A safety system, which stops the motion of a sail boat when a person falls off the boat, is comprised of a wireless transmitter carried by the person, a receiver-controller, an actuator, and a separable member which ordinarily holds a sail or a sail assembly in its working position. When the person falls off the boat and or the boat moves away, the diminution in wireless signal causes the actuator to separate the connecting member which holds sail in place, thus reducing the propulsive power and altering the motion of the boat. A preferred actuator stores manually input energy, to enable the use of a compact and low power solenoid type coil.