228 HARBOUR CONSTRUCTION. 



Another kind of wave-screen, somewhat resembling a huge 

 gridiron, was proposed by Mr. M. Scott. 



In this a rubble mound, rising to within about 15 feet of 

 low water, similar to that adopted in ordinary mound break- 

 waters, was to have formed the base ; and upon it it was proposed 

 to build a face wall, up to or slightly above the level of low 

 water, having counter-forts of masonry, about 20 feet apart, 

 extending back upon the mound for a length of from 80 to 120 

 feet. The upper surface of these counter-forts was to have had 

 a slope of 2 or 2J to 1 from their junction with the face wall, 

 and it was intended they should rise to a height of 50 feet above 

 low water. 



Upon their sloping faces, and spanning the distance between 

 them, iron girders were to have been fixed, with spaces of about 

 18 inches between their flanges, thus forming a screen or grating. 



It was claimed, in support of this form of screen, that as 

 waves ran up it the water would drop through the spaces be- 

 tween the girders, and that a similar action would go on as the 

 wave receded, if any of it should remain. This falling water, it 

 was believed, would destroy any undulations which might be 

 passing through the lower parts of the screen. It is not, how- 

 ever, quite clear that the waves would run up the grating in the 

 manner contemplated. It seems more probable that they would 

 be tripped up by the low face wall, and fall with great force 

 upon the girders, which, in view of the power of such breaking 

 waves, would require to be made exceptionally strong to with- 

 stand such repeated shocks. 



In considering this design, it would appear that, in order to 

 give the counter-forts sufficient stability, it would be necessary 

 to employ quite as much material as would be required to con- 

 struct a substantial solid masonry superstructure. The necessity 

 for, or advantage of, the girderwork grating is not, therefore, very 

 apparent. 



Another form of wave-screen, as proposed by Mr. E. K. Calver, 

 R.N., is shown in Fig. 59. 



For a screen suited to a depth of 36 feet at low water, a tidal 

 range of 15 feet, and a wave 15 feet in height, it was proposed 

 that the piles should be 20 inches diameter, and be made of 

 wrought-iron plates at least one inch in thickness. These were 

 to be screwed into the bed of the sea for a depth of 10 feet, 

 and where, from the nature of the bed, this was not practicable, 



