DCI DREDGE XIX: TSHD FROM IHC MERWEDE PLAYS MAJOR ROLE IN PREPARING INDIAN PORTS FOR 21ST CENTURY

DCI Dredge XIX, a 5,500 cubic metre Trailing Suction Hopper Dredger (TSHD), is the latest addition from IHC Merwede to the Indian dredging fleet and will help India prepare and maintain the standards they are setting themselves for their port services. The TSHD has been built for the Dredging Corporation of India Ltd (DCI), based in Visakhapatnam, on the eastern seaboard of India. DCI is a semi-government organisation, founded in 1976, and is part of the Ministry of Shipping. It provides services to the major ports, maintaining the depths of shipping channels of India’s 7,500 kilometres of coastline.

On 2 April 2012 DCI Dredge XIX was launched at the IHC Merwede facility in the Dutch municipality Krimpen aan den IJssel on the south shores of the river IJssel. Launched by Sunitha Vasan, spouse of the Union Minister of Shipping, this TSHD is the latest product of the long relationship between the two parties that lists some ten vessels to date and is the first of a series of three vessels to be constructed over the next two years. The ceremony was performed in the presence of His Excellency G.K. Vasan (Union Minister of Shipping), His Excellency Pradeep Kumar Sinha (Secretary of Shipping), Her Excellency Bhaswati Muhkerjee (Ambassador of India to the Netherlands), Captain D.K. Mohanty (chairman and managing director of DCI) and other officials of the Indian Ministry of Shipping, DCI, the shipyard and classification societies.

What’s in a name . . .

The name DCI Dredge XIX might not evoke lofty thoughts and emotions; nevertheless this vessel will have an important role in securing the future of many Indian seaports. As His Excellency G.K. Vasan stated in his address during the launch ceremony: “India is striving to achieve 14 metres of draft in all her major ports and 17 metres in the hub ports.” He also applauded the continuing cooperation between IHC Merwede and the Dredging Corporation of India that had produced the vessel since the initial signing of contracts on 29 April 2010. The minister expressed the hope that the excellent bilateral relations would continue in the future. A confirmation of the above can be found in the fact that DCI Dredge XIX is to be the first of three such THSD vessels. This initial contract having been for two vessels with an optional third, however this option was exercised soon after the first build got under way.

DCI design philosophy

DCI Dredge XIX is designed to work the Hoogly River, which is a tributary of the Ganges in West Bengal, known for its shallow depth and strong high-speed currents. These conditions are some of the most extreme a dredger can operate in and special measures have been taken in the design and construction of the vessel to accommodate them. These measures include powerful engines, in this instance two 4,100 kW units, and a special hull form with a sophisticated bulbous bow, just to name a few. This vessel is also capable of stationary dredging. A dredger would usually spend much of its time going ‘slow ahead’ at a speed of about five knots. The Hoogly, however, has a flow of five knots most of the time and so a higher speed is required to ‘make way’ against it. With a top design speed of 14.1 knots this THSD is well equipped to do this. The speed is achieved by means of a controllable pitch propeller drive and the engines have the capability of providing the power for this extra load.

In addition to the modified hull shape, the vessel has a bulbous bow, which is a characteristic of designs for the owners DCI. Other typical characteristics for the DCI TSHD design philosophy are the conical bottom valves for

dumping spoil out of the bottom, the forward superstructure and the dual suction tube configuration. The two suction tubes of 700 millimetre diameter, one on either side of the vessel, allow for simultaneously dredging on port as well as on starboard side. In most other respects the vessel is an ‘IHC-standard’ TSHD, as far as one can use the word ‘standard’.

DCI Dredge XIX characteristics

From a project point of view the vessel has been built to two classification standards, Lloyd’s Register and the Indian Register of Shipping (IRS).

Indian TSHD also capable of stationary dredging

The IRS is authorised by the Indian flag state to inspect the implementation of the statutory requirements on their behalf and the only requirement once the vessel is in India. The dual classification is merely a way by which a vessel can be built in the Netherlands for the Indian sub-continent. This entailed the use of two separate surveyors, as there is currently no operational agreement between the two societies.

As stated above, it is normal for these DCI vessels to have the superstructure set at the far forward end of the vessel, with the main machinery room and the pump room aft and the hopper in the middle between the two. Under the accommodation are technical spaces with the jet pumps, the bow thruster room and the forepeak. Two dredge pipes, one to starboard and one to port, feed the directly driven main dredge pumps in the aft ship. The dredging system control is provided by IHC Systems a division of the parent company.

Wheelhouse and accommodation

The wheelhouse forward area contains the main navigation consoles with all the usual navigation and ship control facilities. This is the so-called Captain’s area and designed for sailing in the conventional sense. The aft part of the bridge is the operational area for dredging activities and is home to the ‘Dredge Master’. Here there are two identical control systems, one for each dredge pipe in a single combined console on the vessels centre line. This combined console allows the two dredge pipes to be employed simultaneously. Below the wheelhouse is a converter room housing most of the electrical junction boxes, control units and the HVAC system to support the bridge and accommodation.

The crew accommodation is to be found on the superstructure decks, between the wheelhouse and the technical spaces in the hull. The vessel has a crew of 35 people, which is normal by Indian standards, but may seem quite a lot to European standards. To accommodate the national habits, separate facilities with specific accommodation and messes for officers and crew are provided.

Dredging facilities

DCI Dredge XIX is designed to dredge to a maximum depth of 25 metres. A swell compensating system has been installed to maintain the dredge mouth position and pressure on the seabed at all times whilst the vessel is dredging on the move. To facilitate the stationery dredging capability, a stationary suction mouth can be fitted with high-pressure jets, which loosen the river bottom by injecting high-pressure water into it.

IHC Merwede and DCI assure Indian
ports are ready for 21st century

During normal trailing dredging the drag head teeth, which are no longer useful when the vessel is stationary, cut into the riverbed in the normal fashion. When stationary dredging, the system can maintain the required distance from the seabed to allow the pressure jets, referred to above, to work at their most efficient. For this purpose an additional swell compensating system has been installed.

The vessel is capable of discharging the dredged spoil by three different means. It can be dumped out of the bottom of the vessel through conical valves in the vessels hull of which there are nine to port and nine to starboard of the hopper. It can be pumped ashore through a floating pipeline or finally by rainbowing. This means discharging from the bow by means of a high-pressure spray to create an area of reclaimed land, wherever desired by the customer at the time.

When the vessel is being discharged by either of the two pumping methods, a water injection pump is employed which liquefies the spoil to allow it to be moved around. At the bow is the coupling for a floating pipe and the rainbow nozzle. To accommodate the piping ashore, the vessel was delivered to the new owners complete with 300 metres of floating discharge pipe. The hopper includes an overflow system, designed to optimise the efficiency of the dredging process by ensuring the maximum retention of solids in the hopper in parallel with fast discharge of water overboard.

The vessel is also fitted with a degassing plant, as the dredger can operate in areas where natural gases are trapped or dissolved in the dredged material. As the soil comes to the surface and is exposed to a reduced pressure, the gases within it expand and are released to atmosphere, in so doing it reduces the density of the mixture. This all happens prior to passing through the dredge pump. Clearly this can radically reduce dredging efficiency or completely stop the dredging process all together. Also, because these gases are typically organic by nature, they can be toxic and potentially explosive. All precautions are taken to prevent these dangerous situations; a degassing installation is integrated into the plant for this very purpose whilst at the same time preventing downtime.

Main propulsion system

The main propulsion package consists of two marine diesel engines, which produce 4,100 kW at 750 rpm each. The same manufacturer also supplied the gearboxes and the controllable pitch propellers in nozzles including the propulsion control and monitoring system. To enhance the manoeuvrability the vessel has two tunnels thrusters in the bow. The main engines also drive the main shaft generators.

Electrical system

One of the leading Dutch versatile providers of electrical engineering services designed and installed the electrical systems, including the vessels alarm and control system. In addition they provided the main switchboard complete with a power management system. Two 1,500 kW shaft generators, running at 1,500 rpm, 9 generate the ship’s primary power and feed the electrical systems. In addition two harbour generator sets each produce 465 kW, again at 1,500 rpm.

The wheelhouse comprises an extensive package of navigation and communication equipment. The Dredging Control System is provided by IHC Systems, a division of the parent company. The vessel also has integrated side scan sonar and all other relevant survey equipment on board. Special equipment, like a DGPS log for accurate indication of the movement of the vessel during dredging operations and radars with high-speed processors generating a smoother image rotation, was included in the package to optimise safe navigation.

Deck equipment

On the aft deck two winches with large horizontal wire drums and four (two times two) bollards are situated for mooring purposes. The rope baskets, guide rollers and the stern anchor equipment (again with a horizontal rope drum on either side) complete the aft anchoring and mooring equipment. Two heavy lift cranes are fitted: one at centreline on the aft deck and one on the portside gangway, which is capable of spanning the entire hopper. These cranes are for lifting dredging equipment and maintenance purposes, like changing the dredging mouths. An additional (smaller) crane is fitted forward of the superstructure

On port as well as on starboard side two gantry cranes (with heave compensation) are installed for the handling of the suction pipe assembly. The required lifeboats on both sides are installed in the matching davit installations. On the foredeck six (two times three) bollards, complemented with two rope baskets, four (two times two) guide rollers, two bow anchor winches (each with a horizontal rope drum) and two mooring winches are situated.

Tom Oomkens & Andrew Rudgley