Str^m-Tejsen and Chislett 



consequently limited. Whereas an acceptable coverage can be obtained for the 

 6-to-7-metre cargo ship models, the range of yaw velocities which can be ob- 

 tained for the smaller naval ship models is more limited than desirable, except 

 at lower speed values. 



Forces measured in the low-frequency range have been found either inde- 

 pendent of frequency or to vary with frequency but approach steady-state re- 

 sults as frequency tends to zero. 



It is finally concluded that the semitheoretical technique combining planar- 

 motion mechanism model-testing and computer-prediction of manoeuvres allows 

 scaling problems to be treated satisfactorily. Large models can be used in the 

 testing, whereby scale effects in general are reduced. Tests can be carried out 

 at the ship propulsion point by applying a towing force via the rigid connection 

 to the mechanism, the correct propeller rpm being obtained by taking the partic- 

 ular engine type and control arrangement into account. The individual meas- 

 urement of the various coefficients gives an insight into the hydrodynamic phe- 

 nomena involved and consequently allows corrections to coefficients for difference 

 in Reynolds' number for model and ship to be considered. 



ACKNOWLEDGMENTS 



The HyA planar-motion mechanism system was designed and developed 

 jointly by the authors at the Hydro- and Aerodynamics Laboratory in 1962-1964. 

 The authors gratefully acknowledge the inspiration provided by Professor 

 Martin A. Abkowitz during his stay at HyA in 1962-1963; the support of Profes- 

 sor C. W. Prohaska, director of the laboratory; and their deep indebtedness to 

 Hr. Erik Wolstrup Pedersen, who in building and testing the electronic instru- 

 mentation sacrificed so many evenings with unfailing cheerfulness. Thanks are 

 also due to the staff of the laboratory workshops, especially Hr. Allan Boll, who 

 made much of the mechanical structure of the mechanism; and to Fru Gerda 

 Boetius for her fast and accurate typewriting and painstaking proofreading. 



REFERENCES 



1. "Nomenclature for Treating the Motion of a Submerged Body through a 

 Fluid," The Society of Naval Architects and Marine Engineers, Technical 

 and Research Bulletin 1-5, Apr. 1952 



2. Imlay, F.H., "A Nomenclature for Stability and Control," David Taylor 

 Model Basin Report 1319, May 1959 



3. Abkowitz, M.A., "Lectures on Ship Hydrodynamics - Steering and Manoeu- 

 vrability," Hydro- and Aerodynamics Laboratory Report Hy-5, May 1964 



4. Strjz^m-Tejsen, J., "A Digital Computer Technique for Prediction of Stand- 

 ard Maneuvers of Surface Ships," David Taylor Model Basin Report 2130, 

 1966 



380 



