FI.OATING DRY DOCKS IN THE UNITED STATES. 63 



been made in the upper woodwork, which, of course, will deteriorate equal 

 to, or somewhat more rapidly than, ordinary woodwork of buildings. 



The John N. Robins Co., Erie Basin, Brooklyn, N. Y., has two large 

 floating dry docks other than the pontoon dock with steel wings previously 

 referred to. One of these docks, known as the Balance Dock, was built 

 by William H. Webb and finished in October, 1854 (Plate 25), and has 

 been in continuous use ever since. The writer has recently had the oppor- 

 tunity of thoroughly examining and overhauling this dock and changing 

 over the pumping plant from steam to electric operation. A most thorough 

 examination of the interior and weight-supporting timbers showed practi- 

 cally no deterioration, not a particle of decayed wood being found below 

 the deck. Certain corrections were made, due to faults in the original 

 design, to obtain a more positive control of the dock in operation, and 

 since the overhauling the dock has lifted fully as heavy ships as at any 

 time in its history. Much of the upper woodwork of this dock has been 

 replaced and much more will have to be replaced from time to time. 



Attention should be called to the fact that owing to the size of this 

 structure, 330 feet long by 100 feet wide, it has never been possible to 

 entirely remove it from the water. 



The other large floating dry dock of the John N. Robins Co. is of the 

 Dodge-Burgess type of sectional dock, having ten sections with pontoons 

 100 feet by 30 feet. The general construction of this dock can be seen by 

 referring to Plate 26 and to the work by Stuart entitled "Naval Dry Docks 

 of the United States," previously referred to, where there will be found 

 excellent descriptions with illustrations of similar docks built for the United 

 States Government at Philadelphia and Portsmouth, N. H. 



In protecting the wooden pontoons of floating dry docks and, in fact, 

 all under- water parts of floating dry docks, it has been the universal custom 

 to first thoroughly grave them with brown tar poisoned with arsenic, then 

 apply two layers of best sheatliing felt, thoroughly graving each layer in a 

 similar way, and then over this to sheath the dock with i-inch creosoted 

 hemlock boards well secured with galvanized nails. This has been found 

 entirely satisfactory to protect these docks from toredo and worms and 

 the custom in eastern waters has been to leave them in the water for seven 

 years before taking them out to replace any sheathing which may have 

 become detached. 



The largest floating dry dock on the Pacific coast for many years was 

 the Quartermaster's Dock in Puget Sound. This dock was built of timber 

 in 1892, and while it has been exposed in what is considered to be very bad 

 water for toredo since its construction, it was in excellent condition when 



