Abstract: An exhaust relief outlet is provided in the lower end of a marine propulsion system lower unit for providing exhaust relief to an internal exhaust passage formed in the lower unit. The exhaust relief outlet is provided in the rear end of the lower unit and is disposed adjacent an area of restricted exhaust flow formed by converging walls of the internal exhaust passage. The exhaust relief outlet is located so as to discharge exhaust into the upper half of the path of the propeller as it rotates about a propeller shaft. The exhaust relief outlet both relieves exhaust pressure within the exhaust passage and provides controlled ventilation to the propeller for allowing increased acceleration and planning ability for a marine propulsion system.

Abstract: A marine propeller (4) has a plurality of blades (12, 13, 14, and 15) each with an integral addendum (34) extending rearwardly from the trailing edge (30) of the positive pressure surface (26) of the blade. A particular combination of blade area ratio and blade rake is provided to enable quick acceleration to a high-speed on-plane condition in blade surfacing racing applications, and without bobbing up and down. The blade area ratio is at least 40%, and the blade rake is 10.degree. to 25.degree..