Depth Sounder (Echo Sounder)

The depth sounder can warn well in advance if the ship is getting too close to any shoal areas or closing with the coastline. The original depth sounder was a long line with a piece of lead on the end and a series of marks along its length which, when dropped to the sea bottom, measured the depth of water. This was used before Captain Cook's day and is still a useful addition to a ship's equipment where the navigator might have reservations about the reliability of electronics! Colour Video Sounder; Click for a larger Image [32 KB]

Most Echo Sounders measure the time interval by means of electronic circuits and produce a continuous record of the depth of water beneath the vessel in the form of a chart or graph.

The electronic depth sounder operates in a similar way to radar. A transducer in the bottom of the hull sends out an electronic pulse which echoes back from the seabed. The echo is timed electronically and transposed into a reading of the depth of water under the hull. Multi-colour displays in the monitor show not only the depth of the water, but different types of seabeds, prominent features such as sunken wrecks, and sometimes even schools of fish. The more advanced sounders can transmit the pulse ahead of the boat and thus indicate the approach of navigational hazards such as reefs or shoals in good time to avoid them. There are two main uses for the depth sounder in coastal navigation. The first, as described above, is to help locate the ship's position when used in conjunction with other electronic instruments. And secondly, to assist in navigation through shallow inshore passages and channels, or over bars. The most common External Controls found on Echo Sounders. Illumination Control. The illumination control provides continuous regulation of the illumination of the echogram and the front panel controls. The illumination lamps will extinguish when the recorder is switched off. Receiver Gain Control. This control regulates the amplification of the received signals. Correct setting: Turn the knob clockwise until a stable depth indication is obtained on the digital depth indicator. If the setting is too low the depth-indicator will start blinking. Too high setting may result in false depth indication from air bubbles, plankton layers, side lobes, etc. By turning the control fully anti-clockwise the echo-sounder is switched off. Range Selector. This control selects the basic ranges according to the table given under technical specifications. In position 0 the recorder is switched off and the depth will be shown only on the digital depth indicator. The depth warning and any remote depth indicators will be operational. Maintenance Cleaning Keep the cabinet clean and dry. If desired, the cabinet may be polished with a good car wax. Take care not to wax the acryl window and front plate. This should be cleaned with ordinary soap and wet cloth. The transducer normally needs little attention. However, the radiating face should be cleaned when docking. Use synthetic soap. Marine growth may be removed with a piece of wood, whereupon the radiating face is carefully cleaned with fine-grade sand paper or emery paper. The radiating face must not be painted!