WAVE-SCREENS AND FLOATING BREAKWATERS. 231 



satisfied that any attempt to arrest heavy seas by mechanical 

 means must ultimately fail. 



Apart from the force of the wind and waves, the probability 

 of floating wreckage or of unmanageable vessels drifting down 

 upon a wave-screen during a gale should not be lost sight of. 

 This risk equally applies to floating breakwaters (so called) 

 which we will now pass on to consider. 



Floating Breakwaters. If we look to nature for types of 

 breakwaters, we find the mound type exemplified by boulder 

 beaches, the vertical type by sea cliffs, wave-breakers or pell- 

 mell work by huge boulders at the bases of cliffs, and floating 

 breakwaters by gigantic icebergs and large areas of floating 

 seaweed. 



Engineers have been able, with more or less success, to copy 

 the examples which nature thus presents, with the exception 

 of the two last-named. 



Icebergs and weed-fields, whenever they possess the attri- 

 butes of breakwaters, are found to be of such gigantic propor- 

 tions as to render imitation on a sufficiently large scale hopeless. 

 Icebergs are, moreover, wanderers; and he would be a bold 

 man indeed who would attempt to moor one. 



A large iceberg is capable of acting as a breakwater because 

 of the extensive area which it covers, and the great depth below 

 the water surface to which it extends. 



Its area being sufficient to cover several waves, it floats at 

 the normal water-level. This it does in the heaviest seas, which, 

 great as they may be, are small in comparison to its mass, 

 Hence, as it does not accommodate itself to the motion or lift 

 of the waves, they are either reflected from it, or dash themselves 

 against it and are destroyed. 



Large vessels, drawing, it may be, 25 to 28 feet of water, 

 when running on a course parallel to the waves, rise and fall to 

 them as they pass, thus allowing them to go on their way 

 unchecked and unaltered. 



In order that a vessel should not thus accommodate itself to 

 storm- waves, when broadside on to them, it would be necessary 

 for it to possess sufficient beam (say 1500 or 2000 feet, or even 

 more) to cover at least three such wave-crests. 



Any one who has watched the behaviour of vessels riding at 

 anchor in a heavy sea cannot fail to have noticad how greatly 

 the movements of the larger and smaller ones differ. A long 



