582 



INDUSTRIAL USES OF WOOD. 



pieces are 30 to 40 feet long. Curved woods are required 

 chiefly which have a sagitta or camber of 2'5 and T5 centi- 

 meters per meter (i.e. ^ and ^ a ), but this may be exceeded 

 in certain pieces as in Fig. 332. The beams used for sup- 

 porting the deck are much less curved. 



Wood is now bent artificially for shipbuilding, as in certain 

 factories in Hungary, but probably it is then weaker than 

 naturally curved wood. 



Kneed timber is formed where a bough parts from the 

 parent stem as in Fig. 333. The branch should accord in its 

 dimensions with the stem, and not be 

 too small when compared with the 

 latter. 



The chief use of knee-pieces is in 

 the construction of river-barges ; wood 

 of smaller size is then required than 

 for shipbuilding, and in that case the 

 arm a, Fig. 333, is much longer than 

 l>, whilst for ships it is onty twice as 

 long. In North Germany, where oak 

 is scarce, large, branchy Scots-pines 

 are used for knees, which otherwise 

 would be fit only for firewood. Such 

 knees last 10 years in barges. Beech- 

 wood also may be so used in the interior of vessels. In Saxony 

 use is made of the lower part of a spruce stem with a strong 

 root attached ; this may be 15 to 20 feet long, and 7 to 10 

 inches thick. 



It is difficult to give the proper dimensions for compass- 

 timber used in shipbuilding, but the longer and thicker, the 

 more valuable they are ; no sapwood is included ; 10 inches 

 diameter, and 15 to 20 feet length, represent the minimum 

 dimensions. When used for barges and boats the diameter 

 of knee-pieces may go down to 4 inches. 



Long, straight pieces of timber are used for keels, but are 

 sawn chiefly into planks for the inner, or outer, casing of 

 vessels, and even larger sizes are required than for com- 

 pass-timber : lengths below 24 to 30 feet, and a diameter 

 of less than a foot at the smaller end, are not permissible. 



Fig. 333. Knee-piece. 



