REIMERSWAAL: HIGH-SPECCED TRAILING SUCTION HOPPER DREDGER WITH SELF-UNLOADING INSTALLATION BY KOOIMAN

Reimerswaal Dredging has been active in the sand and gravel mining industry for 45 years. Since 1995, the company has been using ships with a dry unloading system, which has considerably sped up the turnaround and increased the profitability. When in 2008, the company’s two dredgers, named Reimerswaal 3 and Orisant, were sold, it provided the funds for an entirely new dredger to be built, exactly to the specifications of an experienced owner-operator.

Shipyard Kooiman was no stranger to Reimerswaal Dredging, as the company had frequently visited the yard in the past for maintenance work and conversions. Although the 6,000 m3 trailing suction hopper dredger (TSHD) they had in mind would be the largest shipbuilding project to date for the yard, the owner had no doubt Shipyard Kooiman would be up to the job. Jos Blom, director business development from Kooiman: “Our design team and the owner spent a year together designing and budgeting for the new ship, drawing on the 45 years of experience Reimerswaal Dredging has in this industry.”

Owner-captains

On 15 July 2010, the contract was signed for the construction of Reimerswaal. The principal objectives in the design were for efficient sand and gravel dredging, combined with versatility, so the dredger could be used for land reclamation or maintenance dredging if the market would require so. The result is a ship which has all the features of a typical TSHD and more. Reimerswaal Dredging is a family company with both father and son at the helm as ownercaptains. The fact that the owner will also be the daily user of the ship is visible in many crewfriendly and maintenance-reducing options. For example, there are a double number of crew cabins. When crew is changed every two weeks, there is no need to clear out the cabins. Each crew member will have his individual personalised cabin.

Builder
Shipyard Kooiman, Zwijndrecht, the Netherlands

Owner
Reimerswaal Dredging, Goes, the Netherlands

Principal particulars
Length o.a. 130.25 m
Length b.p.p. 119.75 m
Breadth (mld.) 22.00 m
Depth at 0.5 L 9.80 m
Draught Int. 7.10 m
Draught dredge 7.95 m
Installed propulsion power 5,440 kW
Speed 14 knots
Accommodation 13 people

Dredging
Max. dredging depth 60 m
Suction pipe diameter 900 mm
Dredge pump 1,800 kW
Hopper capacity 6,000 m3
Dry unloading system 2,500 m3/h

Maintenance-friendly

In order to reduce maintenance work, an automatic greasing system is installed from U.S.A.-based Lincoln. Consisting of several small grease tanks and pumps throughout the ship, shots of grease are injected via stainless tubes to various types of equipment. Another measure to reduce maintenance is visible in the exterior ceilings: a flat steel plate covers the overheads, making them a closed void space. The flat plates are a lot easier to paint than the multitude of deck stiffeners behind them.

Engine rooms 

Because sand and gravel often have to be dredged from considerable depths, the Reimerswaal is equipped with a long dredge pipe with an 1,800 kW electrically powered submersible pump on the dredge pipe. At the maximum dredging depth of 60 metres, the suction height would be too big for an inboard centrifugal dredge pump. The submersible electrical pump is driven by an ABC diesel generator set rate at 2,650 kW, which is located in the forward engine room. The same diesel engine drives a dredge pump for wet discharging to shore. Two Mitsubishi gensets, rated at 1,428 kVA, have a PTO to drive the jet pumps, which provide jet water to stir the bottom at the draghead and to liquidify the cargo for wet discharging. A third identical genset is used exclusively for electrical power. The bowthruster is a Veth-Jet thruster with two side channels. It is driven by a 1,360 kW diesel engine. While the forward engine room is dedicated to all dredge-related activities as well as housing an auxiliary generator (475 kW), the aft engine room houses the typical ship machinery, such as he propulsion engines (two MAN of 2,720 kW), the second auxiliary generator (475 kW) and all the auxiliary equipment. For economic operation, Reimerswaal’s main engines will run on heavy fuel. The tank heating system is a thermal oil system, which is pre-heated in the main engine exhausts and then heated as much as needed in a diesel fired boiler, supplied by Heatmaster.

In short, instead of the complexity of a dieselelectric installation, the owners have opted for a mainly diesel-direct driven approach, which results in a very large number of diesel engines onboard (ten, including the emergency generator), but which are easily maintainable, and have a high degree of redundancy.

The fact that the owner will also
be the daily user of the ship is
visible in many crew-friendly and
maintenance-reducing options

DP

Although she does not have a DP class notation, Reimerswaal is equipped with a dynamic positioning system, allowing her to dredge extremely accurately when combining the DP system with a track pilot. For precise speed control, the propellers are of the controllable pitch type from Schottel, with two independent spade rudders behind. The steering gear allows for exceptionally large rudder angles up to 65 degrees in either direction.

Dredging

The dredge production comes onboard through the dredge pipe, and then passes through a sieve, which discharges granulate of undesired dimensions overboard. The desired granulate is deposited into a launder, which basically is a discharge pipe above the hopper with various ports which can be opened hydraulically. The excess water on top is discharged through hatches in the hopper coaming, above the deck. These openings can be closed hydraulically when the hopper has to be filled all the way up to the rim of the coaming. On the return voyage from the mining concession, water is also extracted from the hopper through perforated pipes – located under a grille at the bottom of the hopper – which are covered with jute fibre. This makes the sand in the hopper drier, and therefore easier and quicker to discharge with the unloading system. On the outbound journey, back-flushing takes the sand out of the jute fibres again.

Unloading

The bucket wheel unloader, supplied by PLM Cranes (Heijningen, the Netherlands), is an essential component in the efficient operation of the Reimerswaal, as it allows to unload the entire hopper to shore in only two hours, ensuring short port stays.

The entire hopper is free of obstructions and shaped to accommodate the ten-metre wide bucketwheel, which is moved fore-aft on a trolley over rails and then lowered a bit after each fore-aft pass. The bucketwheel discharges onto a conveyor system, which consists of several conveyor belts, the last of which is mounted on a 46 metre long crane.

This allows discharging either over the side or over the bow, to the shore reception facilities. The advantage of a bucketwheel over a grab loader is that this process produces a continuous flow without peaks and lows and requires less input from the crew. The combination of a dynamic positioning system and the self-unloading system makes Reimerswaal also extremely suitable for precision rock fill discharging, for example to place ballast on windmill foundations.

Hydraulic Drives

The owners went to great lengths to select the appropriate hydraulic drives for the unloading system, even visiting the Thyssen Krupp yard in Rotterdam to see the bucketwheels and conveyor belts in operation. In the end, the choice for the 400 kW bucketwheel actuation fell upon Hägglunds’ Marathon MB 3200 direct drives, with good lifetime, reliability, shock load resistance and excellent torque limitation, also at blocking. The six conveyor belts are also powered by direct drives from Hägglunds. The large hydraulic power consumption was also one of the driving parameters in the electrical installation from eL-Tec Elektrotechnologie, that took care of the normal shipboard electrical installation, the ship controls and the powering and control of the dredging and self-unloading installation. To reduce the amount of hydraulic piping, the hydraulic power is generated in decentralised electro-hydraulic powerpacks, located near the consumers.

The degree of automation is exceptional according to Remko Leinenga from eL-Tec Elektrotechnologie: “The entire ship can be controlled from the helm seat. As sole electrical partner, we were able to integrate all functions seamlessly into one delivery, ensuring time savings for the yard.”

Spudpoles

With the process of dredging and unloading already as efficient as can be, the time wasted in mooring operations became a significant factor. That is why Reimerswaal Dredging B.V. specified two spudpoles in the design. These are hollow telescopic spudpoles (to allow troublefree operations above the main deck), which can be lowered by gravity and hoisted with a steel cable and winch. Besides extremely simple and swift mooring operations, the spudpoles also allow for mooring at a certain distance from the quay, which can be advantageous to line up the shore conveyor with a reception box. Furthermore, adjustments of the mooring lines because of the changing tides are not needed with spud-pole mooring.

Versatility

While typical TSHDs used for maintenance dredging are designed for a cargo density of 1.65 t/m3 in the hopper, Reimerswaal is designed for 2.2 t/m3. This means larger void spaces on port and starboard of the hopper to ensure sufficient buoyancy. The dredger is certified for unrestricted service worldwide, and her larger dredging depth means that she can be employed in areas where many other TSHDs may not. To take full advantage of this commercial advantage, Reimerswaal is equipped with all the usual TSHD attributes, such as bottom discharge doors, a rainbowing nozzle, a bow coupling for discharge through a floating pipeline, a side connection for discharging over the side and jet pumps to liquidify the cargo. In addition to multiple fixed jet nozzles in the hopper bottom, there are two large remotecontrolled jet water monitors, which can be operated from the bridge.

Wheelhouse

Although the extensive automation enables oneman-on-bridge operation, the wheelhouse itself is a vast space. Centrally, a sliding helm seat can move fore-aft between two straight consoles. All the controls which are regularly needed, both for navigation and dredging, are integrated in the armrests of the helm seat, including two screens which can display a variety of inputs. The visibility through the large windows is exceptionally good. On the bridge wings, the windows can be opened towards the inside and fixed to the ceiling, allowing the helmsman to lean outboard for a better view when mooring, or to let in a breath of fresh air. Centrally in the wheelhouse is a dinette, which can easily be used for family dinners, as a food lift leads from the galley straight to the wheelhouse.

Bruno Bouckaert