PORT ECONOMICS
In navigating the approaches to the port, the services
of a pilot will probably be required—in most cases they
are compulsory. This means, in practice, that if a pilot
boat presents itself, a pilot must be engaged, but there is,
at present, no obligation on the part of the master of a
vessel to go out of his course in order to find a pilot. The
river, or channel, pilot having boarded the vessel in the
open sea, will have brought the vessel as far as the inner
harbour. During this period he is in sole charge, and the
captain is under his orders. At the dock entrance, however,
 a change generally is made and a dock pilot will
probably take over the duty of manceuvring the ship into
the berth assigned. During her passage through the lock
and the dock as far as her berth, the vessel will probably
engage the assistance of tugs in addition to her own propelling
 power.
In the case of a vessel having to enter the dock after
the open tidal period, the process of locking in is as follows.
As stated in Chapter II, the lock chamber has two pairs
of gates (this is a minimum ; there may also be a third
intermediate pair to divide the chamber into two parts
for the economical reception of smaller sized vessels),
and the inner pair having been closed, the ship is
manceuvred into the chamber and the outer gates are
brought together. Water is then admitted to the chamber
through sluices in the side walls or in the gates, until the
level of the water in the chamber has been raised to the
level of the water in the dock. The inner gates are then
opened and the vessel is free to enter the dock.
It is economical at this stage to have another vessel
ready to pass out, for the loss of one chamberful or
“Jockful ” of water from the inner dock then serves for
the passage of two vessels. When there is an appreciable
difference in level between the dock and the river, and the
lock chamber is of considerable size, the economy of water
is important.
At the entrance lock, the ship comes under the control

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