6o FLOATING DRY DOCKS IN THE UNITED STATES. 



paper will also be found in the Transactions of the American Society of 

 Civil Engineers for 1907. 



In 1906 the author was retained by a large dry docking and ship repair 

 company to prepare plans for a floating dry dock. The general require- 

 ments were that the dock should ultimately have a lifting capacity of 

 20,000 tons and that approximately 12,000 tons lifting power was to be 

 built at the beginning and added to later on. 



While the author's experience had previously dealt with wood as a 

 structural material for floating dry docks, he was also familiar with steel 

 for such structures, and owing to the fact that all docks of approximately 

 this size had been built of steel, attention was directed to that material, 

 and a careful study made resulted in the selection and design of the Rennie 

 type of dock with steel pontoons and wings (Plate 15), the pontoons being 

 14 feet deep, 28 feet long and 127 feet wide. 



By reference to Plates 16, 17, 18 and 19, the general construction of these 

 pontoons will be clearly understood. The steel wings were to be 40 feet 

 high to give ample longitudinal rigidity. The details of this dock were 

 very carefully worked out so that accurate weights were arrived at. They 

 were 6,600 tons for the pontoons and 2,700 tons for the wings, or a total 

 of 10,300 tons for the structure, which, on a basis of 20,000 tons lifting 

 power, gives as a factor of structural weight relative to lifting power, of 

 5 : 10, which agrees fairly well with other large docks previously designed 

 and built. 



The fact that a working stress of 12,000 pounds per square inch was 

 used throughout and that the wings of the Rennie type of dock were made 

 of exceptional depth to insure longitudinal rigidity, will account for a 

 somewhat higher weight factor. 



While this dock was not built, bids which were received indicated that 

 the cost of the dock completed would be approximately $57 per ton of 

 lifting power. For a more complete description of this dock and the novel 

 method of pumping by compressed air which it was intended to use, those 

 interested are referred to a paper entitled "A New Method of Pumping 

 Floating Dry Docks," read before the Brooklyn Engineers' Club on May 

 9, 1907. The reason for introducing the matter here is to effect a com- 

 parison between this structure and similar docks with wooden pontoons. 



Referring to Plate 20, there will be seen a pontoon dock of 7,000 tons 

 lifting capacity, with steel wings and wooden pontoons. The detailed 

 construction of the wooden pontoons is shown in Plate 2 1 . These pontoons 

 are 100 feet long, 1 1 feet deep and 32 feet wide. Each pontoon has eleven 

 frames or trusses on 3 -foot centers. Top and bottom planking is 4-inch, 



