Customised cutter suction dredgers: tailored for the job, without delay

The Damen Cutter Suction Dredger (CSD) range is well known for its immediate availability. Less well known is that a wide range of optional equipment is also available from stock. This means the dredger can be customised quickly, so it arrives ready for its first dredge operation with the right set-up for the job. Olivier Marcus, Product Director Dredging, takes us on a tour of the Damen Dredging yard.

Dredging process practicalities

A stationary CSD swings from side to side, anchored on a single spud pole. After each full swing, however, the dredger needs to move forward to start the next sweep. For this ‘step’, a second spud pole is used; the dredger progresses by alternating between the two. “That’s the basic movement principle of any stationary dredger,” Olivier says. “It is fit for purpose, it works well, but you can make the dredging process more efficient and more accurate by adding a spud carriage pontoon. Instead of stepping with the spuds – which takes time – the pontoon uses a hydraulic cylinder to push the CSD forward in small increments, typically about 0.5 metres at a time. That improves dredging accuracy, reduces spill, and speeds up the work. There is another practical effect people sometimes overlook: adding the pontoon increases the vessel’s overall length, which allows for a wider swing.” 

Because the CSDs are prepared for these options, retrofitting is also possible. For example, Damen delivered a spud carriage pontoon to a CSD350 in Australia five years after the dredger itself was supplied.

Well prepared by built-in provisions

Another option the CSDs are prepared for is anchor booms. These booms lift and deploy anchors connected to side wires. Ideally, the anchors are repositioned with a workboat such as a Multi Cat. In shallow waters, however, that is not always possible – or the workboat may be needed elsewhere on the project. In those situations, anchor booms allow the dredger to keep progressing.

Due to their weight and size, anchor booms and their winches require sturdy foundations. These have already been integrated into the deck of the forward side pontoons. A similar provision has been made for a deck crane, which can be added when requested. Where these components are available from stock, they can be supplied with the CSD within weeks of the order. Alternatively, they can be shipped later if a new dredging project calls for an upgrade.

From shallow start to deep completion

Olivier points to the cutter head of a CSD. “Dredging is demanding work, and there are a few practical details you need to account for,” he says. “A dredger is brought in because a river or canal has become too shallow. At the start of the job, the cutter head needs to work efficiently in very shallow water. As the project progresses, the area is dredged deeper, so you gradually move from a shallow water situation to a deepwater one. The cutter head performs best at a specific attack angle. To keep that optimal angle at the start of the project, we can supply a wedge piece that provides the right working geometry in shallow conditions. Because it’s flange-mounted, you can remove it once you start dredging deeper. You can even add a pipe extension in the ladder, after the standard dredging depth has been reached. Versatility is key.”

Other options available as standard include different cutter teeth, or even complete soil-adapted cutter units. As soil conditions can range from soft mud to very compact sand, both the cutter’s geometry and the cutting tools can be selected to suit the material.

Knowing what you are doing – dredging instrumentation

For the dredge master, the challenge is managing a process that cannot be seen. The cutting action takes place metres below the waterline, and the dredge pump transports the dredged soil through a long pipeline to a distant spoil area. Without instrumentation, it is difficult to judge production and progress. Olivier explains: “You can’t see through the dredge pipeline, but the right instrumentation gives you a clear picture of what’s happening. To optimise production, it helps to add density and velocity meters to the dredge piping. They measure the concentration and the speed of the mixture. Put together, these data tell the dredge master what the production rate is, and where adjustments can be made for process optimisation. On longer pipelines in particular, keeping an eye on mixture velocity matters – if you pump too slowly, sand can settle in the pipe. A blocked discharge line full of sand is the last thing any operator wants.” Dredge production instrumentation and positioning systems can be easily added to a standard CSD.

Before the yard tour ends, Olivier points to a dredger that is ready to leave the yard. “This is another practical addition: an accommodation unit,” he says. “On more isolated dredge projects, it’s important for the crew to have a sheltered place to sit and eat. These standard on-stock units can be installed beneath the standard operating cabin. Many of the options we offer work like that – straightforward to integrate. Plug and play and off they go”. Another example of a short delivery time based on readily available dredgers and their smart customisation additions.