FLOATING DRY DOCKS IN THE UNITED STATES. 65 



capacity, there does not seem to be any engineering limit to the size to 

 which the Rennie type of dock can be built with wooden pontoons. A 

 carefully worked-out pontoon for a 20,000-ton dock shows dimensions of 

 i3o'X44'X 15' and it will be readily understood that this structure is well 

 within the practical limits for timber work. 



Regarding the cost of tlie different types of floating dry docks, it is, 

 of course, not possible to make any definite statements, as they are much 

 influenced by the varying cost of material and the location where the dock 

 is to be constructed. For the relative cost of the different types of docks 

 on the eastern coast of the United States, the following figures may be 

 taken as being approximately correct:— 



COST PER TON OP LIFTING POWER. 



Balance sectional timber dock with centrifugal pumps $32 per ton. 



All wood pontoon dock with continuous wings 35 per ton. 



Pontoon dock, steel wings and wooden pontoons .... 42 per ton. 



All steel pontoon dock 57 per ton. 



Government steel dock, Dewey type 62 per ton. 



The comparative cost for the western coast of the United States will 

 be quite different on account of the increased cost of steel and the much 

 lower cost of timber. 



APPENDIX. 



Through the kindness of the President, Mr. Stevenson Taylor, and by 

 permission of Mr. James W. Folger, I am enabled to add to my paper the 

 following which is of historic interest in relation to floating dry docks. 



Referring to the accompanying picture, Plate 14, there will be seen one 

 of the first floating dry docks, or, as it was then called a "Camel," which 

 was built in the United States. The view shows Brant Point, Harbor of 

 Nantucket, about 1842, when this "Camel" was built. It was used for en- 

 tering vessels over the shoals in Nantucket Harbor until about 1850. 



Additional information has been furnished by Mr. A. Milne, of Nan- 

 tucket, Mass., as follows : 



"The 'Camels' were each 135 feet long, had a depth of about 19 feet, 

 a width of 29 feet on the bottom and 20 feet on deck, drew 10 feet 2 inches 

 on a level and were connected by fifteen chains, five of i| inches and ten of 

 if inches which bore 800 tons weight. It required 200 tons to sink the 'Camels' 



