FATHOMETER, a device which is a practical development of the sonic or echo depth-finding principle for modern navigation purposes. This device is manufactured by the Submarine Signal Corporation in the United States, is a development of Prof. Fessenden's submarine oscillator, and produces a submarine sound, and detects the returning sound by electrical means. The fathom eter system consists essentially of three parts : a sound-producer attached to the skin of the ship; a sound-receiver located in a small tank of water, which tank is mounted on the inner surface of the skin of the ship; and the fathometer indicator, which con trols the despatch of the electrical impuises as sound waves, and converts the elapsed time of the resuaing echoes into visual indi cations of depth.
The relation between the sound-producer and the sound-receiver is comparatively simple. The sound is reflected back from the bottom of the ocean and strikes the plates of the ship. That sec tion of the plate supporting the tank which contains the sound receiver transmits the vibrations through the fresh water in the tank to the sound-receiver which converts the vibrations into elec trical waves. Wires running from the sound-receiver carry the electrical waves to the fathometer indicator, where they are shown as visual indications of depth. For soundings within the range required for ordinary navigation purposes, it is only necessary to glance at the dial of the fathometer as the soundings are shown by a flash of light that appears opposite a numeral on the dial. For soundings beyond the range usually required in navigation, a different method is used. The observer listens with head tele phones and notes the position of a revolving light when he hears the returning echo in the telephones.
The fathometer is started and stopped by means of a simple switch. Once started, the operation is entirely automatic, depth indications being given continuously. The apparatus contains no parts that require expert adjustment or careful maintenance. This method of taking soundings has many advantages over the older methods. For example, the soundings shown by a fathometer in dicate the depth directly beneath a vessel whether the vessel is proceeding or stopped; ordinary speeds have no effect whatever on the operation of the device. On the other hand, the older forms of sounding instruments requiring physical contact with the bottom, consume so much time in their operation that when the sounding is finally reported, the ship, if it has been moving, is far away from the spot, the depth of which is reported. Further more, the fathometer can be left in operation for indefinite periods of time resulting in thousands of soundings being indicated per hour. This feature of the device has led navigators to take lines of soundings when approaching objectives and to chart the sound ings for comparison with soundings shown on subsequent trips. Thus these navigators become so familiar with the soundings on their true course that they can check position readily by refer ence to soundings. Fathometers are in operation on practically every important class of vessel.