8 Wilson and Weston, Torpedo-Boat Destroyers. 

 with in great storms in micl-ocean. On substitutiuj^ this 

 value for -^ in equation (2) the maximum dynamical 



stress /= — (2'o8) = iO'4 tons per Q". 



The conclusion drawn from this result is that, if the 

 section of the vessel is strong enough to resist the statical 

 stress, then for all ordinary velocities and depths it is 

 strong enough to resist any increment of stress due to the 

 periodic nature of the motion. However, to ensure that 

 this shall be the case, it is necessary that the workman- 

 ship in the construction of the frame of the vessel should 

 be of the highest possible character, in order that the 

 modulus of elasticity may be as large as possible. 



The autiiors next investigated the vibrations which 

 occur when the vessel crosses the waves in a direction 

 making an angle 9 with a normal to the crest lines. In 

 this case the motion divides itself into a vibration in a 

 vertical plane, through the longitudinal axis of the vessel, 

 and a torsional vibration about that axis. 



It is found that the combined effects of torsional and 

 bending stress are less than in the case previouslj' investi- 

 gated, for the standard dimensions of vessel kindly 

 supplied by Mr. Watt*^, Director of Naval Construction. 



This appears in Appendix II., whilst in Appendix 

 ill. these conclusions are applied to the case of a typical 

 destroyer of the British Navy. 



Appendix I. 

 The equation of the wave surface is 

 h^ h„ + ^sin— (a- -f- vt). 



A 



The axes of coordinates are the centre line of vessel when 



