400 



MOTION SICKNESS, II 



(taking x = when t = 0). The velocity 

 and accelerations are simply obtained by 

 differentiating equation (2) ; in the resulting 

 expressions, putting the trigonometric fac- 

 tor equal to unity gives the maximum veloc- 

 ity and acceleration. If x is an angle (in 

 radians), then at a distance R from the axis 

 of rotation the linear (tangential) displace- 

 ment is obtained by multiplying equations 

 (1) and (2) through by R. This method of 

 computation was used in connection with 

 motion sickness by Sjoberg (34), who con- 

 sidered the motion of a vessel to be the super- 



(for reasons to be discussed below). He 

 concluded that the maximum angular ac- 

 celerations which could be expected would 

 be about 5° per sec, and the maximum 

 linear accelerations about 0.5 g. Morales 

 (23) has made similar computations for 

 several classes of naval vessels, employing 

 sallying data.^ In this study the maximum 

 linear accelerations (obtained on the as- 

 sumption that all components add) were 

 calculated at three positions on the vessel 

 (Table I and Fig. 1); an average of these 

 values for each vessel gives a rough idea of 



Angle of roll 



Angle of pitch 



Scend 



Fig. 1. Schema to illustrate the three important oscillatory motions of a vessel, and the positions 

 at which the accelerations in Table I have been computed. 



position of three oscillations (Fig. 1): 

 rolling, or rotation in the transverse plane; 

 pitching, or rotation in the longitudinal 

 plane; and scending, or vertical translation 

 of the center of mass normal to the hori- 

 zontal plane. The axes of the rotations 

 and of the translation intersect approxi- 

 mately at the center of the vessel near the 

 water line. 



Sjoberg (34) studied the contributions of 

 rolling and pitching in a "passenger vessel 

 of average size," paying special attention 

 to the linear accelerations thus generated 



the upper limit of forces to which personnel 

 may be subjected, and also gives some no- 

 tion of the relative capacity of various classes 

 of vessels for producing these forces. It 

 may be noted parenthetically that the 

 "average" maximum acceleration for the 

 various classes parallels at least roughly 

 the sickness-inducing characteristics of the 

 classes. It is also well to mark for future 

 reference that most of the accelerations lie 



1 Kindly furnished by the Design Stability 

 Section of the Bureau of ships, Navy Department. 



