# Effect of bilge keels on maneuverability of a fine ship

## Abstract

This paper discusses the effect of bilge keels on maneuverability of a fine ship experimentally and theoretically. To capture the effect, first, free-running model tests were conducted using a KCS container ship model with detachable bilge keels. We found that bilge keels improve the turning performance and enlarge overshoot angles in zig-zag maneuvers, and that this tendency becomes more pronounced with increasing ship speed. Next, captive model tests were conducted to capture the hydrodynamic forces’ effects on maneuvering to clarify the reason for the difference in maneuvering in the presence of bilge keels. By attaching bilge keels, the absolute values of \(Y_v'\), \(N_v'\), and \(K_v'\) (the linear derivatives of lateral force, yaw moment, and roll moment acting on the ship with respect to lateral velocity *v*, respectively) are increased and \(Y_{\phi }'\) (the derivative of the lateral force with respect to roll \(\phi\)) is also increased. It can be explained theoretically that the change of the hydrodynamic derivatives leads to course instability according to the course stability criterion presented by Yasukawa and Yoshimura [3]. The special feature of the criterion is to include the roll-coupling effect. Thus, the roll-coupling significantly affects ship maneuverability through hydrodynamic derivative changes by attaching bilge keels to fine ships with small metacentric height \(\overline{GM}\).

## Keywords

Bilge keels Ship maneuverability Captive model tests Free running tests Course stability## Notes

### Acknowledgements

This study was inspired through discussions with Dr. F. Quadvlieg of the Maritime Research Institute Nederland (MARIN), and we would like to express our thanks to him. We would like to extend our thanks to Dr. A. Matsuda and Dr. D. Terada of the National Research Institute of Fisheries Engineering, Japan, and Mr. S. Mizokami and Mr. R. Kuroiwa and their staff of the Seakeeping and Maneuvering Basin at the Nagasaki R & D Center, Mitsubishi Heavy Industries, for their help with the tank tests. This study was supported by JSPS KAKENHI Grant no. JP26249135.

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