the five models, at the same Froude number F =0.20 and tuning factor A = T^/T^ = 1.0. Speeds 

 vary from about 13 to 19 knots, wave-length/ship-length ratios vary from about 0.91 to 1.20, 

 and wave lengths vary from about 450 to 750 ft. 



As an example of the use of the experimental results for motion predictions, consider 

 the following hull particulars of a typical small aircraft carrier. 



^(ft) 



L/B 



L/H 



D/H 



C. 



C 



V 



486 



7.54 



24.5 



3.25 



0.747 



0.765 



The mean beam-draft ratio of the ship, C^B/C^H = 3.17, is almost identical with that of 

 Model 4. For the same Froude numbers and tuning factors, therefore, the predicted heave 

 parameters will be approximately equal to those measured for Model 4. The pitch parameters, 

 on the other hand, will have values that are approximately midway between those measured 

 for Model 2 and Model 3, since L/V^^^ = 6.86 for the aircraft carrier is about midway between 

 corresponding values for the two models. 



Given values of Froude number and tuning factor can be easily converted to correspond- 

 ing values of speed and wave length using the relations 



F = 



V 

 7L 



A = 



and T. = 



^/g \/2n + V 



In dimensionless form, the period of encounter is given by 



i{ 



X/L 



\lk/'2TTL + F 



Brief mention should be made of two additional applications of the empirical curves 

 presented in this report. One is their use for the prediction of energy spectra for pitch and 

 heave of the prototype. Following the methods given in Reference 13, among others, the 

 empirical data can be used to estimate the so-called "amplitude response operators" to be 

 used for the calculation of the energy spectra of a ship in any given sea state. The second 

 application is the use of a family of empirical curves, such as that given in Figure 11, to 

 characterize the motion results obtained in a particular test facility. A correlation study of 

 various towing tanks can then be based on tests of many models which are similar but not 

 necessarily the same for all tanks. Such a correlation study can be expected to produce 

 information of much greater value than a study based on a single model tested in all the tanks. 



17 



