Noname Article 630

The world?s largest trailing suction hopper dredger, Jan de Nul?s Vasco da Gama, built at German shipyard Thyssen Nordseewerke, and is about to start work.

With a capacity of 33,000m³; – equivalent to 58,000 dwt ? Vasco da Gama has a hopper approximately 40 per cent larger and carrying capacity approximately 70 per cent greater than its nearest rivals, Royal Boskalis Westminster?s W D Fairway and Queen of the Netherlands, each of which has a capacity of approximately 24,000m³.

Intended primarily for use on large scale land reclamation jobs, Vasco da Gama will also be used for offshore projects such as trenching, pre-sweeping, and rock dumping in deep water, but its size makes it particularly well suited to the land reclamation role.

Unlike other dredgers such as cutter suction dredgers, which pump sand over comparatively short distances using pipelines, trailing suction hopper dredgers also transport the material they remove from the seabed, thus making hopper capacity a key consideration.

Time spent transporting sand is unproductive for a dredger, and the larger the vessel the fewer trips are required, and since the first ?jumbo? trailing suction hopper dredger, the 17,000m³ Pearl River, was introduced into service, hopper capacities have grown steadily.

Several contractors now operate vessels in the 18,000-23,000m³ range, but the capacity of Vasco da Gama is such that on a single voyage it can transport 2-3 times the load of most competing vessels.

Another key feature of the latest generation of ?jumbo? trailing suction hopper dredgers exemplified by Vasco da Gama is the ability to work at great depths. As demand for clean sand for reclamation work has grown, so dredging contractors have had to work further and further offshore to obtain it.

For this reason, in addition to its very large capacity hopper, Vasco da Gama is also capable of working at depths that exceed those of any other dredger.

With the hopper empty, and its twin 1,400mm diameter suction pipes inclined at an angle of 60 degrees, Vasco da Gama is capable of dredging material at a depth of 125m, although, as currently configured, it is not yet equipped to do so. As the shipyard explains, however, it was designed and built with foundations capable of accepting larger, heavier equipment at a future date.

With a shortened suction pipe, inclined at an angle of 55 degrees it is well suited to working at depths of around 80m, but with hopper loaded it will also be capable of work as deep as 131.50m. The huge suction pipes ? with integral submerged dredge pump and draghead attached ? are raised and lowered using four massive gantries.

Vasco da Gama?s twin 1,400mm diameter suction pipes are also equipped with world`s largest submerged dredge pumps (5,500 kW), enabling the enormous hopper of to be loaded with 33,000m³; of dredged material in a record time of just one hour.