At Anchor wind induced yaw instability of a monohull

OCTOBER 22, 2019


Jonathan Soja, Donald L. Blount and Associates, Chesapeake, Virginia, USA

Jeffrey Bowles, P.E., Donald L. Blount and Associates, Chesapeake, Virginia, USA


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.

yaw instability single anchor

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.


In case you would like to receive he full paper, or discuss about this subject, please contact Jeffrey Bowles.

yaw instability fishtailing and horsing


1. U.S. ARMY CORPS OF ENGINEERS, “Design: Moorings,” UFC 4-159-03, Sep. 2012.

2. FLORY, J., and PORANSKI, P., “The Design of Single Point Moorings,” 9th Annual Offshore

Technology Conference, 1977.

3. WICHERS, J., “On the Slow Motions of Tankers Moored to Single Point Mooring Systems,” 8th

Annual Offshore Technology Conference, 1976.

4. MALONEY, E., “Chapman Piloting: Seamanship & Small Boat Handling,” The Hearst

Corporation, 2006.

5. NOEL, J., “Knight’s Modern Seamanship, 18th Edition,” John Wiley & Sons, Inc, 1989.

6. OWENS, R., and PALO, P., “Wind-Induced Steady Loads on Ships,” Naval Civil Engineering

Laboratory, 1982.

7. AAGE, C., “Wind Coefficients for Nine Ship Models,” Hydro- Og Aerodynamisk Laboratorium,


8. “DDS 568-1 Thruster Maneuvering Systems,” Naval Sea Systems Command, 1987.

Share this article online:

Share on facebook
Share on linkedin
Share on twitter
Share on whatsapp

DLBA Naval Architects

860 Greenbrier Circle, Suite 201  Chesapeake, Virginia 23320 USA

Phone: 757-545-3700  |  Fax: 757-545-8227  |



Keep your finger on the pulse of the latest points of focus in naval architecture and engineering: subscribe to DLBA’s concise monthly newsletter. Within it, we briefly describe and picture our latest projects and concepts. We encourage feedback and seek to have our newsletter spark conversation regarding potential collaborations and further advancements as we share our passion for the industry.