RECENT DEVELOPMENTS IN SHIPYARD PLANTS. 177 



makes provision for a very great increase in the length as compared to vessels which 

 have been so far constructed in this country, and involves the consideration of 

 launching weights and facilities suitable for vessels of these great lengths. So far 

 as the Navy Department designs are concerned, the capital slips have all been pro- 

 vided with an average inclination of slips of one-half inch per foot, provision being 

 made for launching on a camber, the actual declivity of the building slips being 

 seven-sixteenths inch per foot for the upper half and nine-sixteenths inch per foot 

 for the lower half of the slip. The design of these slips contemplates the use of 

 concrete throughout, though in a number of cases, due to lack of time or money, it 

 has been necessary to substitute wood pile construction. With concrete slips of this 

 great length, and the height that necessarily must be reached at the upper end of the 

 slip, provision can be made for utilizing a very considerable area underneath the slip 

 for stowage purposes and for carrying on such classes of work as can most advan- 

 tageously be done in the immediate vicinity of the vessel under construction. 



An interesting type of building slip, which perhaps is the first of its kind, at least 

 on such a large scale, has been provided at one of our navy yards, where a shallow 

 dry-dock has been constructed with a depth over the blocks at mean high water of 

 20 feet. The dock has essentially the same dimensions as the other capital slips, pro- 

 viding for a vessel slightly under 1,000 feet long and of a beam of 1 10 feet, and in the 

 details of construction resembling other large dry-docks, except that the draught is 

 very much reduced. The caisson will be of the usual type ; provision will be made 

 for pumping out the dock, but at a very much slower rate than would be needed if 

 it were to be normally used as a dry-dock. With this arrangement, the weight hand- 

 ling facilities could be of any type that might be selected for the normal type of slip. 

 In this particular case, the cranes are to be of the traveling, rotating, hammerhead 

 type, with a capacity of 15 tons at 85 feet radius, electrically driven. The ad- 

 vantages which we look forward to in this construction are, first, of course, the 

 elimination of the risk and expense of launching, and second, the facilitating of the 

 erection, due to building on an even keel, and the elimination of the difficulties inci- 

 dent to delivering men and materials at the height of a vessel when built on an in- 

 clination. In addition to being on an even keel, the vessel will be very much lower, 

 approximately 50 feet, and the height of the weight-handling cranes can be corre- 

 spondingly reduced. If the conditions at the yard at the time make it desirable, the 

 vessel can be carried to any degree of completion prior to launching, with the only 

 limitation that the draught cannot exceed the depth of water over the blocks. The 

 other side of the picture is the increased cost, which in this particular case, owing to 

 the sub-soil conditions, not requiring piling, is not expected to be materially greater 

 than in the case of the usual form of slip. For naval purposes, a building slip of 

 this type has a further value, in that considerable periods of time may elapse dur- 

 ing which building work is not carried out, and the slip will then be available for use 

 as a dry-dock or a wet slip for small vessels. 



