SLIPWAYS. 329 



way. The following rule, constructed from actual observation, 

 is fairly accurate for ways of an inclination of 1 in 20 : 



8 being the total pressure on the returning ram. For other 

 inclinations, some allowance must be made on one side or the 

 other ; but, as the friction due to the weight of vessel and cradle 

 and of the hauling-gear does not vary with change in gradient, 

 the total pull is not as a rule subject to great alterations for a 

 given size of vessel. It also depends as much on the efficiency 

 of the ways as on the inclination. 



At Carthagena, 1 the slips designed by Mr. G. B. Rennie for 

 receiving the ships after being raised by the floating dock were 

 made perfectly level, and the amount of power required to haul 

 the vessels on shore was calculated on the assumption that the 

 launchways for a heavy ship were made with an inclination of 

 J inch to the foot, or 1 in 24, so that about ^ of the weight of 

 the vessel had to be overcome by the hydraulic machinery. 



Resistance on Sliding Slipways. 2 It has been found from 

 experience that a ship can be conveniently launched at an 

 inclination of 1 in 13*3, provided that no immediate contact 

 takes place between the surfaces of the wood, but that they are 

 separated by a thin layer of grease ; for, however carefully pre- 

 pared the surfaces may be, the adhesion is always greater than 

 the downward strain, unless diminished by the use of tallow. 



As the friction during downward and upward movement is 

 the same for like surfaces, it follows that the frictional resistance 

 to be overcome equals 7*5 per cent, of the total weight on an 

 inclination of 1 in 13'3. 



It has also been found by experiment that an additional 

 allowance of 5 per cent, must be made for increase of friction 

 due to rest. 



Further, in hauling up on an incline of 1 in 13 '3, 7*5 per 

 cent, of the dead weight has to be lifted, therefore the power to 

 be provided must equal 20 per cent., or of the united weight 

 of stage and ship. 



Broadside Slipways. 3 The slipways at the shipbuilding yard 

 of the Imperial and Royal Danube Steam Navigation Company 



1 M.PJ.C.R, vol. xxv. p. 333. 2 Ibid., vol. xlviii p. 200. 



Ibid., vol. Ixxix. p. 305. 



