Ventilated outboard motor-mounted pumpjet assembly

摘要

The invention features a unique surface configuration which fosters atmospheric ventilation and thereby uncomplicatedly reduces drag which is normally associated with implementation of shrouding for a marine impeller. Typical inventive embodiments include a blunt trailing edge and a circumferentially stepped impeller shroud (below the blunt trailing edge), the harmonious union of which affords a generally smooth and unbroken surface which encourages drag-defeating air circulation. During marine navigation, circulation of the air generally describes a path wherein the air first travels linearly downward along the blunt trailing edge, then travels curvingly downward (both clockwise and counterclockwise) along the circumferential step, forming a circumferential air pocket which extends a backward distance increasing in accordance with increasing navigational speed; upon attainment of a threshold navigational speed, the air pocket (virtually) completely surrounds the shroud. According to the invention, many a conventional outboard open propeller assembly can be facilely converted to an inventive outboard shrouded impeller assembly which produces equal or superior performance.