VARIOUS TYPES OF BREAKWATERS. 



213 



pell-mell; and the system is open to the objection, already 

 pointed out, that the lower blocks derive but little help from the 

 weight of those above them. When, however, very heavy blocks 

 are employed, this objection in a measure disappears. 



FIG. 53. 



FIG. 52. Mound breakwater faced and capped with stepped block-work. Type (0). 



Notching the blocks in the manner shown in the above 

 sketch (Fig. 52), or slightly inclining them backwards (Fig. 

 53), as was done in the breakwater at Cagliari, in Italy, in- 

 creases their stability, while 

 adding but little, if anything, 

 to their cost. 



Breakwaters constructed 

 on this principle in the Medi- 

 terranean, in positions where 

 they are sometimes subjected 

 to the impact of waves as high as 21 feet, appear, so far, to have 

 stood well, they having cost but little in maintenance. 



They are easily constructed by means of pontoons fitted with 

 derricks, the speed with which the work is carried on being 

 thus largely a question of the amount of plant employed. 



Breakwaters of this type are comparatively free from sea- 

 risk whilst in progress. 



All the blocks are bedded " dry," no mortar being used. 



The weight of the blocks employed by the Italian engineers 

 in constructing the breakwaters to which I have referred, varied 

 from about 28 tons to 36 tons each. 



