5.2 Sea Trial Data

　

　

　

　

5.3 Analyze and Discussion

　

1) Compared with the sea trial data, the accuracy of the simulation results are generally acceptable for engineering application, which indicates that it is successful to replace the waterjet propulsions by the rotatable propellers and to adjust some hydrodynamic derivatives at different speeds.

　

2) Fig.5 shows that in 30° zig-zag test with engine RPM at 1940 the first overshoot angle is larger than the later ones, which is conform with the sea trial data. The comparison between Fig.5 and Fig.6 indicates that the overshoot angles are usually larger at higher engine RPM.

　

3) From Fig.8 and Fig.9, it can be seen that the turning circle is smaller at higher RPM under the same deflection. The reason may lie in the fact that side thrust force is larger, although the ship is approaching at higher speed. As shown in Fig. 10, even without jet deflection, the differences between the thrust of two jets can provide considerable manoeuvring force as expected.

　

4) The decrease of ship speed is acute during the initial turning stage at full speed. This decrease reaches up to 40% of the approaching speed, while the lateral speed increase amounts to 25% of the speed, and the non-dimensional value of yaw rate 0.6 during stable turning stage. Compared with the experimental results presented in Reference [12], the changes in speed and yaw rate look quite similar in trend. On the other hand, traced back to the deviation of turning diameter between simulation result and the sea trial data shown in Fig.8 and Table 3, r = 6.0 may be a bit smaller than that should be.

　

5) As shown in Table 4, the stopping distances both simulated and measured are no more than 1.6L, and the time less than 15 seconds, which demonstrates that the reverse thrust plays the most important role in the braking. On the other hand, as shown in Fig. 11, the speed increase at acceleration only takes about 50 seconds to get full speed. Consequently, it is safe to say that waterjet propelled catamaran is excellent in the accelerating and braking.

　

6) Because the sea trial was conducted under the condition of calm water and no wind, the simulation results with environmental effects are partly given without comparison.

　

 This paper presents a mathematical model of manoeuvring motion for waterjet propelled catamaran, where rotatable propellers are substituted for the waterjet and the hydrodynamic derivatives estimated and amended in term of the speed. In addition, environmental effects including wind, wave, current and water depth are taken into account and processed in the conventional way.

　

 The simulation results of ship motion have been validated by a proper comparison with sea trial data and the following conclusion may be drawn.

　

1) From the viewpoint of engineering, the proposed mathematical model is satisfactory and practical.

　

2) The equivalence of propeller for waterjet propulsion is effective and practical.

　

3) The hydrodynamic derivatives amended according to speed are reasonable.

　

4) In order to get better simulation results, it is necessary to find better expressions for the hydrodynamic derivatives and the waterjet characteristics. In addition, a 4 DOF model is also requested.

　

 The work presented in this paper is financially supported by the Ministry of Education of China and the National Natural Science Foundation of China under the Grant No.10272085.

　

[1] 21st ITTC Manoeuvring Committee "Final Report and Recommendations to the 21^st ITTC, Trondheim, Norway, pp. 347-399, 1996

[2] Austal "Catamaran Manual, Appendix C: Sea Trial Manoeuvring Data"

[3] Guohua Song "Catamaran Design" (in Chinese), Boats, pp. 32-46, 1998. 1, pp. 39-45, 1998.2, pp.36-44, 1998.3.

[4] http://www.austal-ships.com.au/

[5] Jiaxin Wang "Menoeuvrability of Catamaran Propelled by KaMeWa" (in Chinese), Journal of Water Transportation in China, pp. 28-29, 2000.11

[6] John Allison "Marine Waterjet Propulsion" SNAME Transaction, pp. 275-335, 1993,Vol. 101

[7] Juehua Yan, et. al. "Catamaran in the Inland Waterways (in Chinese), People's Communication Press, pp. 189-190, 1980

[8] Katsuro Kijima, Yasuaki Nakiri, Yasuharu Tsutsui "Prediction Method of Ship Manoeuvrability in Deep and Shallow Waters", Proc. of MARSIM & ICSM'90, Japan, pp. 311-318, 1990

[9] KunJin Kang, SunYoung Kim, YoonRak Choi "Seakeeping and Maneuvering Performances of the 2,500 Tons Class Trimaran", Proc. of Workshop IWSH'2001, Wuhan, China, pp. 38-44, 2001

[10] MARIC "Collection of Papers on Ship Waterjet Propulsion" (in Chinese). MARIC, 1999

[11] Paul Kaplan, Jens U. Römeling, Trond Tveit "A Hydrodynamic-Based Simulator for Fast Ship Manoeuvrability Assessment and Training", Proc. of FAST'95, Germany, pp. 379-393, 1995

[12] Pierre Perdon "Rotating Arm Manoeuvring Test and Simulation for Waterjet Propelled Vessels", Proc. of Symposium MAN'98, France, pp. 41-46, 1998

[13] Qinsheng Mei "Application of Burill-Gawn Propeller" (in Chinese), Jiang Su Shipbuilding, pp. 17-21, 1991.2

[14] S. Brizzolara, L. Gross, S. Chislett "Course Keeping Aspects in The Design of Fast Deep-V Monohulls", International Conference on High Speed Craft Motions & Manoeuvrability, Paper 6, RINA, England, 1998

[15] Tsuyoshi Ishiguro, Kenji Uchida, Takashi Manabe "A Study on the Maneuverability of Super-slender Twin Hull", Proc. of FAST'93, Japan, pp. 283-294, 1993

[16] Yansheng Yang "Study on Ship Manoeuvring Mathematical Model in Shiphandling Simulator", Proc. of MARSIM'96, Denmark, pp. 309-318, 1996

[17] Zhian Hu, Jieya Li "Some Problems of Propeller Design for High Speed Ship" (in Chinese), Journal of Ship Design, pp. 12-19, 1995.4

　

 Junmin Mou: Ph.D. course student in Wuhan University of Technology, China. His previous research experience includes ship maneuvering simulation and the safety of navigation.

　

 Zaojian Zou: Prof. Dr-Ing., is Head of the Institute of CFD in Ship and Ocean Engineering, Wuhan University of Technology, China. His research interest includes prediction of ship maneuverability, calculation of hydrodynamic forces on maneuvering ships and CFD in ship design.

　

 Xiaotu Zhang: Postdoctor at State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, China. His previous research experience includes ship maneuvering simulation and CFD in ship and ocean engineering.