Engineering Methodologies Used in the Preparation of Escort Tug Requirements for the Ports of San Francisco and Los Angeles/Long Beach

Abstract

The assumptions made and methods used to prepare the selection matrix for escort tugs that is incorporated into the California statute for the ports of San Francisco and Los Angeles/Long Beach are presented. The default matrix 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) emergency maneuver (stopping and/or turning of the disabled vessel); and (d) ship size. The capability is defined as the total bollard pull of the escorting 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 choice of bollard as capability, the differences in the demand function for the two port complexes, and the differences in the rationale for the bollard pull capability at the two port complexes are explained. There is an option 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 will be described. In LA/LB there is also an option for alternate compliance. However, alternate compliance in LA/LB is based on tethering and deployment of the escorting tugs. The rationale for the different alternate compliance calculations for the two ports will be explained.