Engineering Wonders of the World
Volume I
År: 1945
Serie: Engineering Wonders of the World
Sider: 448
UDK: 600 Eng -gl.
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174
ENGINEERING WONDERS OF THE WORLD.
possible. This necessarily involves the wider
consideration of the principles expressed in
every modern dock system.
Sites. . £ •
As m other branches or engin-
eering, the designer is not at liberty to select
the most suitable site, nor is he free to utilize
the site imposed upon him strictly in accord-
ance with the ideals of pure science. Not only
is the community, whose industry has created
the necessity for the docks, in existence, but
it is linked by road, river, and rail with all the
other national centres of activity. The neces-
sary docks must therefore be constructed as
near as possible to the bases of these lines of
communication. To involve the problem fur-
ther, it may happen that the most convenient
site is the most difficult, and, consequently, the
most expensive to work. Here the success of
the engineer must obviously be a compromise
between ease of access from the landward side
and minimum capital cost.
Even where there are no difficulties of the
character indicated—where the site is conven-
ient and the ground easily worked—tides may
be the factor of most importance. The cases
of Liverpool and Glasgow are typical. Both
these ports are on rivers ; yet a tidal range of
thirty-one feet has made wet docks obligatory
on the Mersey, while a tidal variation of about
half that range has permitted tidal docks on
the Clyde. No two dock problems are, in
fact, soluble in the same way.
The essential difference between a wet dock
and a tidal dock is that, whereas by means of
gates like those on the locks of a canal the
water in a wet dock is maintained at a uni-
formly high level, the water in a tidal dock is
free to rise and fall through, an open passage
with the flow and ebb of the tide. Further on
we shall deal with locks and lock gates. At
this stage it is necessary to explain the pur-
pose served by docks generally. We know, of
course, the uses to which they are put, but we
are not perhaps quite so certain as to why
THE 925J FEET CANADA DRY DOCK, LIVERPOOL, THE LONGEST OF THIS TYPE IN THE WORLD.
CONSTRUCTED FOR THE LARGEST ATLANTIC LINERS.