Changes

The exhaust system can be a dry stack routed up the mast, or a wet system exiting the stern or side under water. In the wet system, seawater circulates in a jacket around the exhaust to cool it. Cast iron jackets tend to rust out after a few years. Intuitively, you may not like large underwater openings protected by an inverted plumber’s trap. Also, the pumping losses on the engine will be greater with a wet exhaust. But anecdotally more boats have had stack fires than have been swamped by wet exhausts. Wet exhausts are cooler, and use flexible hosing. Wet exhausts are also quieter, use a smaller muffler, and don’t broadcast soot or [www.npi.gov.au/resource/particulate-matter-pm10-and-pm25 PM10 pollutants] on the boat deck. They only soot up the hull when the boat rocks or yaws to expose the outlet.