232 HARBOUR CONSTRUCTION. 



vessel, riding head to wind, is comparatively steady, because 

 she spans, it may be, the whole or the greater part of the 

 distance between two waves, and the several motions of the 

 Wave-particles, acting upon her hull, neutralize each other. A 

 smaller vessel, on the other hand, whose length, let us suppose, 

 does not exceed one-third that of a wave, is seen to range back- 

 wards and forwards, and up and down, as each wave passes. 

 Such a vessel, when in the trough of the sea, is to some extent 

 sheltered from the wind, and she advances with the water- 

 particles towards each on-coming wave (see Fig. 6, p. 25). At 

 such times her cable, being to a considerable extent relieved of 

 strain, sags and becomes slack. When, however, the vessel is 

 riding on the top of a wave, not only is the motion of the 

 water-particles reversed, but she is exposed to the full force of 

 the wind, and, with her bows high in the air, she is hurled back 

 with tremendous violence, her moorings at such times being 

 often tried to the uttermost. The vessel thus advances and is 

 driven back, and rises and falls in obedience to the motion of 

 the water-particles, but the waves themselves are not reduced 

 or altered in any way. 



From the foregoing, it may, I think, be gathered that a 

 floating structure it would not be correct to call it a break- 

 water of indefinite length, but having a width of, say, 100 to 

 150 feet, exposed to waves of 400 or 500 feet in length, i.e. 

 crest to crest, would behave in much the same way as the 

 smaller vessel we have been considering ; but, inasmuch as the 

 fine stem and bows of the vessel would be represented by 

 the bluff face of the structure, I leave the reader to imagine 

 what kind of moorings would be required to hold it. 



The idea of a floating breakwater with a width sufficient to 

 span from crest to crest of even two long storm-waves is absurd, 

 and need not, therefore, be considered. 



There can be no doubt that a floating structure, capable of 

 acting as a breakwater in a heavy sea, must be of such gigantic 

 proportions as to render its construction, as well as its mooring, 

 practically impossible. Small surface waves might be stopped 

 by a correspondingly smaller structure, but these would probably 

 be unobjectionable if allowed to pass. 



A boat alongside and under the lee of a large ship riding 

 broadside on to the waves derives shelter from surface Upper ; 

 but, in even a moderate sea, it ranges up and down against the 



