388 



WOOD TRANSPORT BY WATER, 



Water-sawmills always require booms to keep out the float- 

 ing wood which is intended to pass beyond them. Such booms 



Fig. 261. Trestle for a boom. 



must be constructed so that part of the grating may be readily 

 removable and allow entrance for the butts which are to be 



Fig. 262. Trestle boom. 



sawn. The grating is, therefore, frequently provided with 

 the arrangement shown in Fig. 259. The hooks at n n are 

 for the removal of the rails, each of which is perforated for 



