TIDAL CURRENT METER

PURPOSE:To determine an accurate tidal current speed by using to-the-ground speed, the latitude and angle of the advancing course to the latitude direction which are sensed by a navigation device, and correcting the sensed value with the azimuth error as determined from a specific formula. CONSTITUTION:To-the-ground speed, advancing course, and ship position data are determined by a position measuring device 1, and therefrom the azimuth error of a gyro compass 3 is calculated by an azimuth error calculation part 2. An azimuth correction part 4 corrects the azimuth sensed by the compass 3 with the obtained azimuth error, to output an accurate azimuth. A to-the-ground and to-the-water calculation part 5 determines the to-the-ground and to-the-ground speed from the corrected azimuth and the Doppler shift amount of echoes from the sea bottom and under the water which were sensed by an ultrasonic vibrator S. A tidal current calculation part 7 determines the tidal current speed from the to-the-ground and to-the-ground speeds. The azimuth error calculation part 2 determines beta from the equation beta= tan{Vs.sina/(Vs.cosa+900.coslambda)}, wherein Vs is to-the-ground speed, alpha is angle of advancing course, and lambda is latitude of ship position which are sensed by device 1. The azimuth sensed by the gyro compass is corrected with the obtained beta as azimuth error.