54 PORT ECONOMICS
craft, but they are inadequate for dealing with vessels
of the larger calibre engaged in overseas commerce. The
principles governing selection as between dry docks and
floating docks have been stated in Chapter II.
The dimensions of such structures are not easy to
determine. The larger they are, the more costly they
become, and the less the number of occasions on which
they will be utilized to full capacity. Obviously, it is
wasteful in first cost to construct, and in pumping cost to
employ, say, an Soo ft. dry dock for a 6o0o ft. ship, but
unless the dock is large enough for the 750 ft. ship, which,
perhaps, also visits the port, that ship will have to go
elsewhere for its repairs to be executed, thus losing money
to the port and lowering its prestige. On the other hand,
it must be recognized that the occasional accommodation
of the 750 ft. ship involves an outlay which must be
recouped in some way from the great bulk of the port’s
clientéle. In the expectation of vessels of more than
1,000 ft. in length, a considerable number of graving
docks exceeding this figure have been constructed, but as
yet there has been no occasion to use them to anything
approaching their full capacity.
Again, it is often a difficult, and certainly always an
expensive, matter to enlarge a dry dock. Practically,
apart from entire reconstruction, such docks can only be
lengthened (supposing space to be available). And if the
length be increased, it may become disproportionate to
the width and depth. Hence, the policy of building a
moderate sized dry dock is beset with the impracticability
of enlarging it to meet growing requirements.
While the port authority provides dry docks, it has
no monopoly of them. Many private firms engage in
ship repairing, and construct their own docks for use in this
connection. Shipbuilding concerns commonly have a dry
dock available. This being so, the port authority have to
submit to all the restrictions imposed by competitive rates
of letting, though, generally speaking, private firms do
