This boat came into our shop for transom work. Here is what we found when we opened it up, what we've done so far, and what to look for on your own boat. We'll finish it in the spring and add the completed photos to this post.

Why the core matters

Many fiberglass boats have a transom built like a sandwich: fiberglass on the outside, fiberglass on the inside, and a plywood core between them. The core is what makes the transom stiff. The transom carries the engine's weight and thrust, so when the core goes soft, the whole stern starts to flex.

What we found

The transom with its outer skin cut away. The dark wood is rotted core.
The transom with its outer skin cut away. The dark wood is rotted core.

Once the outer skin was cut back, much of the plywood was dark and coming apart in layers. Other sections were still sound. Rot doesn't stop at the edge you can see, so everything soft comes out, back to dry, solid material.

Rotted core across the stern, before removal.
Rotted core across the stern, before removal.

How the water got in

Water reaches a core through anything drilled into it: engine mounting bolts, a transducer, a ladder, trim tabs. If a hole was never sealed, or the sealant failed years ago, water wicks into the wood and stays there. Ontario winters make it worse, because water in the wood freezes and expands every year the boat sits out.

Where the job stands

Rotted core removed, the area rebuilt and faired.
Rotted core removed, the area rebuilt and faired.

With the rot removed and the area dry, we rebuilt and faired the surface, then cut new fiberglass cloth to the shape of the repair.

New fiberglass cloth cut to shape and clamped in place, ready to lay up.
New fiberglass cloth cut to shape and clamped in place, ready to lay up.

In the spring we lay up the new fiberglass, fair it smooth and finish it in gel coat to match the hull. The finished photos will go here.

Signs your transom or deck may be wet

  • The transom flexes when you push hard on the engine with the boat on the trailer.
  • Cracks in the gel coat around fittings or engine mounts, especially spider cracks.
  • Rust or brown stains running from screw holes.
  • Water weeping from a fitting or screw hole after the boat comes out.
  • A deck that feels soft or springy underfoot.
  • Screws that spin and won't tighten.

Caught early, it's a smaller job

A wet patch around one fitting is a much smaller repair than a whole transom. If you've noticed any of these, send us a few photos through our fiberglass repair estimate form and we'll tell you what we see.