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Precision Anchoring, Continued
Post Anchoring
After plotting the drag circle, the navigator then selects several lighted
Procedure,
NAVAIDs suitable for use in obtaining fixes by day or night and enters
continued
them in the bearing book for use by the anchor-bearing watch. The
anchor-bearing watch is charged with obtaining and recording in the
bearing book a round of bearings to the objects designated by the
navigator at least once every 15 minutes, and plotting the resulting fix
on the chart each time. Should any fix fall outside the drag circle,
another round of bearings is immediately obtained. If the second fix
also plots outside of the drag circle, the ship is considered to be
dragging anchor and all essential personnel are notified. In practice, if
the ship is to be anchored for any length of time, the navigator will
usually have the anchor watch cover the area of the chart containing the
drag circle with a sheet of semiclear plastic. This is done so the chart
will not be damaged by the repeated plotting and erasures of fixes
within the drag circle.
When a ship is dragging anchor, especially in high wind conditions,
there is often no unusual sensation of ship’s motion or other readily
apparent indication of the fact. The safety of the ship depends on the
ability of the anchor watch to accurately plot frequent fixes and to alert
all concerned if they begin to fall outside the drag circle. If conditions
warrant, the ship may have to get under way. As interim measures to be
taken while the ship is preparing to do this, more chain may be veered
to increase the total weight and catenary of chain in the water, and a
second anchor may be dropped if the ship is so equipped.
Situations in which high winds are forecast, the ship should assume an
increased degree of readiness, with a qualified conning officer stationed
on the bridge, and a skeleton engineering watch standing by to engage
the engines if necessary. As an example, during a Caribbean cruise a
U.S. Navy submarine was anchored off St. Thomas, V.I., in calm
waters with less than 5 knots of wind blowing. Because high winds had
been forecast for later in the night, the OOD was stationed on the
bridge, and a skeleton engineering watch was charged with keeping the
engines in a 5-minute standby condition. Two hours after anchoring,
after the liberty sections had gone ashore, the wind began to increase.
In the next 45 minutes, wind force increased to the point where 55-knot
gusts were being recorded.
The ship got under way and steamed
throughout the night until the storm abated the next day. For additional
information on anchoring, types of anchors, and anchoring gear, refer to
Naval Ships’ Technical Manual, chapter 581, titled "Anchors and
Anchoring."
12-20
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