2834 HYDROGRAPHIC MANUAL PaGE 174 



conditions encountered, but in general the following should prove satisfactory for 

 buoys in the open ocean, except where unusually strong currents prevail: 



(1) In depths less than 15 fathoms. — A total length approximately three times the depth, composed 

 as follows: 



For ordinary buoys — three times the depth of ^^-inch boat chain. 



For sono-radio buoys — twice the depth plus 2 fathoms of %-inch boat chain, plus the depth minus 

 2 fathoms of wire rope. 



(2) In depths from 15 to 50 fathoms. — A total length that is approximately twice the depth, 

 composed of the depth plus 5 fathoms of ^^-inch boat chain, plus the depth minus 5 fathoms of wire 

 rope. 



(3) In depths from 50 to 200 fathoms. — A total length that is approximately one and one-half times 

 the depth, composed of one-half the depth plus 10 fathoms of 5i-inch boat chain, plus the depth 

 minus 10 fathoms of wire rojDe. 



(4) In depths greater than 200 fathoms. — A total length that is approximately the depth plus 100 

 fathoms, composed of 110 fathoms of %-inch boat chain, plus the depth minus 10 fathoms of wire 

 rope. 



When a buoy is to be used for only a short period of time or when it is anchored 

 in an area where exceptionally good weather conditions prevail or in protected places, 

 shorter lengths of anchor cable may be used. 



A proportionately longer anchor cable must be used in shoal water because heavy 

 surges are likely to cause the anchor to drag, but in deep water the greater weight of 

 the suspended cable dampens this effect. For deeper water enough chain should 

 be used adjacent to the anchor so that the wire rope will touch neither the bottom 

 nor the anchor at any time. Continual dragging over the bottom soon abrades the 

 wire rope excessively and it is likely to become kinked if allowed to come in contact 

 with and wrap around the anchor. 



2834. Parhhurst Anchor-Detaching Apparatus 



Considerable time is required and the hoisting equipment is subjected to excessive 

 strain in weighing buoy anchors from depths of a thousand fathoms or more. There 

 is also the danger of parting and losing the anchor cable. It is frequently more eco- 

 nomic to detach and leave on the bottom the inexpensive anchor to ensure the rapid 

 and certain recovery of the more expensive stainless steel anchor cable. To effect 

 this an anchor-detaching apparatus has been designed consisting of three parts; a cone- 

 shaped clamp, a detaching housing, and a heavy messenger. These can be requisi- 

 tioned from the Washington Office. 



The brass cone-shaped clamp, 4 inches long and 2 inches in diameter, consists of two halves 

 between which the wire rope lies in a lengthwise hole of small diameter. The halves are bolted to- 

 gether around the wire by four stud bolts in a recessed section of the cone. The clamp is attached, 

 pointed end uppermost, to the lower end of the wire rope which is to be retrieved. 



The detaching housing of cast brass is projectile-shaped, 11 inches long by 2% inches in diameter, 

 and it too is constructed in two halves, called fingers. The two fingers are pinned together at the 

 lower square end by a half-inch diameter hinge pin, which also passes through the end link of the anchor 

 chain, which is to be left on the bottom. The interior of the upper tapered end of the housing is 

 machined to fit the cone-shaped clamp. The fingers are held firmly together around the clamp by a 

 fixed cross pin into a hole in which a trigger pin is inserted through a longitudinal hole in one of the 

 fingers. The trigger pin is held in place by a lead shear pin. The trigger is formed by the lower end 

 of the trigger pin being bent at right angles to extend well outside the housing, where it will be struck 

 by the messenger on its downward trip as it passes over the housing. 



The messenger is a 50-pound oval-shaped iron weight cast in two halves, which are hinged on 

 one side and may be clamped together on the other side by two toggle-type trunk clasps. When 

 clamped, it has a hole through the center about 3 inches in diameter, through which the housing can 

 pass easily. 



