Patented Shark Cage
On 4 September 1979, US patent number 4166462 was issued for a self-propelled shark proof cage. The cage was designed to allow abalone divers to collect abalone without becoming vulnerable to attacks by sharks. With the propulsion system, the 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 propeller mounting frame that carries both an air motor and a propeller. Buoyant objects are attached to the frame so that the cage may be made approximately the same density as saltwater.