SHIP CAISSONS.
357
oak complété the general features of the caisson, which was constructed
in 1878 from designs by Messrs. Kinipple and Morris.
That a caisson of this type is not necessarily rectilinear in plan is
evidenced by the instance of a caisson (fig. 339), designed in 1864 by the
Fig. 339.
late Mr. W. R. Kinipple, and built the following year for a graving dock
at Limekiln, London. Beyond the eccentricity of its form, inspired by the
desire to obtain the axial advantage of a mitred sill, there is nothing very
remarkable about its construction. As in the preceding case, it is furnished
with a lower air-chamber and two watertight bulkheads, which latter,
however, pass right through the air-
chamber and completely trisect the
caisson.
Ship Caissons have more or less the
form of an ordinary navigable vessel, but
the curvature of their sides varies very
much with the depth of water in which
they have to float. At the Bute Docks,
Cardiff, where the draught of water on
occasion is as little as 91 feet, the caisson
has had to be designed with sufficient
buoyancy space at that deptli to support
the upper weight. This and the necessity
for a margin of stability, has necessitated
the somewhat peculiar profile shown in
fig. 340.
Fig. 340. —Ship Caisson at Cardiff.
The more general section of ship caisson is similar to that in fig. 341,
which is the section of one at the Kidderpur Docks, Calcutta.* A plan
and elevation are given in figs. 342 and 343. The keels and stems of the
caisson are faced with greenheart.
A caisson differing somewhat in construction and internal arrangements
is that (fig. 344) closing the entrance to the Alexandra Graving Dock at
Belfast,! a short description of which is appended.
* Bruce on “The Kidderpur Dock, Calcutta,” Afin. Proc. Inst. C.E., vol. cxxi,
+ Kelly on “The Alexandra Graving Dock, Belfast,” Min. Proc. Inst. C.E.,
vol. cxi.