10 to 50 min. Statistics from this sample population are an average time of
30 min, median time of 30 min, and a mode of 20 min. One anchor-handling
event was not included in the sample population. On 13 June the dredge was
being repositioned when the partially lowered dustpan became snagged on the
starboard bow anchor wire and it took 1 hr 20 min to clear. This solitary event
was excluded due to its nonrepresentative nature. During the entire demonstra-
tion time span of 192 hr, time logged for handling anchors (4 hr 50 min) was
2.5 percent of that total. During the last five demonstration days (after relocating
to Reach 2) when dredging operations were more routine, the anchor-handling
time (2 hr 5 min) was reduced to 1.8 percent of the total 117 hr available.
Passing vessel delays
Dredging delays caused by passing vessels depended on the passing vessel
types, sizes, numbers, travel directions, and dredge position in the channel rela-
tive to the passing traffic. During the first few days, the operating procedures for
when a vessel passed Beachbuilder evolved as experience was gained. During
this initial period, the dredge was primarily working on the RDB side of the
channel and was stopping and moving for any significant-sized vessel traffic.
CL stationing and ranges were used in the daily dredge reports to record
dredge positions; therefore, most future dredge position descriptions in this report
will be also be described in these terms (e.g., Sta 18+50, Range 255). Stations are
distances along the channel CL. Ranges, or offset coordinates, are lateral
distances from the channel CL and carry plus/minus coordinate values. MVN
ranges (or offsets) are positive to the right of the channel CL (and negative to the
left of CL) looking toward increasing stationing (or downstream). For example,
with the 700-ft-wide channel at HOP, a range of 0 (R 0) will lay right on the
channel CL, R 375 is on the RDB side toe of the channel, and an R -375 lies on
the LDB channel toe (see Figure 8).
On 8 June the dredge was operating around R 335, or close to the RDB toe of
the channel. For deeper draft vessels passing (with the concurrence of the pilots
on the dredge and passing vessel), the dredge would drop the cross-channel wire
to the bottom and continue dredging as the vessel passed. For shallower draft
vessels (approximately 15 ft and less) the Beachbuilder's pilot would usually ask
the passing vessel to steer to the negative range side of the channel (LDB side)
and the cross-channel anchor wire would not be slackened as the vessel passed
over the wire.
On 9 June the dredge started to work on the channel CL (R0). After starting
to dredge on Sta 60+00 R 0 at 1355, the dredge continued working until 1524
(total dredging time of 1 hr 29 min) when it was moved to Sta 53+00 R 365
because of vessel traffic. After consultation with the pilot who estimated when
the next deep-draft vessel would pass, it was decided to continue dredging at
Sta 52+30 R 365 to be able to optimize dredging time as opposed to having a
short time to dredge before the next deep-draft vessel passed. At 1600, after the
deep-draft vessel passed, the dredge was moved back out to Sta 53+00 R 0,
where it dredged until 1640 (total dredging time of 40 min) when it was moved
again back to Sta 52+80 R 365 for the next deep-draft vessel passing.
25
Chapter 4
Dredging Operational Characteristics Analyses
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