Collision and Allision Risk


One of the major accident hazards to which offshore structures are exposed is ship collision (more typically referred to as ‘allision’ in offshore renewables).

Two of the top 20 largest property damage losses in the hydrocarbon industry worldwide between 1974 and 2015 have been caused by vessel collisions (Ekofisk in 2009, $860m; Mumbai High North in 2005, $490m). The latter also resulted in 22 fatalities due to escalation.

Anatec has significant experience and industry-leading risk software in this field (ShipRoutes and COLLRISK), which are cited by the International Oil and Gas Producers Association (IOGP) in the Risk Assessment Data Directory report for Ship/Installation Collisions under “Best practice collision risk modelling for passing vessels” and have been fully accepted by regulators for use in offshore renewables Navigational Risk Assessments (NRAs).

Our models are used on projects throughout the world to assess the risks associated with ship/structure collision (allision) from passing (commercial / fishing) and infield (attendant / visiting) vessels.

The nature of the analysis differs depending on the type of structure and shipping being assessed. For example, for passing ships both powered collisions due to watchkeeper failure, and drifting collisions due to engine failure, are assessed. For infield vessels, the main risks are from Dynamic Positioning (DP) drive-off or drift-off, as well as higher speed collision on approach due to failure to follow procedures.

In all cases, the consequences are evaluated in terms of risk to the physical structure (energy of impact based on the displacement tonnage and speed of the colliding vessel) and to personnel onboard, where applicable.

Anatec’s models are calibrated for the industry and geographical area of interest using the most up-to-date historical accident data available. Most recently our models have been updated based on a review of collision / allision data within oil & gas and offshore wind carried out while preparing guidance on passing vessel collision risk management on behalf of The Energy Institute.

Finally, Anatec’s COLLRISK model also includes software for assessing the risk of vessel-to-vessel collisions, which can be used to model the change in risk caused by a new development such as an offshore wind farm. This is informed by vessel-to-vessel encounters analysis using baseline traffic survey data, as well as simulation of post-wind farm traffic predicted based on stakeholder consultation and maritime experience.


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