International

Hopper dredge solutions

A Hopper dredger excavates materials from the seabed, primarily by forward movements and suction power, through an extendable suction pipe and a draghead. The on board hydraulic installations of these hopper dredgers are usually very exhaustive. Largely because a lot of specific movements (each with their own requirements) have to be carried out. To tackle these movements, we have developed product packages.

Bottom door system

A hopper dredge bottom discharge system is primarily used to release its contents through the hopper's hull. Discharging the dredger's sediments happens through opening up its hull doors, ensuring fast and effective unloading of the hopper dredge. The hull doors are operated by rods that are actuated by large hydraulic cylinders, generally mounted above the cargo hold.

Pre-dumping door system

When a hopper dredge discharges its materials in very shallow water, its hull doors cannot be used. In this case pre-dumping doors are the perfect alternative. The pre-dumping doors are operated by means of large hydraulic cylinders which, in turn, are controlled by special 4/3 way-valves.

Self-suction channel door system

Self-suction channel doors are installed above the hull doors, forming the topside of the suction channel. The system is controlled by a large hydraulic cylinder, located above the hopper's cargo load.

Overflow system

Within a hopper dredge water is automatically separated, by physical laws, from the sediment. When the sludge enters the hopper dredge, the sediment starts sinking to the bottom while the water remains on top. The unneeded amount of water is removed by an overflow system that is controlled through a hydraulic winch system. In this way the retention of solid materials is maximised and therefore results in more efficient hopper dredge processes.

Gantries

Typical gantry solutions that are installed aboard hopper dredgers are A-frame gantries (draghead, pump and intermediate), both parallel and wagon type (trunnion gantries). All in order to support the hopper suction pipe handling processes. Gantries installed on a hopper dredge have a hoisting capacity of 30 up to 630 tons. These gantries are normally equipped with one or two large hydraulic cylinders, which are protected by means of flow-control valves and controlled by means of (proportional) 4/3 way-valves, located below deck.

Heave compensation systems for dredgers

Passive heave compensation

The dredging process is made far more effective when the draghead is equipped with a heave compensation system. A heave compensator ensures that the draghead continues to work with the right distance between draghead and the bottom floor. Next to that, it ensures the right pressure on the seabed despite unavoidable roll, pitch and heave movement of the dredge. Rope strainers improve workability and control by ensuring that the cables are always tensioned. These compensators consist of single acting large hydraulic cylinders, a series of air/oil pressure valves and a locking valve block. These enable the operator to lift the draghead without compressing the cylinders, and provides a safety function in case the steel wire rope breaks.

Active heave compensation

Next to the more traditional (passive) heave compensation systems described above, Bosch Rexroth offers active heave compensation systems. In addition to the functions described in the previous paragraph this active heave compensation system will position the draghead accurately on the seabed. It requires only an extra hydraulic power unit and accumulator, using relatively little additional deck space.

Bow coupling and rainbow equipment

Efficient dredge results are unlikely without the ideal bow coupling and/or rainbow system. One effective means of raising dredger productivity and functionality is by installing a bow coupling. This bow coupling system often consists of a hydraulically driven winch and several hydraulic locking cylinders. For rainbow and bow coupling functions, sluice valves with hydraulic cylinders are also required.

Active draghead system

The draghead of a trailing suction hopper dredger represents the first mechanical contact with bottom material. So its design, quality and sturdiness are critical in dredging and sedimentary mining tasks. Dragheads are frequently equipped with hydraulics for visor adjustment and water admission to optimise the dredging process. Together with various draghead designers, Bosch Rexroth has engineered optimal solutions for these active dragheads.

Hydraulic buffers for suction pipes

Hydraulic buffers are available to help ensure that the suction pipe is brought safely into the correct position on board, without bumping up the hull. The result is that the suction pipe and hull remain intact without any damages.