IHC Merwede’s TSHD Specifically Designed for the People’s Republic of China

Recently the naming and launch ceremony for Chang Jiang Kou 02 was celebrated in Qidong, China, whilst at the same time in Kinderdijk, the Netherlands, her slightly older sister Chang Jiang Kou 01 was completed and handed-over. Chang Jiang Kou 01, the first of the two Trailing Suction Hopper Dredgers (TSHD) was built at the IHC Merwede shipyard for the Yangtze Estuary Waterway Administration Bureau MOT, which is based in the People’s Republic of China. The TSHD is named after the estuary of the Yangtze river, which is where the world’s busiest container port, Shanghai is situated, hence the need for these vessels to maintain the estuary.

The contract for the design, construction and delivery of two 12,000 m3 TSHDs was signed in July 2008. The keels for both dredgers were laid at the same time in December 2010. Whilst number one is already finished and delivered, number two is scheduled for delivery in the first quarter of 2013. This delay in building sequence was a deliberate decision. For several important reasons the choice was made to build one TSHD in the Netherlands and the other one in China.

Traditionally the Chinese government have always allowed IHC Merwede to build their ‘flagship’ first of class vessel at their facility in Kinderdijk. This can be seen as an expression of great honour and respect for (the building quality of) IHC Merwede and the Netherlands. The delayed start of the building process of the second TSHD in Qidong is to make full use of the experience gained in constructing the first vessel. The management and coordination of the second vessel is also completely in the hands of IHC Merwede’s staff, for obvious reasons. Overall, the construction of the second vessel is on schedule, demonstrating the cooperation of IHC Merwede and its partner in China, regarding international production. Most equipment and machinery on board both vessels is of European or even Dutch manufacture to guarantee the best quality.

Building for the People’s Republic of China means on the one hand the opportunity for IHC Merwede to build according to their own corporate style and identity, while, on the other hand, it meant understanding the Chinese culture and heritage.

Dredging in the estuary of the Yangtze

The traffic on the Yangtze river and in the delta is still growing rapidly in terms of overall size and throughput. This continued growth makes the dredging of a deep navigational channel an urgent priority. The Chang Jiang Kou class vessels have been specifically designed to assist in the realisation of this aim, with the high-current velocity and soil properties of the river in mind.

The Yangtze estuary is the lower, tidal part of the Yangtze and stretches some 700 kilometres. Near its mouth, it forms a delta comprising three smaller rivers and numerous streams. Here, salty sand deposition continually creates new land. The estuary carries an average of 30 million litres of water per second into the East China Sea; its average depth is seven metres, and the average tidal range at its mouth is 2.7 metres. To compensate for the high-current velocity at a relatively shallow water depth, the TSHD is fitted with two main engines, each delivering a 7,500 kW. At first sight this kind of power may appear to be ‘over-the-top’, but it is an absolute must to maintain a speed of four knots against the current with a barge along side.

The sediment movement in Yangtze Estuary is very complicated; there are both suspended loads and bed loads. They are influenced not only by runoff but also by tidal currents, wind waves and salinity. The extremely small grain size of bed material requires dredging equipment that can handle very compacted fine sands with a high SPT (Standard Penetration Test) value and an average of 0.075 millimetre in diameter. This is one of the reasons why the vessels are equipped with the patented IHC Merwede Wild Dragon® drag head.

Operating characteristics

The Chang Jiang Kou vessels are especially designed and equipped for operating in the environmental parameters that are typical for the Yangtze river. One of the characteristics of the design of the vessel is the capability to manoeuvre and operate in shallow waters with a high-current velocity, whilst having a barge for cargo moored alongside. Because of the density of the dredged material, the diameter of the sand particles and solubility of the dredging material in water, the soil will not settle in the hopper and/or barge. The barge can remain moored at a fixed position and there is no need for complex mooring equipment to move the barge during loading. Only Sea Guard fenders (2,500×2,500 millimetres) and relatively simple winches will suffice.

For the vessel to carry out maintenance dredging jobs over a distance of 122 kilometres in one of the busiest waterways with a very high traffic volume, there are high demands on the vessel’s manoeuvrability. For that reason this TSHD is equipped with a high speed steering installation, enabling the vessel to quickly respond to traffic situations and giving the vessel a small turning circle.

Dredging characteristics

The Chang Jiang Kou 01 is equipped with two suction tubes with a diameter of 1,000 millimetres, one on either side of the vessel. Without an additional submerged pump a dredging depth of 25 metres can be achieved. The TSHD has a central pump room, just behind the hopper, in which the two dredge pumps are installed. The dredged spoil can be dispensed into the vessel’s own hopper of 12,000 m3 capacity or into a barged moored alongside on starboard, through a single T-shaped loading branch with a forward and aft exit. When the vessel’s own hopper is full, the TSHD sails to a disposal area and either dumps the material through the ten doors in the hull bottom or pumps the material out of the hopper. When emptying the hopper with the pumps the material, mixed with water, can be transported ashore through a floating pipeline. The barges are self-propelled or can be separately transported by means of tug or push boats, when full.

In the port and starboard double bottom of the hopper, a jet supply line has been fitted so that the jet pumps, at the forward end of the hopper, can pump water to the hopper to dilute the hopper load (during shore delivery or when dumping the hopper load through the bottom doors). The vessel has an AMOB system, a provision to directly pump poor mixtures (too low density overboard instead of into the hopper. (AMOB = Dutch abbreviation for Arm Mengsel Over Boord = Poor Mixture Overboard). The overflow is a single bowl located on centreline at the forward end of the hopper and provides a way out for superfluous water. The overflow is telescopic and continuously adjusts to the filling level of the hopper. The dredging process is controlled from the wheelhouse; the suction tubes and the drag heads are handled by means of two gantries and winches powered by one suction tube winch motor and one intermediate winch motor. This configuration can be found on starboard as well as on port side.

Propulsion and auxiliary equipment

The engine room is situated in the aft part of the ship and has a funnel above. In the engine room two M.A.N. main engines are situated, each producing 7,500 kW. Both engines drive a controllable pitch propeller. Furthermore we find one auxiliary generator and an emergency generator, both Caterpillar. Two free hanging fish-tail rudders are fitted aft of the two nozzles with the propellers.

The bow area of the vessel comprises two bow thrusters each driven by an electric motor. This is also the location where, of course, the anchoring equipment is situated.

Accommodation and wheelhouse

The Chang Jiang Kou 01 can accommodate 37 crew members, a much higher number than we would expect on an average (European) TSHD. The Chinese culture requires a strict and dedicated separation of ranks and functions; according to Chinese customs, dedicated crews and officers are strictly separated. This is evident not only in the wheelhouse arrangement and the accommodation lay-out, but also in the use of separated crew and officers mess rooms. The galley equipment is also slightly adapted to the preparations of Asian food, here, for example, we find a traditional oil wok burner. Obviously the navigation bridge deck does not feature the average single man bridge: steering/navigation crew is solely dedicated to that specific task and a separate crew is present to perform all dredging tasks. The wheelhouse contains a larger than normal W-shape navigation desk allowing for enough space to accommodate an officer and several crew members, each behind their own instruments.

Below the navigation bridge deck, we find a non-full height deck, of approximately 2.2 metres, that contains all converters, computers, air-conditioning etcetera to feed all bridge instruments, connecting control panels and cool the accommodation. The complete nautical, navigation and communication package contains the common state of the art equipment, including most essential IHC Merwede in-house developed dredging instrumentation.

Deck lay-out

Besides the normal deck equipment, like bollards, capstans, winches and anchor equipment, there is a deck crane of 22.5 tons for changing/servicing the drag head, hoisting spare parts and transporting equipment.

The IHC Merwede Signature

With this class of vessel IHC Merwede proves once more they are amongst the market leaders of building dredging vessels and delivering dredging equipment. The mutual respect and association between the Chinese government and IHC Merwede has been demonstrated again as the flag ship of Yangtze fleet is built in the Netherlands and the second vessel locally in China. A further demonstration of the respect held for IHC Merwede by the Chinese government is the fact that they have been entrusted with the design and production of a class of TSHDs specifically to meet the clients requirements.

Tom Oomkens