90 



HYDROGRAPHIC MANUAL 



than 30 feet, it should be at least 9 inches 

 wide. 



When an 808 type echo sounder is used, 

 one of the transducers used for sounding can 

 be disconnected and another standard unit 

 connected in its place. The latter unit is sus- 

 pended by a marked wire and cable lead and 

 the distance between the units will be re- 

 corded on the graph. The suspended unit 

 must be directly below the sounding unit, 

 or appropriate corrections applied for any 

 offset. The sound travels only one way, from 

 one unit to the other, and no echo is in- 

 volved, therefore the recorded depth must be 

 doubled to obtain the true depth. 



The supporting lines should be of wire or 

 have wire cores, like the material used for 

 leadlines. The lines shall be carefully marked 

 and their lengths verified in accordance with 

 instructions for the leadline (see 3-65 and 

 5-54). 



3-110 Hydrographic clocks. — All the var- 

 ious events of hydrographic surveying must 

 be correctly associated in time (see 5-95). 

 Tide reducers, the interval between sound- 

 ings and positions, and other operations are 

 controlled by time. In EPI controlled sur- 

 veys the shore stations and the ship, or 

 ships, must use accurately coordinated clocks 

 to govern positioning operations. Time is 

 also very important when surveys are made 

 in areas having a large range of tide. 



On ships equipped with EDO-185 echo 

 sounders, an electric clock should be included 

 in the 60-cycle controlled frequency circuit 

 to provide very accurate time. Electrical 

 contacts for sounding a buzzer or bell at 

 various intervals of time can be attached to 

 the clock. 



For portable use, especially in launch hy- 

 drography, it is most convenient to mount a 

 clock on the sloping face of a box about 12 

 inches high with a 10-inch square base. The 

 front of the box should slope at an angle of 

 about 30°. The clock should be of the 8-day 

 type with an easily read 6-inch dial and 

 should be enclosed in a transparent-faced, 

 nickel-plated case, arranged for mounting by 

 means of screws through holes in the base 

 flange. The clock should be sturdily con- 



structed to stand hard usage and should be 

 spray proof. 



A hydrographic clock that will sound a 

 buzzer at selected intervals is available and 

 shall be used by launch hydrographic parties. 

 A mechanism is attached to the clock and 

 consists of contacts with which the second 

 hand makes an electrical contact at intervals 

 of 10, 15, 20, 30 or 60 seconds. The contacts 

 are connected to the buzzer and power is 

 furnished by dry cell batteries placed inside 

 the box. Such a clock has the advantage of 

 ensuring uniformity of sounding intervals 

 and of giving the recorder more time for his 

 other duties. 



Clocks should be adjusted to keep time 

 correctly, and any clock which cannot be 

 adjusted to maintain correct time within 3 

 minutes per 24 hours should be repaired lo- 

 cally or returned to the Washington Office. 

 Hydrographic clocks should be compared with 

 a standard and set correctly at the start of 

 each day's work and compared again at the 

 end of the day. Camp parties should make 

 comparisons with the standard by radio at 

 least once each day. 



Oceanographic Equipment 



3-111 Oceanographic winch. — Before the 

 advent of echo sounders, ocean depths were 

 sounded by making vertical casts with piano 

 wire. Because of the low breaking strength 

 of the wire, a detachable weight was used. 

 Oceanographic observations with the wire 

 sounding machine were time-consuming and 

 limited by the size of wire ; however, observa- 

 tions were made with this type of machine 

 in depths of 4,600 fathoms. 



A winch of some type for making casts 

 to considerable depths is an essential item of 

 equipment for survey ships of all sizes. 

 Oceanographic instruments have become 

 larger and heavier creating a requirement 

 for winches of greater lifting capability. 

 Several expedients have been used in adapt- 

 ing various types of available winches to 

 oceanographic work. These have included di- 

 rect current electric drive motors and both 

 direct and alternating electro-hydraulic drive. 

 Because of the fine degree of control required 



