-strong, very slow setting and retains a slight degree of flexibility after curing, which standard epoxy resins do not. Don’t even think about using a polyester resin for this process. It hasn’t the strength or long cure time that you need.You’re now pretty much free to glass over the inside of the transom, install the aluminum plate and hook everything back together.

What would you need? First, a 2-quart kit of the CPES (Warm Weather Formula if you’re working at temperatures above 50F, Cold Weather if the temperatures drop below 50F — and the Cold Weather is fine for temps up to 75F). And you’ll need some Layup & Laminating Resin, at least 2-pints and maybe 2-quarts. I can’t really recommend which because I’m not looking at the volumes. The better the fit of the replacement wood then the less of the L&L Resin you will need. I’ll leave injection kits, sprayers and Epoxy Filler up to you.

Hope this has been helpful. Come back if you have additional questions. We’ll help in any way we can.


Note: Current pricing on all our products can be found on the Product Information page.