THE SECTIONAL AND BALANCE DOCKS.
479
“The Sectional Dock, as its name implies, is divided into as many
sections as are required for the particular vessel to be docked. Each
section consists of a rectangular wooden box made watertight, and in the
ends of these there is an open wooden framework of a height somewhat
greater than the depth to which it is proposed to sink the dock. Within
this frame a wooden watertight box slides up and down, which can be fixed
by means of a rack and pall to any required position. These boxes or
tanks serve the purpose of keeping the base or lower part of the dock
steady, water not being allowed to enter therein. Thus, a complété dock
consists of a series of eight or ten independent compartments below, with
two movable air chambers to each ; and, although there are certain timbers
connecting the different boxes, they are not constructed so as to enable any
box to support the adjoining ones.” *
A disaster occurred to one of these docks at Callao, involving the
sinking of a ship, by reason of the disconnected compartments yielding to
The Balance Dock is an attempt at improving the sectional dock.
There is only one compartment, subdivided internally into a series of
separate chambers. Docks constructed on this principle have generally
been successful, and have had considérable vogue in the United States.
Iron docks came in about the year 1859. They were introduced by
Mr. Rennie at the naval arsenal at Cartagena, and based on the principle
of the balance dock of Mr. Gilbert. A transverse section of the Cartagena
Dock is shown in fig. 462. It had a length of 324 feet, a breadth of
105 feet, and a lifting power of 11,500 tons.
In 1860, the elliptical, or U section, which had disappeared with the
earliest timber types, was reproduced in the Bermuda Dock, and continued
to be adopted at intervals. At the present time, the rectangular shape is
almost the invariable rule. The U section was generally fitted with gates
* Rennie on “ Floating Docks,” Min. Proc. Inst. G.E., vol. xxxi.