Page 173 control and signal building 2833 



cable is composed of half-inch wire rope with a section of chain near the anchor. For 

 greater depths %-inch wire rope is used, the buoy containmg sufficient barrels to suspend 

 it (see 2833). 



For anchoring in extreme depths (500 fathoms and more) stainless steel wire rope 

 of smaller diameter has recently been used with gratifying results. The sizes of com- 

 mercially manufactured stainless steel wire rope recommended for this purpose are 

 %&- and }^-inch diameters in both 7 by 7 and 7 by 19 construction; the 7 by 7 is less 

 flexible but more durable than the 7 by 19. The stainless steel wne rope is stronger 

 and more durable than ordinary galvanized steel wire rope of comparable size, and costs 

 approximately three times as much. The higher cost is warranted to prevent loss of 

 buoys because of anchor cable failure, but aside from this the exclusive use of stainless 

 steel rope may be actually more economic because of its more durable qualities and 

 its resistance to corrosion. The life of ordinary wire rope, when constantly exposed 

 to sea water, is seldom more than one season (6 months), but stainless steel rope will 

 probably prove to have a usable life of several years. 



Galvanized iron used in conjunction with stainless steel rope in sea water is likely 

 to corrode seriously if immersed much longer than 1 month. Du'cct contact between 

 the two, sets up an active electrolytic action which removes the zinc and corrodes the 

 metal, the effect decreasing as the distance between the two increases. Stainless steel 

 thimbles and shackles are available for use with stainless steel rope and annealed 

 stainless steel wire should be used to serve all splices in such rope. Connections between 

 stainless steel rope and galvanized chain or other fixtures should be made with stainless 

 steel shackles and the galvanized parts protected with a coating of asphaltum paint. 



A survey party in the Gulf of Mexico in 1941 successfully used ordinary iron fittings 

 with stainless steel rope in short sections of 20 to 30 fathoms in shoal water, but when 

 these same fittings were used with long sections of 200 fathoms or more in deep water 

 they corroded rapidly. The reason for this is not apparent. 



Experiments have been conducted recently with buoys in currents to determine the 

 appropriate size of wire rope and chain and the reserve buoyancy required to prevent 

 the buoy from being towed under. These experiments indicate that the horizontal 

 force exerted by a current of 1 knot on the anchor cable of one bare 55-gallon barrel 

 80 percent submerged, is about 11 pounds, with the force varying directly as the 

 square of the current in knots (i.e., a 2-knot current will exert a 45-pound horizontal 

 force on the anchor cable). With two bare 55-gallon barrels in tandem the force on 

 the anchor cable is about doubled. These tests proved that the types and sizes of 

 wire rope and chain recommended above are sufficiently strong for any expectable 

 conditions. 



2833. Lengths of Anchor Cable 



In order that the scope of a buoy and the variation in its position be at a minimum, 

 the total length of the anchor cable should be the minimum that will be sufficient to 

 maintain it in position. The holding quality of the bottom is an important factor. 

 The buoyancy of the buoy also enters into the calculation because it may be towed 

 under in a strong current, if a minimum of cable is used and the buoyancy is insufficient. 

 If the buoyancy is sufficient but the cable is not long enough, the buoy may drag its 

 anchor if the horizontal strain on it is great enough. 



Specffic rules for lengths of cable cannot be laid down because of the wide variety of 



