DOUBLE-POWER DOCK. 



303 



Double-power Dock. 1 For the double-power dock designed by 

 Messrs. Standfield and Clark, two special features are claimed. 

 The first is that of utilizing the buoyancy of its sides as well as 





that of the bottom, by which a much less quantity of material 

 is required for doing the same work as an ordinary floating 

 dock. 



The second feature is that it is able to dock itself, so that 

 every part can be ex- 

 amined, cleaned, and 

 painted, the life of the 

 dock being thus consider- 

 ably prolonged. 



In an ordinary float- 

 ing dock the sides add to 

 the weight to be lifted, 

 and, as far as the power 

 of the dock is concerned, 

 they represent useless 

 cost. All the work has to 

 be done by the bottom or pontoon, which must therefore possess 

 sufficient buoyancy to lift the two sides of the dock as well as 

 the vessel. If, therefore, arrangements be made to avoid the 

 necessity of lifting the weight of the two sides, a great economy 

 is effected either by using a smaller pontoon or lifting a heavier 

 vessel for any given weight of material in the dock. Moreover, 

 if means be taken for making the buoyancy of the two sides 

 assist the pontoon, a still greater economy will be effected in 

 either of these directions. 



It is claimed that this economy has been effected in the 



1 Trans, Society of Engineers, 1881, p. 90 ; Engineering, 1886, p. 396. 



FIG. 299. 



