Abstract: A silencer quiets the exhaust output from a marine engine by injecting a spray of cooling water into the exhaust passageway to mix with and cool the exhaust gases before output from the passageway. The exhaust passageway preferably enlarges substantially in cross-sectional area in the region where the mixing occurs between the injected water and the exhaust gases for enhancing the cooling effect. An inlet scoop receives water as the boat moves forward, and the water is forced through a line and into the exhaust passageway in a way that breaks the water into drops for contacting and cooling the exhaust gases. A mute that is preferably conical in shape and centered in the exhaust outlet also cooperates to reduce the exhaust noise.

Abstract: A deep-V tunnel stern boat has the forward portion of the tunnel shaped for uniformly distributing the resurgent flow across the width of the tunnel and for smoothly forming the entrance curve to the tunnel to optimize a suction tending to lift the water into the tunnel. This is done by recessing port and starboard halves of the tunnel into the sides of the hull bottom so the tops of the tunnel halves are approximately parallel with the sides of the hull bottom at the deep-V angle and meet at an obtuse angle above the keel line. The tops of the tunnel halves are gradually shaped into a semi-cylinder around the upper half of the propeller, the tunnel sides are flared outward aft of the propeller, and exhaust ports are located in the flared tunnel sides. Such tunnels are also adapted for twin tunnel stern boats.