FLOATING DRY DOCKS IN THE UNITED STATES. 69 



case of an iron floating dock in Spain, dating from, I believe, 1858, and still in 

 apparently good condition, though not of the self-docking type. The question 

 therefore resolved itself into one of almost negligible maintenance as to steel on 

 the one hand as contrasted with comparatively short life and continually advanc- 

 ing prices of wood as used in dock construction, on the other. The question of 

 excavation was largely eliminated because of the side-launching method prevail- 

 ing on the lakes, and with which the members are familiar, enabling the use of the 

 same slip for both dry dock and laimching berths. In fact, it is a common practise 

 to launch even the largest ships, up to 600 feet in length and 60 feet beam, sidewise 

 into the ordinary basin dock having a top width of about 100 feet. 



At that time, 1902, there were on the lakes only four ships of 500 feet in length 

 and the tendency seemed to be toward a somewhat shorter ship. We therefore 

 decided that a length of 450 feet was all that we were warranted in providing for, 

 and we accordingly fixed up the sectional sea-docking type consisting of three 

 sections, each approximately 150 feet in length, to which a fourth section was 

 added later. In fact, before the three sections as originally planned were built, 

 we ourselves were building ships of considerably over 500 feet in length. 



Still later, to provide extra flexibility, two other shorter sections were built. 

 The Ecorse dock is, therefore, so far as my information goes, the largest floating 

 dock in the world in respect of linear dimensions, though not as to lifting capacity. 

 The latter is not an important requirement in mercantile work because tmder- 

 writer's restrictions prohibit docking a loaded vessel except at owner's risk. So 

 far as relative endurance of wood and steel is concerned, at least in fresh water, 

 the life of a steel or iron dock is entirely tmknown, while that of a wooden basin 

 or floating dock is fairly well established. 



Mr. DoNNEi<iyY: — Replying to Mr. Penton's discussion, I would say that the 

 very slight action of fresh water upon iron and steel has been thoroughly estab- 

 lished, and it is practically certain that for fresh water very little deterioration 

 in steel structures need be anticipated. In fact, very few vessels on the Great 

 Lakes are painted on the outside below the water-line, and this fact in itself divides, 

 by more than one-half, the necessity for dry docks in fresh water. 



Civil Engineer Leonard M. Cox, U. S. N.. Associate (Communicated): — 

 The writer is particularly interested in Mr. Donnelly's timely paper owing to the 

 fact that he was closely associated (as an observer only) with the timber-steel 

 Robins dock throughout the period of construction and test, having been desig- 

 nated by the Navy Department, on Mr. Donnelly's invitation, to visit the dock as 

 often as necessary and to report in detail upon the type. It is a privilege to dis- 

 cuss a paper which describes a real advance in the development of any particular 

 type of structure, and it must be apparent that the design of the Robins dock 

 marks a very definite step forward. 



Speaking broadly, the life of a modem self-docking steel floating dock should. 



