Messrs. "'J. Larras and H. Colin in their article of December 194-7 

 published in the periodical Travaux. 



The following data are obtained from page 609 of that 

 compilation showing the corresponding slopes, depths, and weights 

 of blocks or stones. 



life te rials 



Minimum weight, 

 metric tons 



Maximum 

 slope 



Minimum 

 Depth, meters 



Artificial blocks 

 Natural stones 



same 

 Quarry waste 



50 



4 

 1 



5/4 



3/2 

 3/2 

 2/1 



-5 

 -11 

 -14 

 -18 



There can also be adopted, as a stable upper surface slope, 

 that of 3A formed by 50- ton concrete blocks, adopted for strengthen- 

 ing the North dike which, according to the cited article, has 

 withstood perfectly even the worst storm (3 February 1934) ever 

 suffered by the port of Argel and which destroyed a large part of 

 the Mustafa dike. Likewise, we can adopt the toe depth of 35 

 meters, which this North dike reaches. 



The maximum characteristics of waves from that very violent 

 storm are known with an approximation acceptable for practical 

 purposes, and will be used in comparisons which follow, The wave 

 period reached 13 3/4 seconds.-!:- The maximum amplitude of a 

 beacon buoy** in the exterior of the port was 7 meters, and this 

 constitutes an approximate upper limit to the wave height. 



To explain the 9-meter sheets observed passing over the 

 parapets of the dikes, it has been conjectured, simply by inertia, 

 and abstracting other forces such as those of buoyancy, that the 

 amplitude of the vertical movement of the buoy was less than the 

 wave height. 



The buoy and whole float of constant horizontal section can be 

 likened to a vertical oscillator whose own natural period, was un- 

 doubtedly much less than the 13 3/4 seconds of the period of the 

 wave. Under these conditions, the maximum vertical amplitude of 

 the oscillator, or buoy, must be practically equal to or, better, 

 somewhat greater than that of the sea , 



For hypothetical lesser periods of the sea, that might 

 approximate the buoy's own natural period the vertical oscillations 

 of the buoy, amplified by resonance, would be much greater than 



*- See the view presented to the second question (subject) of the 

 second section of the XVI International Congress of Navigation by 

 Messrs. M. Benezit and M. Renaud. 



*# n boya de balizamiento" 



