94 Ocean Waves 



water be changed, the force of buoyancy to rectify the 

 position of the larger body will be ten times as great as that 

 exerted on the less, but it has, of course, ten times the mass 

 to move, and in the latter case, the force partially opposes 

 itself, as illustrated in the figure, (fig. ^ ) paragraph 22. 



30. But the motion of a floating body, however large, 

 being simply due to the resultant of all the forces acting 

 upon it, the actual motion of such body in space, is a 

 measure of the mechanical effect exerted on it. Thus, if a 

 vessel of 1,200 tons, by the action of wave forces, be raised 

 or heaved two feet in a second ; the mechanical effect is 

 equivalent to a weight of 1,200 tons raised two feet per 

 second, or 14*4,000 tons raised one foot per minute, which is 

 nearly equal to 10,000 horse power. Such, for instance, 

 would represent the gigantic impetus or force of the blow 

 with which a vessel so circumstanced would be dashed 

 against a rock. 



In regard to the angular motion, the prodigious effort of 

 the force of buoyancy acting upon a surface of the eighth or 

 even the fourth of an acre, is on the same stupendous scale. 



It follows from the preceding considerations that every 

 portion of a body floating upon waves tends to move in the 

 same orbit as the particles of water which would occupy 

 its place were there no floating body. The rigidit}'- of the 

 ship unites or opposes these tendencies, and the whole mass 

 moves only in accordance with their resultant ; the stability 

 of the vessel depending on the degree with which these 

 tendencies are counteracted by her magnitude and build. 

 But it hence follows that the straining of a vessel in a sea- 

 way increases in ^^'^'o-portion with the increase in her 

 stability. I think this somewhat important distinction 

 should not be forgotten in the general eagerness to produce 

 stable ships. The greater the freedom with which a vessel 

 rides on the waves, the less will she be strained by the 

 action of their forces. Nothing can be more certain than 

 that if a vessel does not heel on a wave, the wave must 

 strike her ; and no vessel is so strong as to withstand, with- 

 out detriment, for a lengthened period the continuous and 

 unwearying assault of those gigantic forces by which she is 

 surrounded. If a vessel is too unstable, she is liable to 

 overset ; but if her stability be increased to an undue 

 amount she may be unsafe from another cause, namely, 

 excessive straining, possibly eventuating after a long time 

 in unlooked-for leakage or fracture. Between these two 



