64 FI.OATING DRY DOCKS IN THE UNITED STATES. 



examined by the writer last winter, although on account of its dimensions 

 it has never been removed from the water. 



At the time of the construction of the pontoon dock with steel wings, 

 a very thorough investigation was made as to the preservation of the steel 

 wings by painting. This resulted in the use of a graphite paint of well 

 known manufacture. The cleaning and painting was done in the most 

 thorough manner by day's labor under skilled direction and when it was 

 completed everyone expected the most satisfactory results. The outcome, 

 however, was very disappointing. After two and a half years, the interior 

 of the wings is now being coated with bitumastic composition and the outside 

 will be painted with red lead and oil. None of the pontoons in the mean- 

 time have been removed from the water nor have they required attention 

 in any manner. 



All the writer's experience with floating dry docks and their construc- 

 tion and repair leads to the firm conclusion that for under- water work, such 

 as pontoons for the Rennie type of dock, wood is a much superior material 

 of construction to steel, that the original cost is much less, the cost of 

 maintenance less, and the life of the structure greater than steel. For the . 

 wings and upper work, experience is equally conclusive for the use of steel. 

 While it is apparent that the cost of maintenance will be considerable, the 

 structure will last much longer, and, with a sectional pontoon dock where 

 the wings are accessible at any time and any portion of the wings may 

 be entirely replaced if necessary, it would seem that the structure as a 

 whole will last indefinitely. 



So far as the writer is able to judge by a somewhat limited experience, 

 the only reliable protection for interior steel work of floating dry docks 

 in salt water is the bitumastic compound above referred to, but the first 

 cost of this protection is very great, being in the neighborhood of $6 per 

 ton of steel for interior protection only. Any discussion which would bring 

 to bear additional information upon this particular subject would be very 

 much appreciated, and it is to be hoped tlaat the experience of the United 

 States Government with the floating dry dock Dewey at Manila will be 

 of help. 



A comparison of the materials used for wooden and steel pontoons shows 

 that the weight of the steel per hundred tons of lifting power is 33 tons 

 and the weight of wood per hundred tons of lifting power is 36 tons. It 

 is evident that the difference in weight must be supplied by increased 

 dimensions of the wooden pontoons. Other than in this particular, wood 

 appears to have the advantage in every way. 



While reference has been made to a pontoon dock of 7,000 tons lifting 



