Docking Facilities

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DOCKING FACILITIES

Transcript of Docking Facilities

DOCKING FACILITIES

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DOCKS• Docks are enclosed areas for berthing the

ships to keep them afloat at a uniform level to facilitate loading and unloading cargo and passengers.

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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.

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Classification of wet docks

• Wet docks in tidal basins: Ports in open sea coast protected by an out lying breakwater, basins are provided within the shelter to reduce the changes in water level due to tides

• Wet docks enclosed or impounded basins: Docks are enclosed and are shut off by entrances or locks and gates to maintain a fairly uniform level of water.

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Advantages of tidal basins:• Vessels can come in and berth or leave at all

times.• Costly arrangements like lock gates are not

required.

Disadvantages of tidal basins: • If the range of tide is more, the operations of

loading and unloading are seriously affected• The fluctuations inwater level will cause the

rubbing effect of sides of ships against berths.

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Advantages of enclosed wet docks: • Uniform level of water is maintained which is very

convenient ' for handling cargo. • Prevents the rubbing of the ships' sides against

the quay walls. • Effect of storms in the outer sea and harbour do

not obstruct the dock enclosure.

Disadvantages of enclosed wet docks: • Requirement of costly arrangements like locks

and lock gates.• Time required for entry and exit of ship is greater

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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.

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Form and arrangements of basins and docks

Approaches to basin and docks Should be sheltered. Must have adequate length. Dredging may be required to keep the approach navigable. In certain ports docks are approached only during high tide

because of very low water level during low tides.

Depth of docks and basins Should be able to accommodate the largest ships visiting

a port. Should be able to deepen the basins if required without

disturbing the foundations of the dock walls.

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• 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 following are the shapes may be adopted as per site conditions:o Rectangular docko Diamond docko Inclined Quay type.

Rectangular dock: The length and breadth should be adjusted in such a way as to give maximum quayage.

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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.

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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.

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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.

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Design and construction of basin or dock walls

• Dock walls are designed as gravity retaining wall sections. It should satisfy the following conditions: Dock empty to withstand pressure of back fill. Dock full with back fill removed. Thickness at top should be sufficient to resist the shock

of contact with ships. Dock walls have to carry additional concentrated loads

like crane foundations, and capstans or bollard fixtures for mooring ships.

Surcharge loads in the shape of loaded vehicles or trains on the quay adjacent to the wall.

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2.10 m

7m

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Other aspects of construction details

• Basin walls have to be of much great height than dock walls to allow for the variation In water levels due to tides.

• As the water level has to be kept constant the sides and bottom should be made impervious and arrangements must be made to supply any loss of water by leakage.

• The front face is generally straight or has a very slight batter for ships to stand close to the wall.

• The front face is given a granite fending surface or timber or steel fender to protect the face of the wall from abrasion of ships.

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• Material for construction: Dock walls are constructed of masonry, brickwork or concrete or a combination of these materials (with construction joints as in the case of concrete walls).

Dock entrancesShips can enter a dock either directly or through Jocks. In either case gates are provided for the dock entrances.The types of gates used are:• Wooden or Iron gates.• Caissons.

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1. Wooden or iron gateso Adopted for locks.o Two pairs o gates are required for operation.o Iron gates is suited for large gates and can be easily adapted.o Wood is elastic and cane undergo sudden shocks.o Iron is liable to rapid corrosion in sea water and is prevented by careful

painting.o Wood is liable to teredo (marine borers) attacks and is prevented by

using greenheart wood.

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Caissons for dock entrances: Two kinds of caissons are employed:

o Sliding caisson.o Ship caisson.

• Sliding caisson: It consists of a box shaped steel structure stiffened internally with proper bracing. It is provided with steel keels sliding on smooth granite floor. Instead of the keel, the caissons could be moved on rollers and rails. The entrance is opened by hauling the caisson into a recess provided in the side of the dock. The caisson also serves as a bridge across the dock entrance.

• Ship caisson: Resembles the outline of a ship in cross-section and is constructed of steel with stiffeners at proper intervals. It is floated into position and sunk into specially prepared grooves in the dock sides and sill. The sinking and raising of this caisson is done by ballasting and unballasting respectively.

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Sizes of dock entrances

Sizes of dock entrances: The width of entrances depends on the largest ship the dock has to receive. Modern ships have widths up to 30m nearly, and to accommodate the largest ship the entrance will have to be sufficiently wide for this purpose.

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Difference between Port,Harbour and

Dock• Dock: A dock is an enclosed area of water

used for loading, unloading, building or repairing ships. Such a dock may be created by building enclosing harbour walls into an existing natural water space, or by excavation within what would otherwise be dry land.

• Harbour: A  harbour or haven, is a body of water where ships, boats, and barges can seek shelter from stormy weather, or else are stored for future use.

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• Port:A port is a location on a coast or shore containing one or more harbuors where ships can dock and transfer people or cargo to or from land. Port locations are selected to optimize access to land and navigable water, for commercial demand, and for shelter from wind and waves. Ports with deeper water are rarer, but can handle larger, more economical ships.

Harbors and ports are often confused with each other. A port is a facility for loading and unloading vessels; ports are usually located in harbors

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