Stripping rotten untreated plywood
The transom of a power boat is the strongest part of the vessel. It has to transmit the full power of the engine to the rest of the hull, as well as carry the pounding of the hull back to the engine. The great forces exerted between the engine and the hull come to a focus at the transom.
New marine plywood, coated on
Eventually, the transom may deteriorate and weaken to the point that your boat is not seaworthy.
Your boat is not lost if the transom has lost its integrity. We can either strengthen it or replace it altogether.
Front of transom
Plywood is a great material for marine construction. It does not suffer from fatigue as does polymer panels, nor loose strength with age. In fact, wood gets harder as it gets older.
The problem is that most boat manufacturers do not use treated plywood.
Fiberglass layer applied and
Like the boat manufacturers, we use plywood made for exposure to wet environments. It's made with a waterproof structural adhesive to bond the plies together. The key is that we use pressure treated plywood to resist decay.
Closeup of a corner.
Pressure treating adds quite a bit of moisture to wood, so we use kiln dried plywood. After pressure treatment, the wood is dried in an oven at the mill to make it dimensionally stable. Plywood that is not kiln dried cannot be used for decks and transoms because it will warp.
A transom being installed
Some companies use plastic materials as the load-bearing material in replacement transoms, reasoning that the plastic will not rot. While it is true that plastic is more water resistant than bare wood, treated wood encased in fiberglass will resist decay almost as well as plastic.
Wood has a tremendous advantage over plastic materials: Wood will not form stress fractures. Under the constantly fluctuating forces experienced under load, a transom will flex and bend. This movement will cause fatigue in plastic materials but not in wood.
As time and usage accumulate, a polymer transom grows weaker but wood remains as strong as ever, perhaps even strengthening with time!
A properly installed wood transom made with treated marine plywood and encased in fiberglass can outlast a plastic one.