SAILING CRAFT 87 



enough against their other tendency to draw 

 apart. 



All means that strengthen a well-built hull 

 longitudinally have also been made to add their 

 quota to its transverse strength. The ribs 

 spring from the solid mass of their own floors 

 bolted in between the keelson and the keel; 

 and the planking, or skin, is let into the 

 rabbets, or side grooves, of the keel and firmly 

 fastened to the ribs throughout by hardwood 

 pegs called treenails. The decks are, in them- 

 selves, a source of weakness. The beams sup- 

 porting them are like the rafters of a house, 

 which, of course, work the walls apart under 

 pressure from the floors — and here, as in every 

 other detail, the stability required for a house 

 is nothing to what is required for a ship. The 

 way to overcome this difficulty is to make the 

 decks and beams so many bridges holding the 

 sides together. At the point of junction of every 

 beam-end with a shelf -piece, waterway, and rib 

 there is an arrangement of bolts and dowell- 

 ings (or dovetailings) which makes the whole 

 as solid as possible. An extra bolt through 

 the waterway, rib, and outside planking adds 

 to the strength ; and a knee, or angular piece 

 of wood or iron connecting the shelf with the 

 under side of the beam, almost completes the 



