On September 4, 1979, US patent number 4166462 was issued for a self-propelled shark-proof cage;"Patent 4166462" www.patentstorm.us being designed to allow abalone divers to collect abalone without becoming vulnerable to attack. Thanks to the propulsion system, abalone divers would exert themselves less and, therefore, be able to collect their prey for longer periods of time. The patent abstract details a self-propelled cage with at least one access opening and a mounting frame that carries both an air motor and a propeller. Buoyant material is attached to the frame so that the cage may be made neutrally buoyant. This patent expired on September 4, 1996.
