This is displayed e.g. in Figures 7 and 8: it is observed that at 40 kn, a change of heading of 30 degrees results in an at least 10% reduction of motions and loads while passing from 40 to 35 kn. results in a reduction of some 20%.
4. CONCLUSIONS
In this paper, the importance and usefulness of seakeeping analysis for the design of passenger ships is highlighted and demonstrated through two practical applications.
In both cases seakeeping analysis proved to an effective tool for determining both design loads and operational recommendations for special ships types which, in view of their characteristics, can not be successfully dealt with by traditional semi-empirical formulations.
Additionally, the following comments are worthwhile:
a) Scientific research.
Considerable R&D effort are underway world-wide with the aim of improving the capability of modern seakeeping tools to account for non-linear effects; an excellent survey is provided in [8]. Although these efforts are most welcomed, significant results can be obtained by properly using linear strip theory in combination with experimental results with significant benefits for designers: reducing the extent of model tests and being able to extrapolate their results to cover different design scenarios.
b) Classification rules.
Rules of Classification Societies are normally used to fix the design basis of new buildings. In recent years, direct calculations have been introduced into Rules both as the basis for calibration and as an alternative to rule checking formulas. In this respect the use of seakeeping models is increasing and will more and more increase in the future in particular for the design of ships of high added value such as passenger ships. RINA Rules 2000 [9] recently entered into force, are an example of Classification Rules open to a wide use of direct calculations and seakeeping analysis.
c) Operational aspects
The most interesting application of seakeeping is however likely to be, in the near future, related to the possibility to provide the ship master with ad hoc suggestions and indications on the best course keeping and ship speed in relation to the severity of the surrounding environment. Times are now mature for the development of simplified on-board monitoring systems providing information to the ship master for optimal ship seaworthiness. This is of particular relevance for ships having high passenger comfort standards such as high speed craft and large cruise ships.
5. REFERENCES
[1] Juncher Jensen J., Terdrup Pedersen P., "Wave induced Bending Moments in Ships- A Quadratic theory", Trans. RINA, Vol. 121, pp 151-165, 1979.
[2] Juncher Jensen J., Bamke L., Dogliani M., "Lon term Predictions of Wave-induced Loads using a Quadratic Strip Theory", Proceeding Int. Cof. On Ships and Marine Research (NAV 94), Rome October 1994.
[3] Wang, Z., Folsφ, R., Bondini, F. and Pedersen, T., "Linear and Non-Linear Numerical Sea-keeping Evaluation of a Fast Monohull Ferry Compared to full Scale Measurements". Proceedings of FAST99 International Conference on Fast Sea Transportation.
[4] Faltinsen O. M., "Slamming on ships", Proceedings of IMAM 2000 Congress, Ischia (Italy) 2-6 April 2000. Vol. I pl3
[5] Ship Structural Committee. "Hydrodynamic Impact on Displacement Ship Hulls - an Assessment of the State of the Art", SSC Report n. 385, January 1996.
[6] Dogliani M. "EUROSLOSH Project - Numerical and Experimental Analysis of Sloshing in Tanks" Final Report for the European Commission, RINA 1994 (Confidential)
[7] Monti S., Grossi L., "Definition of a Monitoring System to Collect Structural Data on New Fast Ship in Service", Proceeding of the HSMV 99 Comference, Vol. 1 , Capri 1999.
[8] The International Ship and Offshore Structures Congress (ISSC) 2000, Report of Technical Committee 1.2 "Loads", to be presented at the ISSC 2000, Nagasaki, Japan, 2-6 October 2000.
[9] RINA Rules for the Classification of Ships, Ed, 2000, l June 2000, Genova
TABLES
Table 1 - Experimental vs. theoretical values of Cpmax
