44 IMPROVED FISHERY HARBOUR ACCOMMODATION 



shall not be at a loss to apply them to the projection of an 

 artificial harbour. 



REDUCTIVE POWER IN HARBOURS. 



In designing a harbour the engineer will, as a matter of 

 course, endeavour to make his work as perfect in shelter 

 and tranquillity as possible, to which end the waves should 

 be reduced in height with all speed after passing the seaward 

 extremity of the work. This feature may be looked on as 

 the chief requirement in harbour design, and the faculty 

 which any particular harbour possesses in this respect is 

 termed its reductive power. 



The reduction of the waves when they are deflected from 

 their original direction, and made to diverge into sheltered 

 water, is particularly adverted to by Mr. Thomas Stevenson, 

 p. 1 1 8, 'Design and Construction of Harbours,' and he 

 observes : " When a wave encounters an obstacle such as a 

 breakwater, if we suppose the portion which strikes it to be 

 annihilated by the impact, or to be reflected seawards, the 

 portion which is neither destroyed nor interrupted will 

 pass onwards, and a part will spread laterally behind the 

 breakwater." 



Again, at p. 119, he says : " When the waves are deflected 

 by a pier with a free end, and run along its inner side, 

 the reduction which they suffer will be due to the distance 

 passed over, and to the angle of deviation produced by the 

 pier." 



At p. 1 20, also : "The ultimate object of every harbour is 

 to preserve the tranquillity of the inclosed area by lowering 

 the height of the waves as they enter, and this property is 

 variously possessed by harbours of different forms, and 

 depends on the relative widths of the entrance and the 



