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Using Passing Vessel Analysis to reduce operational risks

Posted: 30-Oct-2017

Passing Vessel Analysis has a vital role in limiting the operational risks associated with mooring operations

Passing Vessel Analysis is fast becoming an essential requirement in the planning of marine facilities, say navigation simulation and ship mooring experts, HR Wallingford, who have been working in Texas to develop inland waterway facilities that protect moored vessels from passing ships.

In the United States, the amount of waterborne transport completed by inland waterways is significant. In Texas alone, transport by inland waterway accounts for around 600 million tonnes each year, close to 30% of waterborne trade in the entire U.S.A. by tonnage. As waterways continue to develop, many of the prime locations have already been occupied leading developers to look at increasingly more complex sites to locate new marine facilities.

These sites may be on the bend in a channel, or where it is not possible to design traditional ship docks orientated parallel to the main shipping channel, and can be considerably more complex from a marine design perspective. As the average size of the vessels using these waterways has increased notably in recent years, so too has the frequency of mooring line failures resulting from vessels passing too close and / or too fast past ships moored at existing facilities. In recognition of this, local pilotage organisations now require a passing vessel analysis as part of the permit conditions attached to the development of a new facility.

Passing vessel analysis is a fully dynamic ship mooring analysis which systematically considers a range of different conditions, such as vessel draught, speed and separation distance to build a risk profile of potential passing vessel effects at the new facility. It ultimately serves two purposes: to validate the engineering design in terms of berth geometry and capacity of mooring hardware to be installed; and to provide local pilots with guidance on acceptable speeds and passing distances with which they may pass ships moored at the new facility.

“We have gathered data from hundreds of physical model tests to investigate ship mooring response” says Dr Mark McBride, HR Wallingford’s Ships Group Manager, “and this data, along with full scale measurement campaigns carried out by industry, has been used to continually develop and validate our numerical modelling tools against increasingly complex scenarios. For our clients, this translates into the development of optimised marine facilities and a more informed picture of the operational risks associated with passing vessels on the adjacent waterway.”

As ships continue to grow in size, so too comes the need to expand the waterways and provide additional channel capacity. There are already several such projects proposed in Texas and many more across the United States. The introduction of larger vessels in deeper draught channels typically increases the risk of mooring line failure due to passing vessel interaction. Consequently, it is not only important to assess the situation for new terminals, but also to reassess the risks associated with existing terminals.

Of particular relevance in the U.S.A. is the potential interim condition resulting from the sequence in which the U.S. Army Corps of Engineers deepen the Federal Navigation Channel and the private industry operator chooses to deepen the access to its own ship docks, if at all. These changes have the potential to significantly impact the operational risk profile associated with mooring operations at existing facilities, and vessel passing is an issue that some operators are setting out to understand in more detail.

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