What Is a Transom?
The aft closing wall of the boat - the structure that carries the full load of an outboard engine, and quietly rots away if water gets into it.
The transom is the flat structural wall that closes off the stern of the hull. On an outboard boat, the engine hangs directly from it; on an inboard boat, shaft exits, platforms, davits and flap fittings all live on it. In traditional construction, it usually has a plywood core.
On an outboard boat it is the most heavily loaded structural element: engine thrust, weight and wave impact all end up in the transom. Its weak point is the same as a sandwich deck’s; water getting in through screw holes rots the plywood core over the years.
Flex test and protection
Flex test: If you load the engine leg up and down, any visible flexing or cracking in the transom is an on-the-spot test for a rotten core.
Brown seepage from screw holes: ‘Tea staining’ from wet plywood is a classic and clear sign.
Protection is cheap: Every hole made in the transom should be sealed with epoxy and bedded with sealant; repair, by contrast, is a major laminating job.
A single piece of advice for anyone looking at a second-hand outboard boat: do not talk price until you have bounced on the transom.