494
DOCK ENGINEERING.
and 15 feet long respectively. The main cradle consiste of three lines of
longitudinals, supported upon rollers, travelling on six lines of rails,
carrying seven pairs of cross pieces or bilge-cods. The centre longitudinal
is made up of two 10-incli by 6-inch pitchpine timbers, bolted together with
a 5-inch by If-inch flat iron bar between them, and 5-inch by 1^-inch bars
on each side. The central iron bar runs the whole length of the main and
auxiliary cradles, and is increased to 2J inches thickness above the first
section of the main cradle. The side bars run through to within 26 feet of
Figs. 484 and 485.—Plan and Elevation of Slipway at Dover.
SECTION C. O.
Figs. 486 and 487.—Dover Slipway.
the bottom of the cradle. The centre longitudinal is supported by 83 pairs of
rollers, placed directly underneath the main cradle, and the auxiliary cradles,
by rollers about 3 feet apart. At the centre portion of the main cradle, the
side supports are formed of 12-inch by 5-inch longitudinals, carried by two
pairs of rollers under each bilge-cod at the upper and lower ends; the
longitudinals are jointed on the inside, so as to bring them directly over
the inner rails of the outer pairs, and they are carried by two single rollers
on each side, under the bilge-cods.