Transportation on Water 



347 



and buoyancy, together with all necessary strength. In the 

 submarine boat ballast and air tanks are employed. The air 

 tanks are subdivided into such 

 small compartments that in- 

 jury to one or several does not 

 render the boat unseaworthy. 

 Lifeboats and rafts have been 

 built which have shown re- 

 markable stability in difficult 

 conditions. A life raft, for 

 instance, has been made with 

 many air compartments, and 

 under test has upheld a load 

 of 5000 pounds placed on one 

 side without tipping danger- 

 ously. The raft has been cut 

 into two parts and each part - 

 has carried safely a full load ; 

 of passengers. 



The problem is especially 

 interesting in connection with 

 the sailboat (Fig. 119). A 

 sailboat (Fig. 120) must have enough stability to resist the 

 heeling force of the wind upon the sail. Ballast or a keel 

 weighted with iron or lead are among the means employed to 



make such a boat stable. 

 The mast of a sailboat acts 

 like a lever when the wind 

 tips the boat. The longer 

 the force arm of the lever 

 (pages 254-5), the less the 

 force of the wind required to 

 tip the boat. But as the boat 





FIG. 119. The sailboat. 



FIG. 120. Stability of a sailboat. 

 M = the center of mass ; B = the center 

 of buoyancy. 



heels over, the wind spills 

 over the top of the sail and 



