Boskalis' new deep suction dredger 'Hollandsch Diep'

In November 2002 the new deep suction dredger 'Hollandsch Diep' was delivered by De Groot Nijkerk Dredging Equipment to its owner Royal Boskalis Westminster NV.
Since then the dredger has been stationed in the 'Zevenhuizer Plas', a lake near Rotterdam in the Netherlands where sand is dredged for several large infrastructural projects.
Together with this dredger De Groot Nijkerk also delivered three booster stations.
In combination with these booster stations the 'Hollandsch Diep' is able to pump sand over a maximum distance of approx. 13 km which means that costly and inconvenient transportation by road can be avoided.

De Groot Nijkerk which is specialised in customized dredgers and dredging systems already delivered two other deep suction dredgers to Boskalis some twenty years ago: the 'Rosalien' and the 'Marcolien'. The experience of these two dredgers, which both still perform very well, was used for the design of the 'Hollandsch Diep'.
But Boskalis wanted the 'Hollandsch Diep' to be more powerful and able to dredge deeper.
This resulted in a custom-built dredger that has been built according to very specific requirements of Boskalis:
-Flexibility to be deployed fast anywhere in the Netherlands
-A large dredging depth (60 m)
-The possibility to pump sand over a wide range of distances without power loss

Dismountable

To be able to deploy the dredger at any sand win location in the Netherlands it has been built in such a way that it is completely dismountable and can be transported by road in which case 12 trucks are needed to carry all the components.
In total the dredger is built up from 7 pontoons:
-One central pontoon of 14.5 x 3.3 x 2.8 m carrying an inboard diesel driven dredge pump.
-Two rear side pontoons of 18.0 x 2.75 x 2.25 m.
-Two front side pontoons of 15.5 x 2.75 x 2.25 m.
-Two separate pontoons of 8.0 x 2.5 x 2.25 m in front of the dredger carrying a supplementary gantry for hoisting the suction pipe; these pontoons are connected to the dredger with two steel pipes.

Dismounting the dredger and putting it back together elsewhere until it's fully operational takes less than a week, which is relatively fast for a dredger of this size.
To make this possible special attention is given not only to the joints of the steel components but also to all the electrical wiring. That is why at every connection of the pontoons easy to use electrical plugs and sockets are installed.

Dredging depth

With the increasing demand for sand and the limited possibilities to start new win locations in the Netherlands, it is necessary to dredge sand at ever-greater depths.
To be able to maximize the production of existing sand win locations, the 'Hollandsch Diep' is designed with a maximum dredging depth of 60 m.
To achieve this it is equipped with an electrically driven underwater dredge pump that is mounted on the ladder of the suction pipe on a depth of 18 m.
The power for this underwater pump (600 kW) is delivered by a powerful Caterpillar 3508 B diesel engine that is installed in one of the side pontoons of the dredger.

A diesel engine with constant power

Boskalis required that the new dredger could deliver an optimal sand production rate at every possible pump distance until the maximum of 13 km.
Therefore it had to be possible that the inboard dredge pump could work at a large range of different speeds.
Possible solutions would be the installation of a continuously variable gearbox or a frequency controlled electrically driven pump, both very costly solutions.
On the 'Hollandsch Diep' another completely new technology is used. This technology involves an electronically modified standard diesel engine, in this case a 1,120 kW Caterpillar type 3512 B diesel engine.
This engine has the advantage that already in its standard configuration it has a relatively large range in which it can deliver a constant power, either between 1,400 and 1,800 rpm or between 1200 and 1600 rpm.
By changing the electronic control of this engine Caterpillar has succeeded in extending this range so that it can now deliver a constant maximum power over an exceptional wide speed range between 1,200 and 1,800 rpm.
A range that perfectly suits the requirements of Boskalis.
The resulting engine is indicated as a Caterpillar type 3512 B WOSRE, which stands for “Wide Operating Speed range Engine”.
Besides in the 'Hollandsch Diep' itself this type of engine is also installed in the three new booster stations. The configuration of all these engines is the same, which means that they are completely interchangeable.
The engines of the booster stations can be remotely controlled from the bridge of the 'Hollandsch Diep' by means of a wireless remote control communication system.

Finally

With the 'Hollandsch Diep' and the three booster stations Boskalis disposes of a very modern and advanced sand dredging equipment with a high degree of cost efficiency.
The 'Hollandsch Diep' will certainly play an important role in the supply of sand for a great number of projects in the oncoming years.

Main characteristics

Total installed power 2,350 kW
Power underwater pump 600 kW
Power inboard pump 1,120 kW
Length o.a. 82.0 m
Length over pontoons 61.0 m
Width 8.9 m
Draught, 50% bunkered 1.1 m
Suction pipe 550 mm
Discharge pipe 500 mm
Dredging depth 60.0 m

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