Engineering methodologies used in the preparation of escort tug requirements for the ports of San Francisco and Los Angeles/Long Beach

The assumptions made and methods used to prepare the selection matrix for e scort tugs that is incorporated into the California statute for the ports o f San Francisco and Los Angeles/Long Beach are presented. The default matri x for both ports is based on a demand/capability analysis. The demand is a function of (a) port geometry; (b) operational practices, including transit speeds, tethering, failure modes, and failure recognition times; (c) emerg ency maneuver (stopping and/or turning of the disabled vessel); and (d) shi p size. The capability is defined as the total bollard pull of the escortin g tug or tugs. An escort is acceptable if the capability exceeds the demand . The assumptions and rationale used in the calculation of demand and the c hoice of bollard as capability, the differences in the demand function for the two port complexes, and the differences in the rationale for the bollar d pull capability at the two port complexes are explained. There is an opti on for alternate compliance in San Francisco that is based on the fact that tug capability may be greater at the transit speed than it is at bollard. The procedure and difficulties with this approach to maintain compliance wi ll be described. In LA/LB there is also an option for alternate compliance. However, alternate compliance in LA/LB is based on tethering and deploymen t of the escorting tugs, The rationale for the different alternate complian ce calculations for the two ports will be explained.