Page 131 control and signal building 2546 



material that an excessive buoyancy is required to sustain its weight. The anchor 

 cables that have been used with success in the past are described in 283. 



Anchors should be of a type and weight to maintain their positions without drag- 

 ging against any strain of the anchor cable, but they should not be too heavy for ready 

 handling in anchoring and hoisting aboard. On good holding bottom, lighter anchors 

 may be used than on poor holding bottom. A small concentrated weight of high 

 specific gravity, such as a railroad car coupler, is to be preferred to a large bulky 

 concrete block. The couplers are more easily stowed on board ship and require less 

 space. The types of anchors that have been used with satisfactory results are dis- 

 cussed in 2831. 



2546. Buoy Usage 



When buoys are to be used for the control of an extensive hydrographic survey, 

 the work must be planned so that a section at a time can be completely surveyed and 

 fully developed as the control is carried forward. This requires a minimum total 

 number of buoys, a minimum number at anchor at one time, and the buoys are left 

 on their stations for only short periods before being brought on board where any damage 

 or deterioration can be detected and repaired. It is inadvisable to have a large number 

 of buoys at anchor to furnish control for a long period of time because of the risk of 

 the positions being lost by parting of the anchor cable from deterioration or during 

 severe storms. The limited space on board for stowage frequently limits the number 

 of buoy structures to those required for control in an area which can be surveyed in 

 about 2 weeks. The general plan should be to establish the control in an area which 

 can be expected to be completed during the period between trips to port. 



AMiere buoys are located by traverse, it is not necessary that the entire traverse 

 be completed, closed, and adjusted before the buoy positions are usable. This may 

 be done in sections, each section providing sufficient control for each trip in the field, 

 the preliminary unadjusted positions sufficing for plotting on the boat sheet. A 

 sufficient nimiber of buoys should be anchored and located at the beginning of a trip, 

 and at the end of the trip all those no longer needed for control or for the extension 

 of the traverse should be picked up and stowed on deck. This not only eliminates 

 the possibility of loss of buoys while the ship is in port, but also affords an opportunity 

 for repairs to the structures. If the progress of the survey is away from the base, 

 another advantage is that buoys may be anchored en route to the working ground 

 and weighed while en route to port. 



When R.A.R. control is used, the areas are generally too extensive to be com- 

 pleted in one trip but it should be possible to follow^ the same general plan, except 

 that the buoys are left in position for two trips in the field instead of only one. 



In general, buoys should not be left in the water for more than 6 weeks or 2 months 

 at a time. Salt water soon corrodes ordinary wire rope and, if left for a longer period, 

 the loss of the buoy and anchor is risked by parting of the wire. Wlien a buoy position 

 is required for longer periods, it should be referenced, at the end of 2 months, by anchor- 

 ing another buoy nearby, which is located by reference to the original (see 2531). The 

 new buoy position may then serve in lieu of the original position in the event that the 

 buoy at the latter is lost. 



wSono-radio buoys are generally visited more frequently than ordinary buoys, to 

 renew batteries and to service the R.A.R. units, and more opportunity is afforded to 

 inspect the condition of at least the upper part of the anchor cable. Because of its 



