There is a delicate balance that must exist between the aerodynamic, hydrodynamic, and mooring forces acting on a floating body restrained by a single anchor (single point mooring). If the balance is not achieved, the floating body will exhibit undesirable motions which have been referred to by the industry as horsing, fishtailing, kiting, and “sailing about at anchor.” Significant work related to the offshore oil industry documents these yaw instabilities on single point moorings; however, the knowledge base is not very well disseminated outside of the offshore sector, especially when considering that vessels of all types are susceptible to this phenomenon.
When the aerodynamic forces dominate the hydrodynamic and mooring forces, no matter the vessel type or configuration, the potential for the undesirable motions to occur exists. With the increased desire for larger interior volumes on vessels, hull and superstructure windages are trending larger and the aerodynamic forces acting on the vessels are becoming more significant, making the phenomenon a more common occurrence.
This paper provides an introductory overview to the phenomenon of yaw instability of a vessel on a single point mooring, and documents a technical investigation into the phenomenon. The research program conducted consists of full-scale sea trials, aerodynamic analysis through computational fluid dynamics, numerical simulations, and physical scale model testing. Results of the research program are presented which demonstrate successful replication and mitigation of the motions.
