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Marine exhaust systems for inboard engines can be divided into two basic types—dry and wet exhausts. Dry exhaust systems have been around the longest but are now found primarily on commercial vessels or other specialty applications (high-performance craft, etc.). The basic job of a dry exhaust system is to carry hot exhaust gases overboard through a series of metal pipes. These pipes typically extend vertically from the engine and into a protective stack, where exhaust gases are then expelled above the decks and well away from the vessel.

Wet exhaust systems are more popular with recreational boats and are the focus of this article. They use water to cool the exhaust gases—and quiet engine noise—prior to discharging it overboard. Another benefit of this approach is the additional installation options it provides builders, as the cooled gases allow the system to now be routed horizontally to the exhaust outlet. Reduced temperatures also mean other materials (rubber, fiberglass, etc.) can be used in the system.

How they work

Water-cooled exhaust systems inject cooling water into the exhaust via an exhaust riser or mixing elbow, where the exhaust then pushes the water out of the exhaust outlet. Exhaust cooling water is typically provided by the engine’s raw water pump although a second pump may also be used (depending on the system).
Most installations will also include a muffler located between the riser and the discharge outlet. This not only reduces engine noise but also gives errant water entering the exhaust outlet a place to collect.