Subject: Transom/outboard mounting holes
Date: Mon, 12 Oct 1998
Dear Rot Doctor:
I recently installed my outboard onto a brand new boat. The transom is made up of a sandwich of 2 layers of fiberglass with a plywood core. I realized that I did not properly seal one of the mounting screws (that is below the waterline) and water leaked through it into the boat. My concern is the wet wood core in the transom. The wood is not rotted but it is wet around the screw hole. I only had the boat in the water a couple of times before I realized the problem so this has not been a long term saturation. How do I ensure the wood is dry before I seal the bolt again? What if all of the moisture is not removed when I reseal the bolt? How do I know if all of the moisture is gone. Will rot develop even if no new moisture gets in? Should I use the CPES on the wood before I seal the bolts? What is the best way to protect the wood in the transom around the other 3 mounting holes should the sealant fail? Help!!
You are a wise man to get after this problem now, before damage has been done.
Pull the bolts that may have leaked water, and then get a hair dryer on high air/low heat, prop into position blowing into the hole, and leave it for a couple of hours. Take it away and then apply our CPES to the holes, putting in as much as they will accept. You might want to do this twice. allowing 3–4 days for cure-time between applications. Make sure to get the top part of the hole as well. Then re-install the bolt using polysulfide marine sealant, such as 3-M 101 (do NOT use silicone!). To do this correctly, apply the sealant, screw down until there is about 1/8″ remaining between the bolt and transom, allow the sealant to cure, and then screw down the bolt. Trim off excess sealant. This will give you a watertight seal.
If I were you and going through this process, I’d do it for every transom through-bolt. This will give you protected wood and sealed penetration all the way around.
Come back if you have more questions.