Method and mode of materials placement

waiting in the area may be an option. Detailed evaluation of the flexible-

discharge dustpan dredge mobility capabilities for sailing between dredging

regions is beyond the scope of this demonstration report.

Method and mode of materials placement

Under this factor, the dredging plant should be versatile enough to perform in

both open water placement and shore placement. As discussed above, the

Beachbuilder demonstrated a capability to conduct shore placement in a rela-

tively long pumping distance mode. Open water (overboard) placement was not

demonstrated during the demonstration.

Minimum-acceptable dredging rate per day

The controlling minimum dredging rates under this factor in the MVN report

for overboard and long distance pumping are 78,000 and 24,000 cu yd/day,

respectively. The overboard pumping configuration was not tested during the

demonstration. With respect to long distance pumping, the Beachbuilder

achieved an approximate average production rate of 27,800 cu yd/day pumping

222,100 cu yd (with pumping distances ranging from 6,550 ft to 10,820 ft) in

192 hr. The Beachbuilder pumped 10,000 ft or greater for approximately six out

of the eight demonstration days while working primarily on the RDB side of the

channel.

Capability for yielding to vessel passage

In the MVN report, the time projected for the dredge to yield to passing

vessels under this factor is 15 to 30 min. The HOP project demonstrated that

dredge downtime for vessel traffic is primarily a function of dredge position in

the channel, number of vessels passing, speed and direction of vessels passing,

and movement time required to allow safe passing clearance. The Beachbuilder

was able to continue dredging in the portion of the channel adjacent to the hard

point and submerged line with no downtime during passage of a single vessel by

dropping the cross-channel cable and raising it after vessel passage. Forward

movement into the cut was maintained during this period by the push tug. When

dredging on the far side of the channel, the Beachbuilder required approximately

11 min to clear the channel from one toeline to the other. This transit time would

be reduced the closer the dredge was working to the channel CL (less distance to

travel), and/or if only one deep-draft vessel was passing because the dredge

would not have to cross the entire channel to let the vessel pass. Total downtime

for vessel traffic may be minimized if discharge areas are available on both sides

of the channel. In the vicinity of Pass A Loutre, a discharge pipeline on the LDB

side may not be an option due to its use as a hopper dredge disposal site and the

potential hazard of a vessel grounding.

Chapter 6

Feasibility Analyses