2 Wilson and Weston, Torpedo-Boat Destroyers. 



It is, therefore, to these effects that the authors would 

 draw attention, since it appears to them that in the case 

 of a vessel unsuitably designed, the stresses might be 

 largely augmented, even so far as to severely strain, if 

 not actually rupture, the vessel. At the same time a 

 further element of danger is introduced, owing to the con- 

 stant reversal and repetition of such stress, which is going 

 on during the motion. This reversal and repetition, which 

 in a highly strained material might not be of primary 

 importance if the material were uniform in structure, may 

 become a serious factor in the case of any arrangement of 

 rivetted plates and beams. 



When a vessel of this class is at rest on a sea, the 

 surface of which is covered with waves approaching the 

 vessel in a regular manner, the motion would be one of 

 combined pitching and tossing, depending on the relation 

 between the length of the waves and that of the boat. If 

 the length of the waves is short, compared with the length 

 of the vessel, the vertical motion and the pitching motion 

 will be inappreciably small. If, however, the wave-length 

 is nearly equal to the length of the vessel, the vertical 

 motion and the pitching motion will be considerable. 

 If, in addition, the boat is moving at a definite rate across 

 waves of this nature, the inertia of the vessel would tend 

 to diminish the pitching motion ; for the interval of time 

 during which the disturbing couple would act decreases 

 as the speed of the vessel, relatively to the waves, 

 increases. The authors are led to believe that this fact is 

 also substantiated by actual experience with this class of 

 vessel. 



At the outset of the following investigation, it was 

 thought advisable to take into consideration the disturb- 

 ing forces caused by the pitching motion, but, on forming 

 the equations of motion for the boat considered as a 



