Tanker Escort-Requirements, Assessments and Validation

Tanker escort practice varies throughout the world and is usually based on a local perception of need and adequacy that is rarely backed up with a rigorous analytical assessment or field trials.. In the United States, the Oil Pollution Act of 1990 (OPA '90) has empowered the US Coast Guard (USCG) to set up new regulations for tanker escort, specifically in the waters of Prince William Sound and Puget Sound. State rules also exist such as for Puget Sound and San Francisco Bay to regulate tug escort of tankers. In this paper, the escort requirements of specific waterways are presented with special emphasis on escorting in Prince William Sound, San Francisco Bay and Puget Sound. A summary of escort practice in Europe is also provided. Two methods for examining and specifying tanker escort requirements are detailed in this paper. The first method is an operations analysis strategy, that examines a specific escort practice such as a tanker-tug combination and determines the boundaries of its applicability. The procedures of this method are applied to the analysis of tanker escort on Prince William Sound. The second method is a systems analysis approach that is oriented towards a rule-making process. In this case the "demand" of a disabled tanker for tug assistance is quantified as a function of displacement, speed, weather and waterway constraints. The application of this methodology to San Francisco Bay is detailed. Both methods make extensive use of computer simulations for tanker maneuvering with tug assistance in a given climatology. A statistical procedure to define the geographical constraints of the waterway is introduced. USCG rules for tanker escort on Prince William Sound and Puget Sound are reviewed and their interpretation and application discus sed in relation to Puget Sound.