Collision Avoidance for Deepwater Floating Systems: Report of the NOSAC Subcommittee
Authors: Hill Peter J. , Crabtree Sara V. , McDonnell Robert 
Published: October 2008

Abstract
In October 1997 the Shell Mars Tension Leg Platform (TLP) was nearly struck by an 809-foot tankship, the M/V Stavanger Prince. The National Offshore Safety Advisory Committee (NOSAC), sponsored by the U.S. Coast Guard, appointed a special "Subcommittee on Collision Avoidance" to study the incident, review the adequacy of safeguards employed and identify any additional measures that could reduce likelihood or consequences of a large ship collision with an offshore facility. The Subcommittee was to make recommendations for implementation of such measures through new regulation, policy, or voluntary means.
A ship collision with a deepwater floating facility presents a high potential for a catastrophic event. The findings of the NOSAC Subcommittee on Collision Avoidance present alternatives for the reduction of this risk. The expansion of offshore development into deeper waters presents both opportunities and risks as operators tackle new facility types that incorporate more vessel-like features.
Conclusions and recommendations of this paper are drawn from reports of the NOSAC Subcommittee on Collision Avoidance. Additionally, this paper will summarize other governmental and industry initiatives and attitudes concerning collision risk that are related to, but are outside the scope addressed by the Subcommittee. Many of the results presented are under consideration for rulemaking or voluntary compliance initiatives by industry. It is anticipated that presentation of these issues through OTC will facilitate greater understanding and participation by both offshore operators and maritime interests.

Introduction
Deepwater production facilities in the Gulf of Mexico have a greater potential exposure to loss resulting from common hazards than their shallow water counterparts. Among the risk factors that differentiate deepwater facilities are:larger production volumes,higher capital investment,higher sensitivity to hull or support structure integrity,larger crews,more complex operations (drill while produce, etc),and greater distance from shore.
The combination of more costly facilities, higher production flowrates and greater concentration of volumes at hub facilities necessitate a new perspective on the role of ship collisions in the overall risk exposure of a deepwater facility. Simply stated, as produced volume and throughput increase, ship collision events emerge as a dominant component in analysis of risk factored costs, due to the overpowering cost of lost production. Although admittedly a low-frequency event, a serious collision with a deepwater facility could easily result in asset damage, lost production and safety and environmental impact in the hundreds of millions of dollars. With this potential for very large losses, those operating facilities and vessels in the Deepwater Gulf of Mexico must work to better understand the risks associated with collisions and other significant hazards impacting these facilities in an effort to identify ways to reduce their exposure to loss.
This paper presents an overview of the work done by the NOSAC Subcommittee on Collision Avoidance to better define the contributors to and magnitude of collision risks at deepwater facilities in the Gulf of Mexico. The potential impacts of vessel mechanical failures, navigational factors, communication practices and human error were examined. Practices employed in the North Sea were also taken into account, with the recognition that these environments differ significantly with regard to facility congestion, prevalent weather patterns, and the extent to which the coastal states have sought to control vessel traffic.