Docks and their classification

DOCKS AND THEIR
CLASSIFICATION

 Docks:
Docks are enclosed areas for berthing the ships
to keep them afloat at a uniform level to
facilitate loading and unloading cargo.
A dock is a marine structure for berthing of
vessels for loading and unloading cargo and
passengers.
Docks are necessary for discharging of the
cargo as ships require a number of days for
discharging cargo, during which period they
need a uniform water level. If ship is subjected to
a vertical movement by the tides, great
inconvenience will be felt in lifting the cargo
from the ship and special arrangement will be
needed for lifting the cargo.

 Classification of Docks:
Docks can be classified into following two
categories:
 Wet docks.
 Dry docks.
Wet docks: Docks required for berthing of
ships or vessels to facilitate the loading and
unloading of passengers and cargo are called
wet docks. These are also known as harbor
docks.

 Dry docks:
The docks used for repairs of ships are known
as dry docks.

 Shape of docks and Basins:
Shape of dock or basin should be straight
to facilitate the ships to stand along them, as
curved shape is not convenient for ships to
stand along side.
The shape of docks and basins should
be such that maximum quayage i-e berthing
length is available within the given area. The
shape has therefore essentially to be made up
of a number of straight patterns as curved
lines are unsuitable for berthing of the ship.

 The following are the shapes may be adopted
as per site conditions:
 Rectangular dock
 Diamond dock
 Inclined Quay type.
Rectangular dock:The length and breadth
should be adjusted in such a way as to give
maximum quayage

 Diamond Dock:
For the same perpendicular distance
between long sides, the long side could be
extended conveniently.
Inclined Quay dock:
It consists of a number of projecting quays
into the dock or basin.

 Location of dock:
Docks can be located on inland ports of
rivers or at estuaries or open sea coasts. A
proper piloting service is necessary. The river
approaches to the dock have to be
maintained.
 Internal arrangements:
Generally different docks are required for
different types of cargo. For example coal
and oil should be deal with separate way from
food or general cargo.

 Other aspects or requirements:
 Approaches must be of sufficient depth and
sheltered. In many cases approach channels
both on the open coast and island docks have
to be dredged frequently.
 Availability of fresh water to replace fouled
and leaked water from docks.
In inland to replace the fouled water from
docks, separate canals from the rivers have to
be provided, if alternate sources of water
supply are not available. In case of sea coast
docks, the sea water could be used for
cleaning and replenishing the dock.

Classification of Dry docks:
Dry docks are classified in the following
five categories:
 Graving or dry docks.
 Floating dry dock.
 Marine railway dock.
 Ship lift dry docks.
 Slip ways.

 Dry or graving dock:
A dry dock is also known as graving dock. It
is long excavated chamber, having side walls,
a semi circular end wall and a floor. The open
end of the chamber is provided with a gate
and acts as the entrance to the dock.
 Floating dry dock:
It may be defined as a floating vessel, which
can lift ship out of water and retain it above
water by means of its own buoyancy. It is a
hollow structure made of steel or R.C.C
consisting of two walls and a floor with the
ends open.

To receive a vessel or ship for repair, the
structure or floating dock is sunk to the
required depth by filling water known as
ballasting in its interior chambers and the
vessel is then floated into position and
berthed. The dock is raised bodily with the
berthed vessel by un ballasting the chambers
by pumping out the water. The earliest
floating dry docks resembled the shape of
ships.

 Marine railway dock:
The marine railway or slip dock or slip way
is an inclined railway extending from the
shore well into the water as the off there. This
railway track is used to draw out a ship
needing repair out of the water.
Components of a marine dock:
The essential parts of a marine dock are as
follows:
 Cradle.
 Track.

 Cradle: The cradle or platform is constructed
of steel and moves up and down on an
inclined track. The cradle is mounted on a
system of rollers which move on the iron
tracks laid on longitudinal timbers. These
beams resting on piles and other firm
foundations.
Track: The track consists of heavy rail sections
secured to longitudinal sleepers supported on
cross ties and laid at inclination varying from
1/12 to 1/25, usually an inclination of 1/15 is
found convenient and useful.

 Lift dry dock:
This is a constructed platform capable of
being lowered into and raised from water.
Lowering and raising is achieved by means of
hydraulic power applied through cylinders
supporting the ends of cross girders carrying the
platform.
 Ship lifts:
As the name suggests, in the ship lift, the
ships are lifted bodily out of water. The ship lifts
may be either electric, hydraulic or pneumatic.
These lifts are used for launching as well as for
dry docking the ships. Their main advantage is
the ease in adaptability to transfer system
enabling multiple garaging of ships.

 Slipways: This technique is used for repairs as
well as for building of vessels. In its simplest
form a slip way consists of a inclined path of
timber or stone laid on a firm ground. On this
inclined path a series of rails are fixed. The
rails run up from a sufficient depth of water to
the required height above the high water
level to a point at which the longest vessel to
accommodated is completely out of range of
tide. The lower end of slip is tidal and open to
water.

Docks and their classification

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Docks and their classification