A Treatise On The Principles And Practice Of Dock Engineering

DESIGN OF FLOATING DOCKS. 481 stable than the depositing dock, though the latter is, of course, well within the limits of practical safety. Another difference between the two types is that the off-shore dock is constructed in one continuons pontoon, which is a lighter form of construction than the separate caissons of the depositing dock. Design of Floating Docks. The design of floating structures being the particular province of the naval architect, it is manifestly outside the range of the present work to enter into a discussion of any of the specific problems or details connected with the disposition and arrangement of floating docks. The broad prin- ciples of the equilibrium of floating bodies have already been enunciated, in connection with the subject of dock caissons, in Chapter viii., and it would certainly be inadvisable to do more than supplement the information therein contained by a few remarks of a general nature, relating to the subject at present under considération. In the first place, then, with a given length and displacement, an increase in breadth means an increase in stability, hence a broad beam is an advan- tage to a floating dock. The usual proportion of beam to draught lies between 8 and 10 to 1. Fig. 465. Fig- 466- Secondly, a rectangular transverse section has a lower centre of gravity than a curved section, and therefore is more stable. It has already been pointed out that docks with elliptical or U-shaped profiles were fitted with gates; the object of these is to lower the centre of gravity. Thirdly, the less the height of the sides, consistent with the require- ments of shoring, the less tendency there will be to top-heaviness, with the concurrent advantages of greater light and ventilation in dealing with vessels to be repaired. Lastly, the more compartments in a cross-section, the greater the stability under wat’er ballast. This is evident from figs. 465 and 466, which repre- sent two floating tanks containing water, and slightly displaced. The distribution of the water after displacement is much more uniform in the subdivided tank than in the other, and there is also less surging motion.