Safety & Occupational Health Office

Dredges

General Dredging

Each year, the U.S. Army Corps of Engineers' hopper dredges and bypasser dredge, work on Gulf Coast ports from Louisiana to Brownsville, Texas. Other contract dredging work is done by hydraulic pipeline dredges, hopper dredges and mechanical clamshell dredges.

Hopper dredge - propelled floating plant which is capable of dredging material, storing it onboard, transporting it to the disposal area, and dumping it.

Clamshell dredge - mechanical cable excavator dredge that uses a single bucket attached to the dredge crane with cables. The dredge operates by lifting the bucket (the clamshell), dropping it into the bottom sediments, lifting the bucket and dredged material to the surface, and emptying the dredged material into a nearby disposal facility or scows or barges for transportation to a disposal facility.

Pipeline dredge - dredge whose prime function is to excavate and move material hydraulically to another location without rehandling. The dredge is generally comprised of a ladder, cutter, suction pipe, cutter motor, hull, lever room, main pump & engine, spuds and discharge line. A pipeline dredge having a discharge diameter of 24 inches or more is called a large dredge. A class of smaller pipeline dredges that are designed to be easily disassembled for overland transporting to the next dredge site are called portable dredges. Portable dredge hulls are built in section that can be bolted together. Usually sections consist of a center hull for machinery, pump, an other equipment, and two more pontoon side sections.

Safety Tips Around Dredges

Dredges monitor marine VHF radio channels. You may contact a dredge on channels 13 or 16. It's important to know and understand the following whistle blasts from the dredge:

One blast: Pass on the left (port) side
Two blasts: Pass on the right (starboard) side
Three blasts: Dredge is backing up
Five blasts: Danger! Watch out!

Keep a reasonable distance away from the hopper dredge when it is operating. There are six hazards you may confront if you travel too closely or in the working area. They are:

1. Propellers at the back of the dredge generate strong water currents that can capsize a smaller vessel.
2. Propellers at each side of the boat at the front also can generate strong water currents that can capsize smaller vessels.
3. Large volumes of water may overflow from the hoppers underwater at the center of the dredge.
4. Powerful streams of water are automatically released from the holes at either side of the front of the dredge. These streams are powerful enough to capsize a boat or push a person under water.
5. Dredged material relocation sites may be shallower than ocean or river charts may indicate.
6. Coastal or off-shore relocation sites, which are marked on coastal charts, may have rough sea conditions due to shallower water.

Each year, the U.S. Army corps of Engineers' hopper dredges work on Gulf Coast ports from the Sabine-Neches Waterway, Louisiana, to Brownsville, Texas. Other contract dredging work is done by hydraulic pipeline dredges, hopper dredges and mechanical clamshell dredges.

Pipeline dredges have long pipelines that extend from the dredge to the shore, with underwater cutter heads sweeping back and forth across the channel. Both the dredge and pipelines are held in place with spuds and anchor lines. The anchor lines are marked for safety with yellow anchor buoys. When passing the pipeline dredges, remain on the clear side and watch for the anchor buoys. When going downstream or with the current, do not approach the pipeline. If your motor stops, the current will pull your vessel under the pipeline.

Hopper dredges move like a ship. When dredging, they move very slowly. Normally, you can tell when they are dredging by the signals on the main mast. During the day, a black ball over a black diamond over another black ball will be shown. At night, a red light over a white light over another red light means the dredge is working. These signals also indicate that the dredge is restricted in its ability to maneuver and you must stay clear of the vessel. When the dredge's hopper is loaded, the dredge maneuvers both in and out of the channel to reach the relocation site. During this time, the dredge may move much faster and may turn frequently.