CHAPTER XIII. 



\VAVfsCREENS AND FLOATING BREAKWATERS. 



Designs for wave-screens and floating breakwaters based upon wrong hypotheses 

 Description of wave-screens proposed by Hays, Scott, and Calver Floating 

 breakwaters Examples of, in nature Icebergs Weed-fields Size of effective 

 floating breakwater Behaviour of vessels riding at anchor Impossibility of 

 mooring floating breakwaters Inefficiency of floating breakwaters Booms at 

 harbour mouths Floating- weed type of breakwater The mooring of lightships. 



VARIOUS proposals have from time to time been made for inter- 

 cepting and breaking up waves by means of screens and floating 

 breakwaters. In such designs the prominent idea seems to have 

 been that waves could be stopped or broken up and destroyed 

 without the structures by which this was brought about having 

 to sustain the shock of the wave-impact ; in other words, that 

 action and reaction are not equal. 



There can, however, be little doubt that the strain upon any 

 structure employed in the reduction of waves, by whatever 

 means it may be brought about, will be in exact proportion to 

 the amount of reduction effected in a given time. 



In the year 1858, 1 Mr. W. B. Hays gave evidence before a 

 Select Committee on Harbours of Refuge, respecting a wave- 

 screen which he had designed, and which he claimed was adapted 

 for harbours of refuge in deep water. Fig. 58, p. 226, which is 

 copied from a drawing illustrating the committee's report, 2 repre- 

 sents the structure referred to, as adapted to a depth of 3(j feet 

 at low water, and a tidal range of 10 feet. 



The advantages of this system were stated to be (a) its small 

 cost ; (6) the facility and rapidity with which it could be erected ; 

 and (c) that, in consequence of the inconsiderable depth of the 



1 A description of Mr. Hays's system was also published, in pamphlet form, in 

 the year 1856, reprinted from the Civil Engineers' and Architects' Journal. 



2 " Report of Select Committee on Harbours of Refuge, 1858." 



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