Page 381 equipment and instruments 4542 



4542. Hydrographic Clocks 



In hydrographic surveying a stm-dy, accurate clock by which* to record the times 

 of positions and soundings is essential. Tide reducers, the spacing of soundings between 

 positions, the interval between soundings, and other events are all controlled by recorded 

 time. Accurate time is most important in areas having a large range of tide, such as 

 Alaska and New England. 



To be adequate a clock must be sturdily constructed to withstand hard usage, and 

 must be sprayproof. It 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 wall 

 mounting by means of screws. 



For portable use, especially in launch hydrography, it is most convenient to mount 

 the clock on the sloping front of a box about 12 inches high with a 10-inch square base. 

 The box should be provided with a handle for carrying. The front of the box should 

 slope about 30° from the vertical. Such a box provides a secure base for the clock and 

 affords it some protection. For additional,security, screw eyes may be screwed into 

 the sides of the box for use in lashing it to a bulkhead. Mounting a clock permanently 

 on a canopy or bulkhead, or using it unmounted, is not as satisfactory as the box 

 mounting. 



Hydrographic clocks must be compared and set to correct time before the start of 

 the day's hydrography and compared after its conclusion. When practicable, they 

 should be checked several times a day. When coordinated survey operations take 

 place in different parts of a ship the several clocks used for recording time must be kept 

 within a few seconds of agreement and must be compared with one another as fre- 

 quently as necessary to ensure this. (See also 6734.) 



Any hyth'ographic clock which cannot be adjusted to maintain correct time within 

 3 minutes per 24 hours should be returned to the Washington Office for repairs. 



The recorded times of soundings should generally be within 1 minute of correct 

 time, although this limitation may be exceeded for hydrographic parties based in camps 

 in remote places without provision for accurate time comparisons. 



4543. Sounding Interval Clock 



A hydrographic clock that will ring a bell or buzzer at certain selected intervals of 

 time has been designed by an officer of the Coast and Geodetic Survey. It is known 

 as the "Green Hydrographic Clock." The mechanism consists of contacts with which 

 the second hand makes an electric contact at intervals of 15, 20, 30, or 60 seconds. The 

 contacts are connected to a bell or buzzer, operated by electricity furnished by dry cell 

 batteries or by ship's current. The batteries, and also the bell and switch, if desired, 

 can be placed inside the box described in 4542. The box affords protection from the 

 weather and makes the whole a compact unit. Such a clock has the obvious advan- 

 tages of ensuring that the time intervals will be equal, of giving the recorder more time 

 for his other duties, and of lessening the possibility of a missed sounding or an erroneous 

 interval owing to the recorder's inattention to the clock. 



Besides its use as a hydrographic clock, it is of value when navigating in fog. The 

 clock can be set at the 60-second interval and the whistle blown at every buzz when 

 in Inland Waters and at every alternate buzz when International Rules apply. Other 

 uses will be found, whenever definite intervals of time are needed. 



