Abstract: An exhaust muffler for mounting on the transom of an inboard or inboard/outboard motorboat around the exhaust pipes which extend from the transom. The muffler comprises a housing which has a pair of sidewalls each adjacent to one of the sides of the boat, so that the housing is approximately equal in width with the width of the boat at the stern. Inside the housing is a baffle extending downwardly from the top of the housing which directs the exhaust downwardly around the bottom of the baffle to reduce the noise emanating from the exhaust. The top of the housing preferably forms a swim platform which provides a functional and attractive appearance to a muffler located outboard of the boat. The large size of the muffler results in enhanced noise reduction without adversely affecting engine performance.

Abstract: A draining device for a muffler of a small planing boat in which engine cooling water is injected into the muffler. A draining hole is opened in the muffler, and to aforesaid draining hole is connected one end of a bypass hose with the other end opened to outside waters at a hull rear section.

Abstract: An exhaust muffler for mounting on the transom of an inboard or inboard/outboard motor boat over the exhaust pipes which extend through the transom includes a top which forms a swim platform. The muffler comprises a housing which has a pair of sidewalls each adjacent to one of the sides of the boat, so that the housing is approximately equal in width with the width of the boat at the stern. The top of the housing forms the swim platform which provides a functional and attractive appearance to the exterior muffler.

Abstract: A novel exhaust system for both conducting engine exhaust gases away from and aft of the personnel occupied portion of a marine vessel and protecting the sides of the hull of the vessel from damages thereto during docking or other "working" maneuvers of the vessel is provided.

Abstract: Two embodiments of outboard motors incorporating improved silencing systems for the exhaust gases of the powering engine. In each embodiment, a Helmholtz resonator is provided by a resonance chamber formed at least in part by a spacer plate that is interposed between the power head and drive shaft housing of the engine and which communicates with an expansion chamber of the engine through a tuning neck. In each embodiment, the effective volume of the resonance chamber of the Helmholtz resonator is varied in response to engine speed by delivering coolant to it from the engine cooling jacket and discharging the coolant at a restricted rate.

Abstract: A bubble silencer for use with scuba equipment is comprised of a flat flexible enclosure attached to a scuba regulator valve. Exhaust bubbles issuing from the regulator into the enclosure coalesce into large air parcels to be expelled at low velocity through a rearward exit port. The large size and low velocity of the exhaust bubbles leaving the enclosure are much quieter than the small high velocity bubbles issuing from the regulator itself.

Abstract: An underwater voice communicator in which the preferred embodiment comprises a pair of tapered tubes in communication with a diver's mouth. The tubes are constructed of a material having a sound impedance similar to the sound impedance of water. Sound energy issuing from the mouth of a diver is reflected down the length of the tapered tubes to an area of the tube that concentrates the sound for injection into the surrounding water.

Abstract: An exhaust silencer system for piston type internal combustion engines hag a wet-exhaust, having a muffler and a muffler bypass which contains water at slow and moderate engine speeds, the water being expelled by the exhaust gas pressure at high engine speed, opening said bypass to the flow of exhaust gases thus reducing the exhaust back pressure occurring in the muffler.

Abstract: A method and apparatus for reducing acoustic noise associated with the release of gases from a submerged device, such as a sea water battery. A flat piece of material, preferably polyurethane, is mounted onto the top of the device. The piece of material is provided with an outwardly extending lip on the lower surface thereof adjacent an outlet port through which the gases issue. The lower surface of the lip is preferably curved upwardly and outwardly away from the outlet port and is disposed immediately at the upper edge of the outlet port. Gas emitted from the outlet port immediately forms bubbles on the lower surface of the lip, and the bubbles so formed pass outwardly and upwardly along the lower surface and subsequently escape into the free water.

Abstract: A multiple flow marine muffler constructed of resilient material having an elongated generally cylindrical hollow shell with reduced diameter inlet and outlet portions, and longitudinally spaced pairs of opposed baffles within the shell which define a plurality of chambers decreasing in axial length from the chamber adjacent the inlet portion to the chamber adjacent the outlet portion. The several pairs of baffles are so shaped, sized and oriented as to provide multiple flow paths for exhaust gases and cooling water through the muffler, namely, a central straight through path for engine idle condition, a first pair of undulating paths in side by side out of phase relation, and a second pair of undulating paths in side by side out of phase relation which are oriented in the cylindrical shell 90.degree. away from the first pair.