Replacing the Transom

The transom is an important structural part of the boat, so when you rebuild it, you want to do it right. Before you took the old one out, you should have, of course, measured the thickness of the old one. When you rebuild the new one, you want to get it as close as you can to the original thickness. You want to be careful not to go too thick- Remember, the outboard has to attach to it, and if it's too thick, the clamps might not fit!

The transom on this particular Glasspar posed a little bit of a problem. It is not flat- it has an outward curve to it. When I tried to put a solid sheet of plywood in, it just forced the outer skin of fiberglass (which is less than 1/8" thick) flat. So, I decided to laminate the first layer in pieces, which would allow me to conform to the curve better. After this, I could put solid sheets of plywood in to make up the full thickness. I need a total thickness of about 1 1/4", and I'm using 3/8" plywood- so I will build up 3 layers of it, giving me 1 1/8", and then a layer of fiberglass over that.

Each layer of the new transom is laminated in using epoxy, thickened with a filler. Apply a generous layer of it to the inside of the transom, as well as to the plywood pieces that you are laminating in. Don't be afraid to use PLENTY of epoxy for a good bond- You want it squeezing out the edges of the pieces as you clamp them in place.
The first layer of the transom, pieced in. Along the top edge of the transom, clamps can be used to hold everything in place. That 2 x 4 is 'wedged' in to the hull forward, to provide outward pressure on the center of the transom to keep it's curve. You should be somewhat precise in cutting the pieces of plywood, but small gaps are OK, You can easily fill them with epoxy. You won't be able to reach all the way to the bottom of the transom with clamps- But you still need to clamp it down somehow. I like to use drywall screws with plywood washers driven through the transom. You'll have to fill the holes later, but it holds everything good and tight. A word of advice- I like to spray the screw threads and the plywood washers with silicone lubricant before I drive them in- So they don't stick to the epoxy.

Once the resin has cured on the first layer, the next two can go in place. Although it holds it's curve pretty well at this point, To be safe, I continued to use the 2 x 4, wedged into the bow of the boat, to provide outward pressure. The plywood is cut as accurately as possible along the bottom and sides, but just kind of 'ballpark' along the top of the transom. I'll trim it to the exact shape later. Also note that I'm just covering all the holes in the transom- the drains and the bolt holes for the motor mounts. I'll re-drill them later, once the transom is done.

The next two layers went in as solid sheets, which went a lot faster. They are installed in the exact same way, by laminating them in place with plenty of thickened epoxy. There are a total of three layers of 3/8" plywood there now- So the wood part is done. Notice how the area around the edges is filled with the thickened epoxy, and how a 'fillet' is formed with the excess around the edge.
Once the epoxy was cured, I cut the top of the transom close to the final size around the fiberglass on the transom. Then, I used a grinder with a 40 grit sanding pad to get it exact.


Now that all the plywood is in place, it can be glassed over. The fiberglass will serve two purposes- First of all, it will provide some extra strength. It will also seal off the transom, and keep water from getting to it, causing it to rot again.

The first layer of Fiberglass is on now. One more to go!
Now for the final layer of fiberglass, which will add some strength as well as serve as the inside 'skin' of the transom. I used 1708 Biaxial cloth, which is a HEAVY cloth made from a layer of 17 oz cloth 'stitched' to a layer of 3/4 oz mat. It provides lots of strength, and a quick buildup. It does soak up a lot of epoxy, though, so mix plenty! I also went all around the edges with 3" tape.
That does it for the transom- At least for now. All that's really left is to drill the holes for the drains, but that won't be done until the boat is put back together. The end result is a transom that's about the same thickness as the original, but is considerably stronger, as it's made from better materials- and FAR better sealed against water. This should last another 50 year with no problems!
Main