40 MANUAL OF CURRENT OBSERVATIONS 
three knots, the meter may be hung free from the buoy without the use of a leader. 
Observations are made at a single depth, which is usually 15 feet below the water 
surface. The weight of the anchor and the amount of chain and cable to be used will 
depend upon the depth of water at the proposed location of the current station and the 
velocity of the current. The minimum lengths of cable required for anchoring in various 
depths and current velocities are shown on Figures 22 and 23. These figures should be 
studied and understood before attempting to anchor the buoy. The anchoring equip- 
ment and meter are secured to the buoy and arranged on deck so that there will be 
no fouling of the gear as the mooring cable is payed out. 
106. The vessel is maneuvered into position so that the buoy anchor will be ready 
to drop on the selected location. The buoy is placed in the water and released from 
the boom cable. The cable is payed out as the buoy clears the vessel which is backed 
slowly if necessary. In backing extreme care must be observed not to upset the buoy. 
With buoy streamed and clear and no slack in the cable, the anchor is dropped in the 
selected location. After the buoy is anchored, its exact position must be determined 
by the methods described in paragraph 100. All bearings, angles or other observations 
used in determining the buoy position must be recorded and included in the current 
record book (Form 270) for that station. The position of the buoy anchor is the 
location of the current station. : 
107. As soon as a buoy is anchored and streamed into the current, test observa- 
tions are secured with receiving equipment to make sure that the station is operating 
satisfactorily. Thereafter, the velocity and direction of the current are recorded half 
hourly by radio receiving equipment and chronograph which may be on a vessel or at 
a shore station. The chronograph tapes should be processed at the receiving station 
after each half-hourly observation. The velocity and direction are determined as 
explained in paragraph 85. The velocity in knots and tenths and the true direction 
in degrees reckoned clockwise from north are tabulated in a copy of Form 270. This 
copy of form 270 must contain all the data called for in paragraphs 111-113 with the 
exceptions of the items that obviously are inapplicable to the measurement of currents 
by the radio current meter. 
108. Recovering the buoy.—For recovering the buoy a time is selected when the 
current is weak. The vessel slowly approaches the buoy against the current. As 
the vessel arrives alongside the buoy, the buoy is caught with a boat hook, secured to a 
block and raised from the water. The slack in the buoy anchor cable is hauled in by 
hand and secured to a bitt. The buoy is detached from the cable and attached to a 
line leading over the bow to the windlass. The meter is detached from the buoy and 
the buoy secured on deck. During this operation it is important that the ship put no 
strain on the buoy anchor particularly during the early stages of the operation before 
the cable is detached from the buoy. In a modification of the recovering procedure, 
the buoy anchor cable, rather than the buoy, is caught with a boat hook and a loop 
of the cable with adjacent slack hauled on deck and made fast. Then the cable is 
detached from the buoy, the buoy raised, the meter detached, buoy and meter secured 
and anchor cable and anchor hauled aboard with the windlass. 
109. A spherical relieving buoy has been used successfully in conjunction with the 
radio current buoy in the following manner. The buoy was anchored in a depth of 
30 fathoms. One end of a 30-fathom, 3-inch manila line was attached to a spherical 
buoy and the other end to the buoy anchor cable at a position 15 fathoms below the 
buoy. A 4-foot piece of 2-inch by 4-inch timber was made fast to the manila line at 
the end attached to the cable. This piece of timber was inserted to prevent winding 
