88 



HYDROGRAPHIC MANUAL 



the wire should be replaced being careful to 

 follow the original pattern exactly. 



All connections should be examined to see 

 that there is good contact and that they are 

 firmly made. A further check on connections 

 for magnetostriction transducers can be 

 made with a low-range wheatstone bridge. 

 The average resistance of the wiring in these 

 units is less than 0.1 ohm. The overall re- 

 sistance of the transducer and the cable leads 

 to the recorder should be measured and re- 

 corded. This measurement should be checked 

 periodically. An increase in the resistance 

 is an indication that the connections should 

 be re-examined. 



The transducers mounted in the hulls of 

 Coast and Geodetic Survey ships are usually 

 exposed directly to the water and not painted. 

 When a ship is hauled out, the exposed sur- 

 faces of the sonic projector units are cleaned 

 while still damp using non-metallic, non-ab- 

 rasive brushes so as not to mar the polished 

 surfaces or rubber diaphragms. A metallic 

 face is then swabbed with a solution of 1 

 part nitric acid to 5 parts of fresh water, 

 washed with soapy water, and flushed with 

 fresh water. If necessary, the surface is then 

 polished with crocus cloth. Rubber faces are 

 cleaned with mineral spirits, or fingerprint 

 remover, and washed with fresh water. 

 Detergents are never used to clean rubber 

 units. 



After being cleaned, the projectors are 

 covered with a protective mask which is re- 

 moved just before undocking. Metallic trans- 

 ducer faces are never painted. On ships op- 

 erating in tropical waters or other areas 

 where underwater fouling is rapid, rubber 

 faces may be painted with a special anti-foul- 

 ing paint procured from the Navy. The paint 

 is described in specification MIL-P-15152A. 

 The Navy stock number is G 8010-286-3177. 



3-108 Installation of echo sounders. — 



Specific details of echo sounder installations 

 are as varied as the number and kind of 

 vessels used. There are some general con- 

 siderations which apply in all cases. 



(a) Ship Installations. — The recording 

 part of the equipment is mounted against 

 a bulkhead, or on a specially constructed 



mounting, in the bridge area. All echo 

 sounders to be used in hydrographic sur- 

 veys should be located in the same general 

 area (Fig. 28). The space should be well 

 ventilated and adequately lighted. The hy- 

 drographic team should be stationed so that 

 they may communicate with each other with- 

 out raising their voices above the level of 

 normal conversation. 



The transducers are mounted in the hull 

 at a point somewhat forward of midships — 

 preferably immediately below the center of 

 position fixing operations. All transducer in- 

 stallations on ships are made in accordance 

 with plans and specifications drawn or ap- 

 proved by the Vessels and Equipment Branch. 



(b) Launch Installations. — Portable echo 

 sounders are mounted in launches at an angle 

 of about 30" with the horizontal and in such 

 a manner that they are easily accessible for 

 servicing. Because of the high noise level in 

 most launches, the echo sounder operator, the 

 recorder, and plotter should be positioned 

 close to each other (Fig. 29). A well-lighted 

 cabin is essential to reduce eye strain for 

 all members of the party. 



The basic electrical power in most hydro- 

 graphic launches is a 150 ampere hour 12- 

 volt battery. A typical system consists of 

 two 12-volt batteries and a generator belt 

 driven by the launch engine. On some ships 

 the launches are not equipped with genera- 



FlGURE 28. — Echo sounders installed on an ocean 

 survey ship. 



