FLOATING. 



383 



But for the very reason that the nature of booms depends 

 on local conditions, no constructions are more varied, and 

 hardly any two booms are alike. In the following paragraphs, 



. L'54. Wooden grating to serve as a In mm. 



therefore, some characteristic forms of booms only will be 

 considered. 



(a) Mode of construction. There are three essential points 



Fig. 255. Transverse section of above. 



in the construction of a boom : the supports, the horizontal 

 bars which stop the sweeps of timber, and the grating of rails 

 that surmounts the boom. 



