Dredge Maneuvering Characteristics

Dredge Maneuvering Characteristics

The dredge maneuvering characteristics were determined by calculating the

respective characteristic components from data reduced from several sources,

including: the contractor's daily dredge report and daily submittals on Engineer

Form 4267 "Report of Operations Pipeline, Dipper, or Bucket Dredges,"

supplemental notes taken by USACE and contractor personnel, and from the

time-series data of the dredge or dustpan x-, y-, z-position and slurry density and

velocity. Some minor time discrepancies were noted between these different data

sources. These discrepancies are due primarily to different personnel manually

logging the entries at different times.

Relocating the hard point

The time interval for moving the hard point from Reach 1 to Reach 2 that

consisted of adding 3,600 ft of submerged line was 43 hr 45 min (time from

dredge shutdown at 1645 on 6 June to startup at 1230 on 8 June). To determine a

"typical" time interval that could be used for future project planning and esti-

mating, this interval should be adjusted by evaluating the effects of two factors:

work was suspended during the hours of darkness due to crew safety concerns of

this first-time demonstration, and the move was made before it was scheduled

because of the request to relocate the dredge due to the rapidly developing shoal

(described in Chapter 2). Once experience is gained on operating at night and a

safety hazard risk analysis is performed, the night-time operating restriction may

be lifted. The amount of time that work was delayed (due to darkness) on moving

the hard point consisted of 5 hr 18 min on 6 June, 10 hr on 7 June, and 5 hr

45 min on 8 June, for a total of 21 hr 3 min. The subtraction of the night-time

hours from the total interval results in 22 hr 42 min to float the submerged line

(fill with air), disassemble, add sections, and move the hard point. This time

could have been further reduced if the contractor had planned for the move by

having the additional pipe connected and standing by. The contractor estimated

that had the move been planned with the additional submerged pipe and handling

equipment standing by, the total time to move the fixed point would have taken

approximately 12 hr.

Anchor handling

The anchors were handled for three basic reasons during the demonstration:

to initially set them in Reach 1, to reposition anchors that were dragged during

the tension-setting tests and during dredging, and to reposition the anchors in

Reach 2. There was one instance where the cross-channel anchor outside the

LDB channel toe was impeding a hopper dredge placing material into the

disposal site in Pass A Loutre, and the anchor was promptly repositioned. The

anchor-handling times depended on the availability of the tugs, where the

anchors were being moved from and to, vessel traffic impacting the cross-

channel anchor handling, and (where precise anchor positioning was required,

i.e., ensuring the anchor was placed outside the channel) availability of the

survey vessel. Seven anchor-handling events were logged. Durations ranged from

Chapter 4

Dredging Operational Characteristics Analyses