Abstract: Echo sounding apparatus mounted on a boat (52) comprises a transducer unit (1) connected to a display device (2) which contains a control and processing circuit (53) via a cable (3). Sound pulses reflected from features below the keel and in front of the bow of the boat (52) are processed to generate first and second location signals. The first location signal defines an unambiguous feature position with low angular accuracy. The second location signal defines possible feature positions with high angular accuracy. The first and second location signals are combined to define an unambiguous feature position with high angular accuracy. The results are displayed in a vertical cross section of features and water in the correct positions relative to a scale picture (10) of the boat (52).