The Mooring Selection Guide (MSG) software

Recent Canadian Coast Guard (CCG) buoy mooring maintenance practice includes the retrieval and replacement of mooring chains, on an annual basis, for many coastal buoys. To reduce maintenance costs, a design process was developed at Fleet Technology Limited (FTL) to identify coastal buoy mooring configurations capable of providing up to six years of uninterrupted service. This mooring chain size and configuration selection process has been computerized to form the “Mooring Selection Guide” software. The development of this software, sponsored by the Canadian Coast Guard Marine Navigation Services group and the Transportation Development Centre of Transport Canada, will provide an extended service life mooring design capability to the coast guard bases in a windows compatible software. The design process, described in this paper, compares the buoy and mooring line hydrodynamic loads with the residual strength of the worn mooring chain and transitional resistance of the mooring sinker. The hydrodynamic load effects are estimated for a set of design environmental conditions using the NRC developed MOORDYN code and used to generate response surfaces for the tension in the mooring chain at the sinker, riding and thrash chain sections. The corroded/worn geometry of the riding and thrash chain sections of the mooring system are predicted based on a semi-empirical mooring system wear model which considers nominal chain diameter, mooring depth and duration of service. The residual strength of the mooring system at the highest wear location within the riding and thrash chain sections is calculated using an analytical model based on the deformation of curved beams related to a Von Mises failure criteria