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Conclusion
3.5
3
2.5
2
1.5
1
0.5
0
(g)
Figure 2: Turning Circle Radius (a) at t = ‐0.5, Reff = 1 (b) at t = ‐0.5, Reff = 1.25 (c)
at t = ‐0.5, Reff = 1.5 (d) at t = ‐0.5, Reff = 1.75 (e) at t = ‐0.5, Reff = 2 (f) at t = ‐0.5,
Reff = 2.25 (g) at t = ‐0.5, Reff = 2.5
It can be concluded that the ship’s directional
stability improves as the trim moves towards
positive values and so do with increasing rudder
and skeg effectiveness. As the ship trimmed
more by the stern (positive trims) and with
increasing rudder and skeg effectiveness, the
wetted surface area of the ship becomes larger.
Therefore by virtue of its position, the centroid
of the wetted surface shifts towards aft, the
directional stability increases. The magnitude of
the stability criteria is an indicative of the degree
of the directional stability. The ship is more
directionally stable with numerically higher
values of stability criteria. The negative values of
the stability criteria indicate that the ship is
directionally unstable. The lower the negative
values of the stability criteria, the more unstable
directionally the ship is. It can be deduced that
the ship manoeuvrability increases with
increasing directional stability, turning radius,
positive trim, rudder effectiveness and skeg
effectiveness.
Skeg Effectiveness
MIMET Technical Bulletin Volume 1 (2) 2010
Turning Circle Radius
t=-0.5, Reff=2.5
-47.67 -73.00 -98.27 -123.48 -148.62 -173.69 -198.70
Turning Circle Radius (m)
References:
1. R.K Burcher (1971) Development in Ship Manoeuvrability,
Royal Institutions of Naval Architects (RINA).
2. Inou, Hirano and Kajima (1981) Hydrodynamic Derivatives
on Ship Manoeuvring, International Shipbuilding
Progress,
Vol. 20.
3. E. C Tupper (2004) Introduction to Naval Architecture, 4 th
Edition, 253‐261.
4. K.J Rawson and E.C Tupper (2001) Basic Ship Theory, Vol.
2, 5 th Edition, 539‐578
5. Toshio ISEKI (2005) Ship Manoeuvrability, Theory and
Assessment, Advanced Topics for Marine Technology by,
Tokyo University of Science and Technology, Japan.
6. Eda H. (1972‐1979) Directional Stability and Control of
Ships in Waves, Journal of Ship Research, Vol. 16, Issue
No. 3, Society of Naval Architects and Marine
Engineers, 205‐218
7. N. Minorsky (2009) Directional Stability of Automatically
Steered Bodies, Journal of the American Society of the
Naval Engineers, Vol. 34, Issue 2, 280‐309
8. Haw L. Wong, Cross Flow Computation for Prediction of
Ship Directional Stability, Hydrodynamics, Theory and
Application, Department of Mechanical
Engineering, University of Hong Kong, Vol. 1, 285‐290
9. B. V. Korvin‐Kroukovsky (2009) Directional Stability and
Steering of Ships in Oblique Waves, Journal of the
American Society of the Naval Engineers, Vol. 73, Issue 3,
483‐487.
10. Ship Factors that affect Manoeuvring, SHIPS SALES.COM
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