ocks; for,
though the access of vessels is also governed by the depth of the
approach channel, this channel is often capable of being further
deepened to some extent by dredging; whereas the entrance, formed of
solid masonry or concrete, cannot be adapted, except by troublesome and
costly works sometimes amounting to reconstruction, to the increasing
dimensions of vessels. Accordingly, in designing new dock works with
entrances and locks, it is essential to look forward to the possible
future requirements of vessels. The necessity for such forethought is
illustrated by the rapid increase which has taken place in the size of
the largest ocean liners. Thus the "City of Rome," launched in 1881, is
560 ft. long, and 52-1/4 ft. beam, and has a maximum recorded draught of
27-1/2 ft.; the "Campania" and "Lucania," in 1893, measure 600 ft. by 65
ft.; the "Oceanic," in 1899, 685-1/2 ft. by 68-1/4 ft., with a maximum
draught of 31-1/3 ft.; the "Baltic," in 1903, 709 ft. by 75 ft., with a
maximum draught of 31-3/4 ft.; and the "Lusitania" and "Mauretania,"
launched in 1906, 787-1/2 ft. by 88 ft.

Dimensions of entrances and locks.

The width and depth of access to docks are of more importance than the
length of locks; for docks which are reached through entrances with a
single pair of gates have to admit vessels towards high water when the
water-level in the dock is the same as in the approach channel, or
through a half-tide basin drawn down to the level of the water outside,
and are therefore accessible to vessels of any length, provided the
width of the entrance and depth over the sill are adequate; whilst at
docks which are entered through locks, vessels which are longer than the
available length of the lock can get in at high water when both pairs of
gates of the lock are open. Open basins are generally given an ample
width of entrance, and river quays also are always accessible to the
longest and broadest vessels; but in a tidal river the available depth
has to be reckoned from the lowest low water of spring tides, instead of
from the lowest high water of neap tides, if the vessels in the open
basins and alongside the river quays have to be always afloat.

Many years ago the Canada lock at Liverpool, the outer North lock at
Birkenhead, the Ramsden lock and entrance at Barrow-in-Furness, and the
Eure entrance at Havre, were given a width of 100 ft. Probably this was
done with the view of admitting paddle steamers, since