SHIP MOTIONS 



205 



Fig. 50 Average of one-tenth highest roll amplitudes of three 



destroyers (designated P, Q, R) (from Warnsinck and St. Denis, 



1957 NSMB Symposium) 



Fig. 51 Average of one-tenth highest pitch amplitudes of three 



destroyers in the rough sea (from Warnsinck and St. Denis, 1957 



NSMB Symposium) 



(1940), Langmaaek (1-1941), and Mockcl (1941, 1944, 

 1953). Ob.servations have been made on many ships 

 when opportunities presented themselves, but there has 

 been no pennauently installed instrumentation. Wave 

 observations have been made visually with the help of a 

 stop watch. Anemometers have been used to deter- 

 mine wind velocities. It has also been found that wind 

 appraisals by ship officers have been very accurate. 

 Great ingenuity has been displayed in designing simple, 

 portable instruments for recording maxima of roll and 

 other data. 



Results of other e.xtensive statistical observations have 

 been published by the personnel of the David Taylor 

 Model Basin. A number of publications is listed in the 

 Bibliography at the end of this chapter under the names 

 of Jasper and Greenspon with several other co-authors. 

 A comprehensi\-e summary of the statistical results was 

 published by Jasper (19.36). 



Jasper (195G) ga^•e a general introduction to the sub- 

 ject of statistics and cited several references for the stat- 

 istical theory. He described three forms of statistical 

 analysis of observed data : 



1 A normal distribution curve, such as shown in 

 Fig. 13. 



2 A Ravleigh ilistribution curve, such as shown in 

 Fig. 14. 



3 A log-normal distribution curve; i.e., the normal 

 distribution of the logarithm of a variable. 



The first two forms are used for analyses of data ob- 

 tained under constant environmental conditions; i.e., 

 for data of one observational run. The last is used for 

 the study of data obtained under different conditions 

 over a long period. 



Jasper (195(3) plotted numerous curves of data on 

 pitching, rolling, and bending stresses obtained from 

 obser\'ations on se\'en ships over an extended period. 

 The distributions of ocean wave heights were based on 

 visual observations taken from records of the U. S. 

 Weather Bureau and also on Darbyshire's (1-1955) meas- 

 urementis. In the summary he stated : 



"The analysis of the voluminous data accumulated 

 during the past several years has indicated that the pitch, 

 roll and heave motions of ships as well as the hull girder 



