Marine Exhaust Systems – How They Work

Marine exhausts systems are an important and often overlooked part of a marine engine. Most vessels have a wet exhaust system. Salt water is injected at the riser the outlet for exhaust from the exhaust manifold. This mixture of exhaust gas and water is then passed through a series of bends until it exits the boat, preferably at the stern.

Exhaust gases mixed with salt water create a highly corrosive compound. This is why exhaust systems are commonly made using non-corrosive components such as nitrile rubber reinforced hose (brown not green stripe), galvanized steel, fiberglass or plastic. The purpose of these components, which vary in size and shape depending on the engine size and layout of the engine room, is to prevent hydraulicing of the engine. This is caused when an engine has filled with salt water which has entered via the exhaust and can cause extensive damage if left for more than two hours. Water enters the exhaust from wave action at stern and poor exhaust design. In some ocean conditions, such as a following sea, water can be forced back up the exhaust when the engine is not running. Poorly designed exhausts allow water to flow back and fill the...