ABSTRACT 



The results of pitch and heave amplitude measurements are presented 

 for five different models which were tested in regular waves representing head 

 seas conditions. The data are given in the form of curves, at constant Froude 

 numbers, of nondimensional motion parameters plotted against the ratio of the 

 natural period to the period of encounter (tuning factor). It is shown that the 

 motion results can be related, through empirical curves, to certain basic hull 

 parameters which are developed and discussed in the report.. Thus, the experi- 

 mental data can be used to predict the motion amplitudes of various hull forms 

 which have characteristics similar to those of the five models used in this 

 investigation. 



INTRODUCTION 



The pitch and heave amplitude data, which form the basis of this report, were obtained 

 in connection with largely unrelated model studies performed at David Taylor Model Basin 

 over the past two years. ^'■^ The results of these studies have already been presented in 

 individual reports, but are given here anew in order to permit a comparison of the pitch and 

 heave characteristics among the various hull forms. 



The first part of this paper is concerned with a description of the various models and 

 test facilities used to obtain motion amplitudes for head seas test conditions. Next, the meth- 

 ods of data analysis used in the present investigation are described. Finally, some hull 

 parameters which may have a predominant influence on motion characteristics are suggested 

 and discussed. 



MODEL TESTS 



A list of particulars for five models representing five different hull forms is given in 

 Table 1. All of the models are approximately 20 ft in length. They were tested in the TMB 

 1800-ft basin, which is equipped with a pneumatic wavemaker for generating regular head or 

 following seas.^ The models were self-propelled under a carriage which spans the 51-ft 

 basin width. The carriage was used to guide the models on a straight course and to carry 

 test equipment and personnel. Pivoted struts and brackets permit freedom in pitch, heave, and 

 surge, but restrain the model in roll, yaw, and sway. Pitch angles were measured using a 

 Minneapolis-Honeywell vertical gyro. Heave am.plitudes were obtained from vertical acceler- 

 ation measurements, as well as from a linear potentiometer between the model and a fixed 

 reference on the carriage. 



References are listed on page 18. 



