Abstract: A method for the determination of in-line and cross-line components of water velocity relative to a vessel heading on a chosen line, which method comprises the steps of:(a) generating electronic pulses and relaying these to a Doppler-Sonar transducer aligned fore and aft with respect to the keel of the vessel,(b) radiating pulses from the Doppler-Sonar transducer in a number of directions at an angle .theta. relative to the horizontal to a layer of water below but near to the surface of the water, and, simultaneously,(c) radiating pulses from the Doppler-Sonar transducer in a number of directions at an angle .alpha. relative to the horizontal, and greater than .theta.