3422 HYDROGRAPHIC MANUAL PaGE 256 



With the whe-core tiller rope now used for leadlines there is less likelihood of an 

 appreciable error in the length of the line than there used to be. However, each lead- 

 line used must be compared with standard marks before and after each day's sounding 

 and the results noted in the Sounding Record (see 4622). If errors are found in the 

 length of the leadline the recorded soundings must be corrected for them when reduced 



(see 8221). 



3422. Wire Sounding 



To obtain a vertical wire sounding the ship or launch must be stopped while the 

 wire is running out. In lesser depths the lead should not be released until the vessel is 

 stationary in the water; in greater depths it may be released while the vessel has a 

 slight headway. During the descent of the lead the vessel is maneuvered to keep the 

 wire vertical until the lead strikes the bottom. In sounding from a launch, the launch 

 proceeds ahead as soon as bottom has been reached and while the wire is being reeled 

 in. In greater depths sounded .from the ship the wire must be reeled in to within a few 

 hundred fathoms of the surface before going ahead. 



From a launch the wire should not be allowed to run out at a rate exceeding 100 

 fathoms per minute. From a ship it can be payed out at rates up to 150 fathoms per 

 minute for about the first 1,500 fathoms, at rates not to exceed 100 fathoms per minute 

 for the second 1,500 fathoms, and in greater depths at a rate not exceeding about 50 

 fathoms per minute. At rates faster than these there will be danger of the wire jumping 

 off the reel during the descent or when the lead strikes the bottom. When sounding in 

 rough weather these rates must be decreased. The wire should never be reeled in at 

 a rate faster than 100 fathoms per minute. 



Considerable skill and experience are required to operate the sounding machine, 

 especially in letting the wire run out and in braking when the lead strikes bottom so 

 that the wire will not jump off the reel and become entangled around the drum and 

 shaft. For use in such accidents a stopper should always be kept available which can 

 be attached to the wire to take the weight of the wire and lead while the snarled wire 

 is being cleared. In extreme cases it is necessary to cut the wire to clear it, making a 

 temporary splice in order to heave in the lead. When sounding in rocky bottom and in 

 rough weather, particularly from a launch, it is almost inevitable that the wire will be 

 parted occasionally and the lead lost. A supply of spare leads should always be kept 

 on hand. 



In great depths, and when the sea is rough, it is often difficult to detect when the 

 lead strikes bottom. If the wire is allowed to continue to run out after the lead strikes 

 bottom, the wire is likely to kink and may then part when it is reeled in. 



On modern survey ships, sounding machines are installed on the bridge deck with 

 the wire led outboard to a fair-lead at the end of a boom (see 4633). When soundings 

 are taken with such an installation the ship can maneuver at will to keep the sounding 

 wire vertical. To obtain a deep sounding the ship should be hove-to, headed into the 

 wind, with the wind slightly on the bow over which the sounding wire leads. This 

 will ensure, if the ship falls off the wind, that the wire will not lead under the ship's 

 bottom. With a twin-screw vessel no difficulty will be encountered in keeping the 

 wire vertical. More skill is required with a single-screw vessel, but better results will 

 be obtained by keeping the vessel heading nearly into the wind at all times. 



In addition to leeway there will often be surface currents which will affect the 

 position of the ship but will not influence the lead after it has descended a few hundred 

 fathoms. In such cases the ship may have to steam ahead continuously into the current 

 01- wind to keep the wire vertical. If, in spite of the care which is taken, the wire leads 



