The risk of collision with a ship is now estimated to be the single largest source of risk for some North Sea offshore platforms. Current procedures for modelling risk due to passing ships are omni-directional, and no explicit consideration is usually given to the directions in which the ships are travelling relative to the faces of the platform. This paper examines the effect of ship direction upon collision risk through a case study using the COAST database and a simple new collision damage model. It is found that collision damage risk can vary significantly with direction. The paper argues that there could be significant improvements to the current practice in the modelling and estimating of collision risk.
The risk of collision between an offshore platform and a ship is now the biggest component of the total risk for some fixed platforms in the southern North Sea. This risk comprises two elements: the first is from attendant vessels such as supply ships, crane barges and work-over support vessels. The second is from passing vessels involved in cargo transport, fishing and other activities unconnected with the platform. Attendant vessels are usually manoeuvring at low speed in the vicinity of the platform and thus have low kinetic energy. So whilst the probability of collision is relatively high (HSE 2003), the energy and consequently damage involved will be minor and platforms are designed to accommodate such impacts. Passing vessels on the other hand will be travelling at their normal operational speeds and have very large kinetic energies. Any collision is likely to result in significant, and perhaps catastrophic damage to ship or platform or both (e.g. Pedersen 2002). From an offshore operators perspective this presents a major problem because the risk of collision with a passing vessel is largely outwith their direct control.