this invention relates to a marine safety apparatus for preventing accidents in small watercraft . the device interrupts the watercraft power plant when the watercraft operator is displaced from the operator &# 39 ; s seat . the principal aspect of the disclosure is an air bladder seat cushion connected to an air pressure actuated electrical switch . the pressure from the weight of a seated operator &# 39 ; s body is transmitted to actuate the switch between &# 34 ; on &# 34 ; and &# 34 ; off &# 34 ;, according as to whether the operator is seated or not . the switch in turn actuates or de - actuates engine operation , normally by interruption of an ignition system . an additional feature is provided to override the foregoing safety system , at low speeds . also a pneumatic delay is disclosed whereby circuit interruption is delayed slightly after seat lift - off of the operator , to preclude engine stop due to momentary lift - offs upon encountering minor water turbulence .