An efficient method to assess effect of fin on the course stability of towing system

Abstract

Some new-built ship-shaped offshore structures like FPSO or FPU are found to show insufficient course stability due to rough design, which makes the towing operation hazardous. This paper aims at investigating the stern fin as a proposed solution for improving the poor course stability of a FPSO in towing operation by creating a practical approach. The fin’s hydrodynamic lift coefficient is predicted by the vortex lattice method. The numerical towing system is of three degrees of freedoms and accounts for hydrodynamic forces, the interactions acting on the hull and other appendages, as well as the towing line. Various hydrodynamic derivatives are considered linear and estimated by the empirical method. The configurations of single fin, double fins, and twin fins, as well as the influence on towing stability, are studied. In particular, the hydrodynamic interaction of twin fins, lift coefficient reduction and the impact of spacing are analysed. Different stable and unstable behaviours in the time domain are observed and discussed in depth. The eigenvalue analysis is conducted based on the linearized towing system.