Primarily used with in-line mufflers on sport fishing boats and other vessels which are frequently required to back down. The surge chamber is mounted between the engine and the muffler, with the exhaust flowing down the angled arm and out the straight (open) end. As the vessel moves in reverse, should water be forced backwards through the muffler, it is trapped in the closed end of the surge chamber, creating a back-pressure which helps prevent the flow of water into the engine.