No 8 MbH December 2012 voor website.jpg 58 1At its shipyard in Sliedrecht on 16th of May 2012 IHC Merwede launched the stationary cutter suction dredger (CSD) Miondo, another custom-built IHC Beaver®. The launch and naming ceremony was performed by Erica Currie, the wife of Douglas Currie, managing director of Marina & Ports Services Ltd, the future owner of the vessel. The contract for the design, construction and delivery of the CSD, was awarded to IHC Beaver Dredgers, part of IHC Merwede, by Marina & Ports Services Ltd in March 2011. The keel was laid on 6 October 2011 and the ship was handed over in the third quarter of 2012.

IHC Merwede built this innovative compact CSD for Marina & Ports Services Ltd, which is based in England. Like most of their clients, IHC Merwede has a long-term relationship with Marina & Ports Services based on mutual trust and respect as this was not the first vessel they have delivered to them. The strength of this relationship is perhaps highlighted by the fact that IHC Merwede is allowed to perform very autonomously and project management supervision from the client was reduced to a minimum.

The builder – IHC Merwede

As stated above, IHC Beaver Dredgers BV is the IHC Merwede subsidiary responsible for the delivery of this custom-built stationary CSD. What makes this CSD special and different from others is that it is a rock cutter with relatively limited main dimensions, which makes it ‘robust, though compact’. On board many IHC Merwede innovations were used, amongst which are the Cutter Special Pumps. This is not the first vessel they have been used on, but on this occasion the restricted space available for them made a custom solution necessary to find the optimal location.

Miondo’s dredging characteristics

The Miondo is a custom-built IHC Beaver with a capacity of 4.836 kW. The stationary CSD is designed for dredging a wide range of materials and is capable of cutting rock at a maximum dredging depth of 17 metres. With a length of 63 metres the vessel is very compact and every available bit of space has been used to pack in all the necessary technology and equipment.

The vessel is equipped with one submerged single-walled and one inboard fitted doublewalled Cutter Special® Pump, both of which are specially designed with a large sphere passage for cutter suction dredging operations. The vessel’s submerged dredge pump is driven by a frequency-controlled electric motor via a flexible coupling and a special gearbox designed for underwater operation. The inboard dredge/ booster pump is driven by a dedicated diesel engine through a clutch coupling, gearbox and flexible coupling. The inside diameter of the suction tube is 650 millimetres. The cutter driveline is driven by a frequency-controlled electric motor. The output shaft is rigidly connected to the cutter shaft on which the cutter crown is mounted. The dredged slurry is pumped ashore to the desired location through a floating discharge pipe.

No 8 MbH December 2012 voor website.jpg 58 2The vessel is not self-propelled and consequently does not have main engines for propulsion, whilst the electric requirements are supplied by the generator sets. However the onboard anchor boom for handling the swing anchors and spud-tilting installation allows it to operate in remote areas with limited support equipment.

Accommodation and equipment

The superstructure accommodation of the Miondo is suitable for four crewmembers in ‘day-use’, no berths or cabins are provided for overnight stay. Only limited crew is required for the operation of the vessel and its equipment, dredging control for example, can be executed by only one person. A subsidiary, IHC Systems, is responsible for the development, manufacture  and supply of instrumentation, control, and automation systems. This guarantees the implementation of in-depth knowledge of the field of industrial instrumentation and control technology.

No 8 MbH December 2012 voor website.jpg 58 3As mentioned above, the CSD is ‘robust, though compact’, meaning all the used equipment is ‘heavier and stronger’ than one would expect on a CSD of this size. Spud and swing anchor installation, cutter ladder, winches are all relatively ‘oversized and overweight’ in comparison to the vessel appearance at first glance.

Dredge pump technology

With the Miondo being the first vessel of this size in which the IHC Parts & Services developed Cutter Special® Pump is used, it is appropriate that these pumps and their design are investigated more closely. Cutter Special® Pumps are either single- or doublewalled, subject to whether they are inboard or submerged. They are available in various pressure categories up to 40 bar, with suction diameters from 250 to 1,400 millimetres. Inboard dredge pumps are the primary power source for transporting the mixture to a hopper, barge or discharge location and are essential for mixture transport in stationary dredgers, like the Miondo. Submerged dredge pumps are located in the suction pipe on the cutter ladder and transport the mixture from dredging depth to the surface.

No 8 MbH December 2012 voor website.jpg 58 4Single-walled pumps have a simple compact design and are easy to maintain. Double-walled pumps are fitted with an additional external pump housing allowing the internal pump housing to be constructed out of extremely
No 8 MbH December 2012 voor website.jpg 58 5

Striving for a high level of innovation,
with care for the environment

wear-resistant material. This also means a smaller part of the wall thickness is needed for mechanical strength and a larger part is available for wear losses. The outer housing also offers better protection: in case of damage to the internal pump housing, the outer housing prevents flooding of the pump room.

58 11111The Cutter Special® Pump has been developed specifically for use on cutter suction dredgers. The enlarged width of passage of the pump allows the dredger to pump rocks and bigger stones without any difficulty. The relatively large diameter of the impeller results in a higher efficiency and high suction capacity. Whilst the accessibility needed for maintenance work is as good as with other (more conventional) pumps. When dredging rocks, the special characteristics of the pump result in an increase in the number of working hours and increased production levels.

Other essential elements in pump design for dredging are the seals around the pump shaft and the use of wear-resistant materials. The problem here lies in the material to be dredged: this is almost always abrasive, sometimes to extremes when you consider rocks. Looking at it from a logistical and economical point of view: the threat of wear does not so much lie in the direct cost of an item to be replaced, but in the resulting downtime due to installation and/ or replacement time. An installation which is not working while undergoing maintenance or repair can cost many times more than a worn part.

Innovation and environmental care

IHC Merwede focuses on the continuous development of design and construction for a number of specialist maritime sectors, like dredging vessels and equipment. They have in-house expertise for engineering and manufacturing innovative vessels and advanced equipment, as well as providing life-cycle support. Technological innovations are the company’s underlying strength through its continuous investment in research and development. Moreover, it helps to safeguard a sustainable environment.

Tom Oomkens