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Precision Anchoring, Continued
Executing the
Anchorage
When executing the actual anchorage, the navigator’s dual objective is to
keep the ship as near as possible on its preplanned approach track and to
have all headway off the ship when the hawsepipe is directly over the
center of the anchorage. As mentioned above, the navigator obtains
frequent fixes as the ship proceeds along its track, and keeps the bridge
continually informed as to the position of the ship in relation to the track
and the letting-go circle. The navigator recommends courses to get back
onto track if necessary. Since every ship has its own handling
characteristics, speeds that should be ordered as the ship proceeds along
the track are difficult to specify. In general, however, with 1,000 yards
to go, most ships usually slow to a speed of 5 to 7 knots. Depending on
wind and current, engines should be stopped when about 300 yards from
the letting-go circle, and the anchor detail should be instructed to "stand
by." As the vessel draws near the drop circle, engines are normally
reversed so as to have all remaining headway off the ship as it passes
over the letting-go circle. When the pelorus is exactly at the letting-go
bearing, the word "Let go the anchor" is passed to the anchor detail, and
the anchor is dropped.
As the anchor is let go, the navigator should immediately call for a
round of bearings to be taken, and he or she should record the ship’s
head. After the resulting fix is plotted, a line is extended from it in the
direction of the ship’s head, and the hawsepipe to pelorus distance is
laid off along the line, thus plotting the position of the anchor at the
moment that it was let go. If all has gone well, the anchor should have
been placed within 50 yards of the center of the anchorage.
Post Anchoring
After the anchor has been let go, the chain is let out or "veered" until a
Procedure
length or "scope" of chain 5 to 7 times the depth of water is reached.
At this point, the chain is secured and the engines are backed, causing
the flukes of the anchor to dig into the bottom, thereby "setting" the
anchor.
When the navigator receives the word that the chain has been let out to
its full precomputed length and that the anchor appears to be holding
round of bearings and the ship’s head, as well as the direction in which
the chain is tending. With this information, the navigator plots another
fix and recomputes the position of the anchor by laying off the sum of
the hawsepipe to pelorus distance plus the scope of chain in the
direction in which the chain is tending. This second calculation of the
position of the anchor is necessary because it may have been dragged
some distance from its initial position during the process of setting the
anchor.
12-18
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