Speed measuring and compensation apparatus for jet-propelled watercraft

Abstract

A speed measuring system for a jet-propelled watercraft which includes a pitot tube mounted within the jet intake chamber of the watercraft for measuring the dynamic water pressure therewithin. The pitot tube is linked via flexible tubing to a pressure port in the dashboard of the watercraft, which is fitted with an electronic pressure sensor. The output of the electronic pressure sensor is amplified and input to an analog-to-digital converter, where the digital data is then input to a microprocessor for calculation of the actual water speed as a function of the dynamic water pressure measured within the jet intake chamber of the watercraft. A variable linear scaling factor is applied to the digital pressure signal over different ranges of such signals to compensate for nonlinearities that are introduced in the dynamic water pressure within the intake chamber. Further adjustment of the digital pressure signal is made to account for static pressure variances caused by changes in altitude, barometric pressure, and the depth of the pitot tube sensor under the surface of the water. Pressure signal drop-outs caused when the jet intake opening breaks contact with the water are identified through signal processing and replaced with a substitute signal that is determined through a process of interpolation of prior pressure signals, to eliminate wide fluctuations in watercraft speed measurement.