Definition
A wet exhaust is the arrangement used on most marine diesels in which raw cooling water is injected into the exhaust gas downstream of the engine, cooling it enough to be carried in rubber hose, silenced in water and discharged overboard.
Cooling the exhaust solves several problems at once: it allows rubber hose instead of lagged steel, it reduces noise substantially, and it lowers the fire risk of a hot exhaust running through a confined space.
The components that make it safe
The mixing elbow injects the water, the waterlock holds what drains back, and the anti-siphon valve breaks any siphon that would let the sea back into the engine. Hose runs, falls and rises are engineered, not convenient — the geometry is what keeps water out of the engine.
Why it deserves respect
The failure modes are serious: water reaching a cylinder, carbon monoxide entering the accommodation, or a hose failure filling the boat. Exhaust hose, clamps and the elbow are inspection items, not fit-and-forget parts.
Where you meet it
On nearly every recreational marine diesel and genset installation in the country.