Wire Soundings

Since the introduction of sonic methods, relatively few wire soundings are taken for the sole purpose of measuring depths. Checks must be made from time to time to see that the sonic equipment is operating successfully, but in most cases wire soundings are now made for the express purpose of obtaining samples of the sea-bottom sediments. The weight of equipment used for collecting bottom samples has increased, and, as a consequence, the piano-wire sounding machines are no longer

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adequate. Instead, the hydrographic cable and winch, or even the heavy winch, must be used for this purpose. The amount of weight attached to the end of the wire rope or mounted on the bottom-sampling device depends upon the strength of the cable, the depth of water (hence, the weight of wire suspended in the water), and in many cases upon the type of sampling device. It must be sufficient, when the weight itself reaches the bottom, to permit the detection of the reduced load by means of the motion of the accumulator, dynamometer, or other device. Unless the winch is stopped immediately, the wire rope will pile up on the bottom and will be badly tangled or kinked when hauled in again. If iron weights are used, they may be dropped by a release mechanism when striking the bottom, but, if lead weights are used, they are permanently secured. For sounding with 5/32-inch steel rope, about 50 lb must be attached to the end of the cable for depths less than 1000 m, and for depths of about 4000 m, double the amount of lead is needed.

An unprotected reversing thermometer for measuring pressure, used in conjunction with a protected reversing thermometer and attached to the sounding wire some 50 m above the weight, is sometimes used as a check on the depth (p. 351).