Cutter suction dredger d’ARTAGNAN

According to The Motor Ship November 2005

The technically advanced self-propeller and ocean-going mega cutter suction dredger d’ARTAGNAN was delivered in October 2005 to the French dredging contractor SDI. The dredger is able to dredge in very hard rocky soils up to a depth of 35 metres thanks to the third generation cutting equipment developed and supplied by the Dutch company of Vosta LMG. A large cutter ladder angle is applied to obtain maximum dredging depth. A large ground reaction force is achieved through the high cutter ladder weight (in excess of 1300 tonnes). The flexibility of the new dredger is considerable and she is capable of discharging at a distance of between few metres (barge loading) to ten kilometres through a 1000mm discharge pipe. To achieve this flexibility, the newbuilding incorporates three dredging pumps: two inboard ones plus a submerged pump in the cutter ladder.

The two main pumps have variable-speed Wärtsilä 12V32 prime movers (2x6000kW or 2x5400kW), and this manufacturer has also supplied the two constant-speed propulsion and alternator-drive engines of 12V32 type, and the twin propeller installation. Each Wärtsilä- Lips CP propeller absorbs 3700kW for a sailing speed of 12.5 knots. A retractable azimuthing thruster is fitted forward to assist manoeuvrability.

D’ARTAGNAN uses completely different cutter and suction mouth types. Maximum drive torque and a relatively small cutter diameter are the basis for high cutting forces. The cutter torque, generated by two electrical motors, is passed through a sturdy gearbox. The cutter is driven via the cutter shaft and is screwed onto this shaft. Severe and heavily fluctuating loads act on the cutter shaft thread and, as a consequence, a special Millennium thread design has been selected.

The ship is provided with 11 cutter heads to suit different seabed conditions and materials. The T8 cutter heads, suited to hard rock, are 6- and 7-bladed and so far the strongest cutting system for dredgers ever built. The T8 cutter head has almost the double strength of the strongest cutter heads of the early 90s and is rated as 8,000hp.

In swell, the pontoon can generate considerable forces on the spud, via the spud carriage. These forces decrease when the link between pontoon and spud is flexible. On d’ARTAGNAN, a totally buffered spud carriage has been fitted, which is a new and revolutionary concept based on an exclusive design from VOSTA LMG. A parallel rope guide, which is hydraulicallytensioned, reduces load peaks ensuring that the dredging process is largely independent of the seaway.

Due to the fact that d’ARTAGNAN is designed to work in hard rock, normal dredging anchors are not suitable. Therefore, the two anchor platforms of approximately 250 tonnes each are provided.

Length, oa: 123.80m, Length, bp: 104.40m, Breadth, mld: 25.20m, Depth, mld: 8.20m, Draught design/maximum: 5.50/6.15m, Total power installed: 28,200kW, Propulsion engines: 2 x 6000kW, Dredge pumps: 2 x 6000kW, 1 x 3400kW, Service speed: 12.50 knots.


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