SHIP- AND BOAT-BUILDING. 129 



whole framework of ships on the Dahnatiau Coast ; the wood of 

 elm, maple, lime, &c., and boxwood are used for models. 



3. Permissible Defects. 



All wood used for shipbuilding cannot be entirely free from 

 defects, for if that were the case, sufficient wood would not be 

 obtainable from a large forest district to make a single ship, as 

 old oakwood is seldom perfectly sound. 



Wood which, owing to its dimensions, is ranked as first-class, 

 may have small local defects which do not practically weaken the 

 balks. Brown spots and rings at the larger end of a balk, pro- 

 vided they do not penetrate far into the wood, and may be 

 removed by shortening the balk, need not cause it to be rejected. 

 Where small patches of red or white rot and other similar defects 

 occur, which are thoroughly dried and are not expected to extend 

 any further, the decision of the admissibility of the affected wood 

 must be left to an expert. 



Large heart-shakes, frost-cracks, twisted fibre, deep-going 

 black and brown marks, rotten places descending from branches, 

 are defects which naturally exclude the timber possessing them 

 from use in shipbuilding. 



Shipbuilders as much as possible avoid using any defective 

 timber in new ships, whilst in repairing old ships such material 

 may be more admissible. 



4. Shape and Dimensions. 



All shipbuilding timber is either wood for construction, or 

 mast- or spar- wood. 



(a) Timber used in Construction. — This comprises curved and 

 long wood. 



Curved or compass timber is chiefly used in the framework 

 of ships. As a rule, the curvature should be uniform throughout 

 the piece (fig. 34), or greatest at one-third from one of its ends, 

 and when this is one-third the distance from its larger end 

 (fig. 35), the piece is most valuable. Some of these pieces are 

 thirty to forty feet long. Curved woods are chiefly required 

 Avhich have a sagitta or camber of 2*5 and 1'5 centimeters per 

 meter {i.e. :jV and o-g-^), but this may be exceeded in certain pieces 



VOL. v. K 



