A biaxial propeller current-meter system for use in shallow water, where instrumentation can be attached to rigid bottom-mounted towers, has been developed at the Chesapeake Bay Institute. The use of two like sensors to measure the horizontal-velocity vector eliminates the problem of matching time constants in rotor-vane systems. The propellers have a noncosine response to the angle of attack of the flow. However, the data recorded by two propellers mounted at right angles are sufficient to correct for the noncosine response.
Cannon, Glenn A., and Donald W. Pritchard. 1971. "A biaxial propeller current-meter system for fixed-mount applications." Journal of Marine Research 29, (2). https://elischolar.library.yale.edu/journal_of_marine_research/1211