a propeller guard for use in association with a boat propulsion propeller driven by an outboard motor or an inboard / outboard rear motor drive unit . the propeller guard may be constructed of injection molded plastic , fiber reinforced resin , metal such as aluminum or other materials having strength characteristics to provide necessary protection and constructed to minimize hydrodynamic resistance . the propeller guard will protect swimmers , aquatic mammals and other sea life from coming into contact with the propeller thereby preventing injury and at the same time protect the propeller from damage by engagement with floating or submerged debris .