Transnet National Ports Authorities (TNPA)
Transnet Ltd. is the largest state-owned enterprise active in the logistics chain in South Africa. Every day, the company delivers thousands of tons of goods in and around the country. It administers and maintains railways, trains, logistic centres, fuel and gas pipelines, pump stations and cargo terminals in seaports. So it plays a crucial role in the economic growth of South Africa and the improvement of the quality of life throughout the country. The National Ports Authority of South Africa in Johannesburg is a division of Transnet Ltd, with a mandate to control and manage eight commercial ports located on the 2,954 kilometres of the country’s coastline: Richards Bay, Durban, East London, Port Elizabeth, Nqqura, Mossel Bay, Cape Town and Saldanha. The markets in the hinterlands of these seaports largely determine the nature and types of cargo handled at each of them. The company is a firm believer in core values such as open and honest communication, service excellence, human dignity and cultural diversity, employee participation and empowerment, integrity in business conduct and the well-being of communities in which they operate.
TNPA Dredging Services
For the successful fulfilment of its mandate to provide a world-class port system, TNPA also performs the dredging work through its business unit Dredging Services. The products and services of the highly specialised team of 160 people comprise dredging and hydrographics, survey planning, management and execution. These works require trail dredging, grab dredging, bed levelling and beach nourishment. Only large capital dredging jobs are left to third parties.
Dredging Services operates with two 2,830m3 TSHDs, one built in Germany (1977) and one at IHC Dredgers, Kinderdijk (1981). Both can dredge at depths of 30 metres with a trailing pipe and at 26 metres with a stationary bow pipe. There is also a 400m3 grab crane hopper dredger with a dredging depth capacity of 14 metres for dredging in limited areas. A plough bed leveller vessel keeps waterways level, and a fleet of four modern high-speed survey vessels allow hydrographers to produce bathymetric maps with accuracies of 10cm. The entire TNPA fleet has been equipped with hydrographic dredging processing and presentation systems.
Retrofit of TSHD INGWENYA
The name Ingwenya means Crocodile in isiZulu. Old hats at the IHC Dredgers shipyard will vividly remember the building of the INGWENYA (then H.R. Moffatt) in 1981. Not only because of her nearly perpendicular bow , which recalls famous ocean steamers and battleships, but in particular because of her stationary bow pipe and its housing. The INGWENYA and her sister-ship PIPER are perhaps the only two TSHDs in the world with this feature. The INGWENYA has a centre well in the fore ship that houses the bow pipe and its special lifting system comprising three hydraulic cylinders and multiple sheave blocks. A wire 1 that is led over these sheaves multiplies the stroke of the cylinders, creating enough lifting capacity to allow stationary dredging at a maximum depth of 26 metres. The bow pipe is operated from a separate control cabin in the fore ship, another special characteristic. The specific circumstances in South African ports, TNPA’s desire to be self-sufficient, and the nature of the resulting operations make this bow pipe a useful addition to the normal fittings on hopper dredgers.
In 2008, TNPA Dredging Services started on the implementation of an Asset Replacement Strategy for its floating assets. The plans matured in close consultations between TNPA and IHC Merwede’s Renovation Department. They focused on improvements to the dredging process and dredging performance and so it was decided to concentrate on four main issues:
• Overhaul of the hydraulic installation.
• Replacement of the overflow flaps to port and starboard with a central conical overflow duct.
• A modern, computer-controlled,integrated control system to replace the old dredge process control and its discrete components.
• Replacement of the two density measurement units with one IHC integrated density/velocity transmitter in the common discharge line.
IHC Renovation Sales Engineer Henk Scholten conducted the inspection of the ship. IHC Renovation Project Manager Ron Verschoor coordinated the retrofit and powered up three other IHC Merwede Business units: IHC Hytop for the refurbishment of the hydraulic installation, IHC Parts & Services for the production and installation of the new overflow duct, and IHC Systems for the modernisation of the instrumentation and control system. The first stage of the project included the production of all the equipment involved, and preparations on board.
The hydraulic system is essential for a dredger to perform well. It is the system that powers linear and rotating movements requiring large forces: the sluice valves, swell compensators and many others. TSHDs are crammed full of systems like this. At the training centres of European dredging contractors, operating hydraulic systems is almost the first step in training for would-be dredging operators. Without a knowledge of hydraulics, nobody can operate a dredger. Inspections showed that a large part of INGWENYA’s hydraulic system needed maintenance to remain in operation, and that some other parts had be replaced in their entirety. IHC Hytop took on the job and overhauled the system. This led to a happy blend of old and new components . The fit-to-purpose solution generated major benefits for all parties, saving money, avoiding assembly difficulties and cutting down on delivery time, safeguarding the quality of the installation and extending its lifetime.
Compared with the older side-mounted overflow flaps, the central conical overflow duct from IHC Parts & Services reduces eroding surface overflow streams and drains off the overflow water under the ship. The result is a smaller plume than with the traditional flaps. This is important in today’s dredging, where environmental considerations require reductions in turbidity. Another benefit is the continuously controllable range of this duct, which is considerably larger than that of the old flaps: it can vary from 40-100% of the hopper volume. If correctly operated, this feature allows dredging in shallower locations and helps to reduce losses. During the development stage of the project, TNPA representatives, who are used to controlling dredgers with discrete components and to presentation with individual instruments, were informed about IHC Systems’ modern integrated control systems as used on modern hopper dredgers. They were impressed by how these systems present the dredging process clearly in the light of the prevailing operational method, and decided the INGWENYA had to benefit from this development. So IHC Systems produced the necessary PLC cabinets and SCADA (supervisory control and data acquisition) systems, including dedicated keyboards and colour touch screen video units. PLCs do the signal processing; the SCADA system functions as the Human Machine Interface, providing presentation pages and processing operator commands. Communications between PLCs and PCs are easily established. The advantage of an integrated system of this kind is that input and output signals can be connected to any part of the system anywhere.
The system takes them wherever they are needed, be it as discrete signals or as internal values for processing. Only one cable is required between locations on the ship, or two where redundancy is required. Process data, which did not used to be available to subsystems, can now be applied to interactions between systems. This alone enhances performance. Last but not least, presenting entire processes in a single page dedicated to the current operational stage gives operators a better view of the process itself than ever before, making their job more enjoyable and enhancing confidence. Integrated PLC/SCADA systems are thoroughly tested using IHC Systems’ simulators (see previous issues of Ports and Dredging) as routine. This testing approach prevents hundreds of mishaps on board the vessel during the commissioning stage and speeds up the commissioning process.
After the equipment was shipped to Durban, the second stage began in February 2009: INGWENYA was taken to TNPA’s own dry dock in Durban. As the dredger was being prepared for the modification, new components could be easily installed and commissioned under the supervision of IHC Merwede personnel. In the course of the work, a lot of maintenance proved necessary on the dredging instrumentation, which generates essential input for the SCADA system. The systems installed included brand new stand-alone STPM and DLM systems for the monitoring of the suction tubes and the loading/unloading process. Once everything had been cleared, and once the systems had been commissioned, the INGWENYA completed successful sea trials in July 2009. At the time of going to press, she is actively dredging again, this time to modern standards: efficiently and to the full satisfaction of TNPA. This fit-to-purpose modernisation demonstrates how IHC Merwede’s Life Cycle Support strategy helps clients to maintain peak performance, even with vessels that are nearly thirty years old. But that is not the end of the story…
Construction of TSHD ISANDLWANA
As the upgrade of the INGWENYA was under way, TNPA was engaged in a tender procedure for a third, modern trailing suction hopper dredger. The tender was won by IHC Merwede, and the ship is under construction at IHC Merwede’s VSH slipway in Heusden under yard number CO 1256. After launching, she will be completed at IHC Dredgers in Kinderdijk for delivery at the end of 2010. A full description of the vessel will appear in a future issue of Ports and Dredging. For the meantime, a short preview: The CO 1256 is a twinscrew trailing suction hopper dredger with controllable pitch propellers in fixed nozzles. The vessel is nearly 85 metres long. An additional, electrically driven, bow thruster will ensure good manoeuvrability. The bridge and the accommodation are concentrated in the forecastle; the pump room and the engine room have been located in the aft ship, with the hopper and the suction inlet in between. The automated engine room is suitable for unattended operation. Two main diesel engines, a dredge pump diesel engine and two generator diesels supply energy. Two 3x400VAC main electric systems, one 230VAC 50 Hz system for lighting and civil use and two 24VDC systems supply the electric consumers. Of course, the ship will have modern navigation equipment, an appropriate HVAC system and general service equipment.
The dredging installation comprises one trailing suction pipe to starboard, with a jet-water pipeline providing pressurised water to the nozzles in the excavatingtype draghead. The suction pipe is operated with remotely operated, hydraulic winches and gantries. During loading, a telescopic overflow duct controls the vessel’s draught. The ship can be unloaded using 10 conical bottom valves, or discharge the load through a bow connection or a rainbow pipe. There is a longitudinal self-emptying system with hydraulically operated suction channel doors for rainbowing and discharging, while breaching of the load is facilitated with a hopper diluting system with nozzles in all hopper sections, that are fed by two jet pumps. The jet pumps are direct driven.
The direct-driven IHC high efficiency single-walled dredge pump with its fourbladed impeller is driven via a twin input/single output two-speed reduction gearbox. During trail dredging, the dredge pump diesel engine powers the pump. The starboard main diesel engine provides additional power for shore discharging or rainbowing. A degassing system protects pump and pipelines.
The dredging process is remotely controlled with the proven Dredging Control System (DCS) of IHC Systems. This semi-integrated system, which is based on PLC signal processing and PC/SCADA, makes it possible to control the entire system with keyboards and display units. Pre-programmed process pages, service pages and diagnostic pages on colour video display screens generate rapid overviews of the whole process that are linked to the current operating mode. Keyboards feature the intuitive control of individual and combined functions. The DCS communicates with a host of instrumentation, including the familiar DTPS, STPM and DLM monitoring systems, as well as hopper volume and dry solid mass measurements, ALMO, automatic draghead depth control and, of course, the basics such as mixture pressure, density and velocity measurements. A similar system controls the machinery installation. These systems and the communications between them make for easy interaction between the dredging process, the machinery, and the hydraulics and electrical installations.
The new vessel will be known as the ISANDLWANA, a Zulu word meaning “like a home”, which is what she will be for her crew. The name is also a reference to an important event in South African history. On 22 January 1879, a Zulu army equipped with iron spears and cow-hide shields defeated a British army equipped with modern repeat rifles and artillery at Isandlwana, a location some 200 kilometres to the northwest of Durban. However, the lost battle led to an intensification of the British strategy and, ultimately, the Zulus’ technological disadvantage meant they were subjected to British imperial rule after all. The INGWENYA and ISANDLWANA break with that pattern: these IHC Merwede vessels will provide TNPA with state-of-the art dredging technology, allowing the company to operate at the cutting edge of South African dredging.
Source: IHC Merwede / P&D Magazine, June 24, 2010