Introduction
From the 1960’s onwards, there have been continually evolving developments in the size and complexity of oil and gas carrying vessels. This has resulted in the need for terminal owners to pay far more attention to potential risk factors when planning to handle these larger ships. Typically these would include:
• Possible damage to berths and dock structures during docking and whilst moored, due to tides, prevailing winds, wash from passing vessels, etc.;
• Environmental pollutions caused by ruptured loading facilities, cargo tanks or bunker tanks in the event of any collision with dock structures;
• Major risk of fire, particularly in the case of crude, product or gas carriers;
• Dry docking of vessels for inspection or repair following any collision; and
• Insurance/demurrage implications in the event of any accident/damage.
Many terminals were simply not designed to accommodate such large vessels, and their owners faced the prospect of having to invest large amounts of capital into rebuilding and upgrading existing facilities. However, the introduction of the berth management system meant that the risks outlined above could be reduced to a safe and acceptable level and resulted in larger vessels being permitted to berth in smaller terminals. Even in the larger terminals however, berth management systems have been installed as they significantly improve terminal efficiency by enabling vessels to dock in more extreme weather conditions.
History of berth management systems
The first mooring load monitoring system was developed by Strainstall in the early 1970’s for Esso Slagen in Norway. It used strain-gauged load measuring pins (which had recently been developed by the company) as the sensor installed into the quick release hooks to measure the tension in the mooring line (see Figure 1). Further upgrades to the system were made, but the biggest advances occurred when the PC became widely available and applications software became more sophisticated.
In 1990 Strainstall designed and installed the then most complex turnkey Berth Manager system into a coal terminal in Hong Kong. This included mooring load monitoring on 3 jetties, integrating with existing sonar-based speed of approach measurement, environmental and meteorological sensors, carry-on-board laptop shipboard repeaters on radio telemetry links and fibre optic links to remote stations in the facility. A total of 13 computers were networked and interlinked to provide a fully integrated system which presented the terminal operator with a full set of ship behaviour data and associated environmental forcing functions. Development of networkable digital conditioning followed, allowing jetty sensors and displays to be connected by a single cable loop, which provided significant cost savings to the client in the supply and installation of site cables. At the same time developments in the measurement of speed of approach were tending to favour radar or lasers over sonar, with eye-safe lasers becoming the measurement sensor of choice for providing the most accurate and reliable data in all conditions likely to be encountered during a docking operation.
More recent developments
There is however a restriction in using this method, as these lasers are only able to monitor the vessel when it is perpendicular to the jetty. In order to offer a speed of approach package suitable for front-end docking, an additional docking measurement system has recently been developed using Differential Global Positioning System (DGPS), which provides centimetre accuracy. This also expands the ability to provide a small vessel traffic management capability, as it is able to monitor the approach of the vessel from a much greater distance from the jetty and from any direction – in effect from when the pilot boards the vessel. The basic system requires two DGPS sensors to be positioned onboard the vessel and a base station on the jetty. A palmtop can also be provided for the pilot to carry on board that presents him with continuous speed-of-approach during a docking.
Data display
A number of options are available to display the speed-of-approach data outside the control room. These include large digit displays and traffic lights that are mounted on the jetty and are visible for up to 200 – 250m, for use by the approaching vessel (see Figure 2). These are available for safe or hazardous areas and provide the pilot with numbers in an ergonomic heads-up manner. Pagers are also available for the pilot and/or shore based docking crews, and remote displays on the jetty for use by the shore based docking crews.
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