In a wet exhaust, cooling seawater is injected after the engine’s dry exhaust section. It cools the gas so approved marine exhaust hose, a waterlock and muffler can carry it overboard.
The installation has two jobs: release exhaust without excessive back pressure and keep seawater out of the engine in every realistic trim, heel and sea condition. Typical components include a mixing elbow, water-injection hose, waterlock, rising hose or gooseneck, anti-siphon device where required and hull outlet.
Major failure modes
- Carbon or corrosion restricts the mixing elbow.
- Exhaust hose delaminates internally or develops a soft spot.
- A waterlock cracks or is too small for drain-back volume.
- An anti-siphon valve sticks or its vent hose blocks.
- Excessive cranking fills the exhaust with seawater before the engine starts.
- Following seas, heeling or poor outlet geometry allows water back towards the engine.
- A failed hose or clamp releases water and exhaust into the boat.
Seawater intrusion can bend a connecting rod, corrode a cylinder or destroy a generator. Installation height cannot be copied blindly from another boat. It depends on the worst-case waterline, injection point, hose volumes, heel and back-pressure limit.
During prolonged no-start diagnosis, follow the engine manual’s procedure to prevent the waterlift filling. This may require closing the raw-water seacock while cranking, then reopening it immediately when the engine starts. Use a conspicuous reminder because running with the seacock closed will damage the impeller and overheat the engine.
Exhaust gas contains carbon monoxide. Fit and test suitable alarms, maintain ventilation and investigate fumes or a change in exhaust sound. AMSA warns that engine and generator exhaust gases can accumulate and become lethal.