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Fig. 17 Scatter plot between the measured overshoot angles and the calculated swept-path indices.
(a)10°/ 10°zigzag 1st OVS vs. SI from 10°bent seaway
(b)10°/ 10°zigzag 2nd OVS. vs. SI from 10°bent seaway
(c)20°/ 20°zigzag 1st OVS vs. SI from 10°bent seaway
(d)10°/ 10°zigzag 1st OVS vs. SI from 30°bent zigzag seaway
(e)10°/ 10°zigzag 2nd OVS vs. SI from 30°bent zigzag seaway
(f)20°/ 20°zigzag 1st OVS vs. SI from 30°bent zigzag seaway
In this sense, we think that the criterion on the second overshoot angle for 10°/10°zigzag test in necessary.
CONCLUSION
In this research, we tried to find a correlation between the overshoot angles and the navigational difficulty. For this, sea-trial data and detailed information for the recently built forty tankers were collected and analyzed. And navigational difficulties of these ships were evaluated by adopting rudder index and swept-path index. These indices were calculated from the auto-tracking simulation in the artificial seaways. Through these, we can arrive at the following conclusions.
1. The simple manoeuvrability indices, such as KT or PKT, do not clearly show their relationship with the overshoot angles and tactical diameter.
2. By the numerical simulation of manoeuvring motion, we can reconfirm that the overshoot angles are closely related to the spiral loop width and height, and they can be used as a good index for yaw-checking ability. Specifically, characteristics of the spiral loop show very close relationship with the 1st overshoot angle of 10°/ 10°zigzag manoeuvre.
3. Sea-trial results show that more than 30% of the small ships, whose length is between 100 and 200 meter, do not satisfy the IMO resolution on the 1st overshoot of zigzag test even at trial draft. Considering that those ships are successfully delivered and being normally operated without trouble report on their manoeuvrability, the resolution seems to be a little bit severe for the smaller ships.
4. Navigational difficulties, evaluated by the rudder index and the swept-path index from the auto-tracking simulation, show that the navigational difficulty is closely correlated with the 2nd overshoot angle of the 10°/ 10°zigzag test. So both 1st and 2nd overshoot angles are necessary for the discrimination of ships manoeuvrability.
5. It seems to be necessary to review the IMO criterion on the overshoot angles, which is defined as a varying function of L/U. In one sense, it may have a meaning that a ship with the smaller L/U should keep the severer overshoot criteria, because those ships are usually small ships under 200 meter in length, and they are usually navigate the costal area where the possibility of marine casualty is high. Furthermore, the parameter L/U plays an important role in the determination of spiral loop height. However, considering that navigating small ships is at least 20% less difficult than the large ones, and those ships are normally operated without problem, the IMO criterion seems to be alleviated.
REFERENCES
[1] IMO, "Resolution A.751(18), Interim Standards for Ship Manoeuvrability", 1993
[2] IMO MSC 71/20/9, 1999
[3] IMO DE 44/wp.3, "Revision of the Interim Standards for Ship Manoeuvrability", 2000
[4] IMO DE 45, 2001
[5] IMO MSC 76/23, "Resolution MSC.137(76), Standards for Ship Manoeuvrability", Report of the Maritime Safety Committee on Its Seventy-Sixth Session-Annex 6, 2002
[6] Katsuro Kijima, Yasuaki Nakiri and Yoshitaka Furukawa, "On a Prediction Method for Ship Manoeuvrability", Proceedings of the CPMC 25, paper7, 2000
[7] The Manoeuvring Committee, "Final Report and Recommendations to the 23rd ITTC", Proceedings of the 23rd ITTC - Volume I, pp.164〜167, 2002.
[8] Kyoung-Ho Sohn, S. Y Yang and D. S. Lee, "A Simulator Study on Yaw-checking and Course-keeping Ability in IMO's Manoeuvrability Standards", SOTECH Vol. 6, No. 3, pp.26〜36, 2002
[9] Yoshimura Y. and Kose K., "Studies on the Manoeuvrability Standards", Proceeding of 19 th ITTC, pp.569-570, 1990.
[10] Key-Pyo Rhee, S. Y. Kim, N. S. Son and Y. J. Sung, "Review of IMO Manoeuvring Standards in View of Manoeuvring Sea-trial Data", Proceeding of Mini Symposium on Prediction of Ship Manoeuvring Performance, pp.1〜10, 2001
[11] In Young Gong, et.al, "Development of Safety Assessment Technologies for Tanker Route (I): Appendix E", KRISO Report, UCNO31-2057.D, 1997 (Korean).
[12] Thor I. Fossen, "Guidance and Control of Ocean Vehicles", John Wiley & Sons, pp.259〜263, 1994
[13] Nomoto K., "Some Aspects of Simulator Studies on Ship Handling", Proceeding of PRADS, pp.303〜310, 1977
[14] IMO DE 45/3, "Proposal for the Revision of the Interim Standards for Ship
Manoeuvrability-Annex 1 ", Yasuo Yoshimura, "Investigation into the Yaw-Checking Ability in Ship Manoeuvrability Standards", Proceeding of Mini Symposium on Prediction of Ship Manoeuvring Performance, pp.11〜49, 2001
AUTHOR'S BIOGRAPHY
K. P. Rhee graduated with Dr. of Engineering degree in Naval Architecture from Seoul National University in 1977. He also obtained his B.S. and M.S. degrees from the same university. After graduating, he has been worked at the Dept. of Naval Architecture and Ocean Engineering, SNU since 1978, and is presently a full professor. His research and publications are in the area of the sea-keeping, manoeuvring, control and system identification of dynamic motion of various types of surface and underwater marine vehicles, and he has authored about 70 technical papers and reports on these area.
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