Abstract: A method and system for measuring relative speed of a ship through a body of water with improved accuracy and simplicity. It employs a free floating buoy and a pair of tracking scopes. The buoy is launched and tracked by the scopes with electronic circuit arrangements so that the time of relative movement of the buoy between transverse positions opposite the scopes is accurately measured.

Abstract: A single scope method or system for accurate ship speed measurement relative to the water through which it is propelled. There is a free floating buoy beside the ship, and a tracking scope is trained on the buoy. At the same time the height above the water of the scope is measured in addition to the negative elevation and the azimuth angle of the line of sight of the scope relative to the ship. Periodic calculations with time measurements determines the speed of relative movement of the buoy along a path parallel to the center line of the ship. This is the ships speed relative to the water. Calculations may be made by a microprocessor with the measured angles and height above the water as inputs.