2835 



HYDROGRAPHIC MANUAL 



Page 176 



it ise asier to engage and there is less likelihood of losing the larger screw pin. Because 

 buoys are in continual motion, the screw pin of every shackle used should be secured 

 by seizing wire through the shackle and the hole in the pin. 



The anchor cables of buoys used in shoal water and at places where the currents are not strong 

 may be attached directly to the eyebolt in the buoy structure. A ^i-inch swivel is shackled to the 

 chain (or wire rope) by a 5^-inch shackle, the other end of the swivel being shackled to the eyebolt 

 with a %-inch shackle. The same arrangement of a swivel and two shackles should be used to attach 

 the cable to the anchor. A buoy anchored in this fashion is sketched in A, figure 47. 



A sono-radio buoy is generally anchored with an intermediate buoy (relieving buoy) to support 

 the entire weight of the anchor cable in the prevailing current. Ordinary survey buoys are frequently 

 anchored in this fashion where strong currents are known or suspected to exist. All of the strain 

 of the anchor cable is on the relieving buoy which allows the survey buoy to float upright so that the 

 visibility will not be reduced. This general scheme is shown in B, figure 47. The relieving buoy is 

 a 55-gallon steel barrel around each end of which ^^-inch chain is fastened between the end and the 

 rolling tracks, drawn tight by connecting pieces of chain. The relieving buoy is connected to the 

 survey buoy by means of a 4-fathom length of chain using a swivel at the survey buoy and a shackle 

 or a ^8-inch lap link at the relieving buoy. A shackle and swivel assembly is used on each end of the 

 main anchor cable between the relieving buoy and the anchor. 



Discarded United States Navy buoyant mine casings m.2bj be obtained from junk 

 j^ards in some localities, for use as relieving buoys. These casings are pressed steel 

 spheres, 30 inches in diameter, with a swivel to which the anchor cable may be attached. 

 To adapt them for use as relieving buoys, a U-shaped stirrup, with a 1-inch eye in the 

 top, is welded to the side opposite the swivel. This stirrup may be made of ^g-inch cold- 

 rolled steel rod and made large enough (at least a 4- by 6-inch opening) so that it may 

 be readily engaged by a hook when weighing. 



The buoyancy of the unit may be increased by the arrangement shown in C, figure 47. A short 

 pendant of %-inch chain (about 1 or !){ fathoms) from the relieving buoy supports a ring to which 

 the anchor cable and the connecting chain between buoys are secured. The pendant allows the strain 

 of the anchor cable to be carried by both buoys. The length of the pendant chain should always be 

 somewhat shorter than the connecting chain so that the buoys will not be brought together. This 



arrangement should not be used on sono-radio buoys 

 because their heavier weight leaves little reserve buoy- 

 ancy available to carry the weight of the anchor cable. 

 Occasionally the anchor gear of a buoy must be 

 hoisted on board before the buoy itself, and when this 

 is necessary a substitute method of attaching the anchor 

 cable to the buoy structure, as illustrated in figure 48, 

 has been used to advantage. Three eyebolts are used 

 in the buoy structure, one above the waterline and two 

 spaced 2 inches apart at the position where the single 

 eyebolt is usually placed on the one-barrel buoy (see 

 2824 (A)). An iron rod, bent at right angles at one end, 

 passes through the three eyebolts and is of sufficient 

 length so that its lower end extends a few inches below 

 the lowest one. 



The upper end of the anchor cable is made with an 

 eye which is placed between the two lower eyebolts when 

 the rod is inserted, thus securing the anchor cable to the 

 buoy so that it can be easily and quickly detached. A 

 lanyard, of the same material as the anchor cable, is 

 spliced into the eye at the end of the anchor cable by 

 means of an eye splice. The lanyard is long enough to 

 extend above the waterline, and the upper end, in which 

 there is a large eye splice, is secured to the buoy structure 

 with a light lashing. After a hoisting line has been 



SCALE m FEET 



Figure 48. 



-Arrangement for a detachable buoy 

 anchor cable. 



