Sealing the Boat Transom Fiberglass Repair – Boston Whaler 13 Restoration – Part 10

Now that the weather is warming up here in North Carolina, I can finally start working on the hull and the boat transom. The transom fiberglass repair will consist chiefly of patching in all of the holes with a permanent fix. The only holes I won’t fix are the ones for mounting the engine. This is a 1966 Whaler so as you can imagine, there are a plethora of holes that have accumulated over the years.

Steps for the Fiberglass Transom Repair

Drilling out the Holes

drilling out holes in transom
In this shot, I drilled out the holes in the hull close to the transom, All of the holes in th transom were drilled out as well

I’ll be using the same technique I used on the inside of the Boston Whaler 13. Basically, I drill out the hole to accomplish two key things. First, I’ll be exposing fresh material which will give the epoxy patch to adhere too. Secondly, I’ll be beveling the hole so that the patch will be wider on the inside than the hole itself. I cover this in more detail in this article. Repairing small holes in fiberglass

One additional benefit of opening up the holes by drilling is being able to examine the quality of the wood underneath. 

This is especially important the closer you get to the bottom of the transom. That area is the most likely to experience rot within the fiberglass transom. I was lucky in this regards, as there did not appear to be any rot at all.

Patching the holes in the Fiberglass Transom Repair

After I’ve drilled out the holes, I vacuumed out the holes and gave al of them a small squirt of acetone to prep it for the patch. I’ll be using thickened epoxy for this step. I used the TotalBoat 5:1 slow setting epoxy for this. By adding a small amount of milled glass to the mix, I was able to get a somewhat thicker consistency.

I used a small syringe to inject the thickened epoxy into the holes. Now for the bit of oddity. After injecting the holes with the thickened epoxy, I applied a nit of masking tape over the hole. The transom is almost vertical. I put tape on the hole to hold the epoxy in place. I wasn’t sure if the epoxy would glue the tape in place but it actually doesn’t matter since I will be grinding these areas down a bit.

Applying a Glass Patch Over the Repair

After letting the epoxy cure for a few days I went back and sanded a concave dip over each hole I repaired. I took the opportunity to grind the tape off as well. The concave dip is to make room for a fiberglass patch. I’m a firm believer that any hole you patch on your boat should be reinforced with a bit of glass over it. I used a Wen sander/polisher with a sanding disc (60 grit) to get those divots deep enough for a layer of glass.

Once all of the holes has been sanded down I cut out a number of small patches using 1708 fiberglass. I opted for the 1708 as it is a combination of woven and chopped strand mat. It is sewn together so does not have a styrene binder holding it together. It is however a bit thick. In retrospect I should have used just a thinner woven mat. In any event, this worked out fine but required a bit of extra sanding.

Next, I mixed up a batch of the TotalBoat 5:1 slow epoxy resin. Using a chip brush, I applied a light coat to each hole. I then pushed the cutout 1708 fiberglass onto the resin and brushed more resin over it. Once there was enough resin I used an aluminum fin roller to roll out any air bubble and make sure the fiberglass mat was thoroughly saturated.

Fairing in the Patches

Once the fiberglass patches were cured, I ground each patch and the surrounding area down. I didn’t grind the fiberglass patch away, just enough to allow for some fairing compound to cover it. Applying the fairing compound is fairly straight forward. I used the Totalboat TotalFair. Easy to use, mix equal quantities until you have a uniform green color.

Once the fairing compound is blended I simply used a putty knife to lay down the first layer. I use metal putty knives, I find that they allow me to be more accurate in the amount of fairing compound that I put down. They are also superior in feathering in the compound so that you can easily blend it in to surrounding areas.

Final Steps in the Transom Fiberglass Repair


Once the fairing compound cured I sanded it down to blend it in to the surrounding areas. I actually repeated this process two more times. I did use an interesting trick to see where there were areas that needed additional compound. Using a flashlight, hold it almost parallel to the surface. This will highlight any shadows that of areas that need additional filling.

The final step in getting the transom ready for primer and paint is to sand it all down. I stepped up the sandpaper on the random orbital sander to 120. By this time, most of the surface had already been sanded with 60 and 80 grit paper. Going to 120 grit gave me a uniform surface which should accept the two part epoxy primer that I will be using on the hull and transom.

Next, I’ll be working on the hull. There’s some a lot of fiberglass repair work that needs to be done there. I’ve actually been working on both side by side but wanted to split up the effort as there are two very different methods of repair I cover on each.

You can watch the video version of this article here: Sealing Up the Transom Holes and Fairing

The entire series on this Boston Whaler 13 restoration can be seen here: 1966 Boston Whaler 13 Restoration

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