An Assessment of a Non-mechanical Means of Towing a Hydrodynamic Scale Model of a Planing Hull in a Seastate for the Measurement of Vertical Acceleration

An understanding of expected rigid body impact accelerations of planing hulls operating in an anticipated seaway is critical to the proper design of these craft. Since at least the late 1960's preliminary prediction methods, developed from model scale data have been successfully utilized by designers. These methods have ranged from semi-empirical equations and design charts combined with statistical distribution fits to more modern numerical and computational methods. As these tools are all based on data recorded during extreme impact accelerations there is frequently extraneous data that corrupts the data of interest. For model tests this is attributed largely to mechanically induced vibrations from the towing carriage. A method of eliminating the mechanical connection of the model to the carriage and towing the model with a string bridle was tested and the resultant model heave, pitch, and vertical acceleration data was compared for the same model towed with a standard mechanical carriage. Results and analysis in the time and frequency domain along with a comparison of the statistical results are presented. Suggestions for reducing extraneous signal inputs are suggested for model scale testing.