RESISTANCE OF SHIPS 

 Again, the ratio of the wave-making resistances is given by 



i 



while the ratio of eddy resistances 



399 



< 3 > 



Putting (~ ) = D, each of these resistances, and therefore the total 



\ ' ' 

 becomes proportional to D 3 , so that, to quote Mr. Froude, " If a ship be 



35 



r 



3-0 



Model ir> knots 



"W 



I 



3000 



tooo 



7000 



6000 



SOOO* 



woo i 



18 19 20 



/.' ,'? 13 14 15 16 17 

 Corresponding Speed or Snips m 



FIG. 183. 



D times the dimensions of the model, and if at speeds FI, V%, F 3 , the 

 measured resistances of the model are RI, E 2 , R 3 , then for speeds 

 Fi \TB, F 2 \/"D; F 3 V~D~, the resistances of the ship will be I) 3 # lf 

 D 3 RZ, D 3 R 3 . To the speeds of the model and ship thus related it is 

 convenient to apply the term ' corresponding speeds.' " 



In determining the resistance of any proposed ship, a scale model is 

 made usually of paraffin wax, and is towed through still water, the 

 resistance corresponding to any speed being noted. Thus in Fig. 183, 

 A A represents a resistance curve, the vertical ordinates from the line X 

 representing to scale the total resistance of the model. 



The area and length of the wetted surface being known, and the 



