Electronic shut off systems

An electrical control system for suddenly stopping a propeller in a motor driven watercraft, comprising at least one piezoelectric transmitter, at least two piezoelectric detectors and a control circuit that can stop or slow the propeller to less than 10 rpm within one second, wherein one or more of the detectors can detect a signal from the transmitter and triggers the control circuit upon sensing the object.

An electrical control system for suddenly stopping or slowing a propeller in a motor driven watercraft, comprising at least one sensor that detects an object near the propeller, a control circuit that can stop or slow the propeller to less than 10 rpm within one second, and a magnetic particle brake or clutch, wherein the at least one sensor triggers the control circuit upon sensing the object, and the control circuit electrically activates the magnetic particle brake or clutch to affect sudden stopping, or slowing of the propeller.

A system for monitoring boat speed of a controlled waterway, comprising:

• a) one or more fixed position transmitters that emit energy into or over the waterway;
• b) a movable receiver that may be carried in or attached to a boat that can transit the waterway;
• wherein the receiver can monitor the boat speed and can report the speed to a fixed position receiver and thereby reporting violations of speed limit.