A

REPORT

ON

HARBOUR AND DOCK

SUBMITTED BY GUIDED BYMEHTA PARTH K. Ms. PARUL PATEL08BCL023MODI DHRUNAD08BCL026

CIVIL ENGINEERING DEPARTMENTINSTITUTE OF TECHNOLOGY

NIRMA UNIVERSITY OF SCIENCE AND TECHNOLOGYAHMEDABAD.

AUGUST-2009

CERTIFICATE

This is to certify that Mr. MEHTA PARTH KIRANKUMAR

(Roll No. 08BCL023) & MODI DHRUNAD (Roll No.

08BCL026) completed his report on “HARBORS AND DOCKS”

as a part of the requirement of Special Learning Programme 3 th

semester.

Date: 09/10/2009

Place: AHMEDABAD

MS.PARUL PATEL

CIVIL ENGINEERING DEPARTMENTINSTITUTE OF TECHNOLOGY

NIRMA UNIVERSITY OF SCIENCE AND TECHNOLOGYAHMEDABADAUGUST-2009

ACKNOWLEDGEMENT

It is indeed a great pleasure for me to thank those who have always helped me

throughout seminar presentation as a part of 3rd semester.

First of all, I would like to thank my guide Ms. Parul patel, who helped in pinpointing

the need of this seminar, stimulating suggestions and encouragement in all the time

of research and also for writing of this report. I am sincerely thankful for him

valuable guidance and his help to enhance my presentation skills.

I would also like to thank our Head of the Civil Engineering Dept. for giving me this

great opportunity and also to the management of Nirma Education and Research

Foundation (NERF) for providing excellent infrastructure and internet facilities

whenever and wherever required.

Finally, I am thankful to all faculty members of the Civil Engineering Department for

helping me. I am thankful to Library staff and all my friends and colleagues who

have directly or indirectly helped me during this seminar work.

Mehta Parth k.

08BCL023.

Modi dhrunad

08BCL026

ABSTRACT

Roadways and railways are common means of transportation on land while

waterways are common since hundreds of years, for travelling between different

countries connected by seas and oceans. Air travel is common through airways. All

means of transportation need place of approach for using them, e.g. railway

stations are necessary for use of railways, bus stops are required for use of

roadways. Aerodromes are constructed for using airways, while harbours are to be

developed for use of waterways.

Air travel is heavily costly, though it covers entire earth surface for its use; hence

cannot be adopted as common means of travel. Movement on land is easy through

roadways and railways but area available is nearly one-third of entire earth surface.

On the contrary two-third of entire earth-surface is covered by water which proves

importance of waterways or water transportation. Also It becomes cheapest mode

of transportation.

This paper gives the introduction of Harbour Structure along the cost and idea of

docks structures.

INDEX

No. TABLE OF CONTENT Page

1.0 HARBOUR

2.0 TYPICAL LAYOUT OF HARBOUR

3.0 ACCESSIBILITY AND SIZE OF HARBOURS

4.0 DOCKS

5.0 CLASSIFICATION OF WET DOCKS:

6.0 FORM AND ARRANGEMENTS OF BASINS AN DOCKS

7.0 DESIGN AND CONSTRUCTION OF BASIN DOCK WALLS

8.0 REPARING OF DOCKS

9.0 CONCLUSION

HARBOURS

Harbour can be define as a basin or haven of navigable waters well protected

naturally or artificial from action of wind and waves, and is situated along sea-shore

or river or canal connected to sea.

Basin is a water reservoir of required area. It is said to be navigable when depth of

water in basin is greater then draft required for largest ship, likely to visit the

Harbour.

Draft is the vertical linear immersion of ship below water surface for the ship to float

in stable condition safely. Safe floating requires a standard vertical clearance

between bottom part of ship and sea bed.

CLASSIFICATION OF HARBOUR

The Harbours are classified as under:

(1) Classification depending upon the protection needed

(2) Classification depending upon the utility

(3) Classification based upon the location.

Classification depending upon the protection needed

Depending upon the protection needed, Harbours are broadly classified as:

(a) Natural Harbour

(b) Semi-Natural Harbour

(c) Artificial Harbour.

(a) Natural Harbour

Natural formations affording safe discharge facilities for ships on sea coasts, in the

form of creeks and basins, are called natural Harbours.

The factor such as local geographical features, growth of population, development

of the area, etc. have made the natural Harbour big and attractive. Bombay and

Kandla are example of Natural Harbour.

In other words, natural Harbour is an inlet protected from storm and waves by

natural configuration of land as sown in figure.

(b) Semi Natural Harbour

This type of Harbour is protected on sides by headlands and it requires man made

protection only at the entrance as sown in below figure. Vishakhapatnam is the

semi natural type of Harbour.

(c) Artificial Harbour

Where such natural facilities are not available, countries having a sea board had to

create or construct such shelters making use of engineering skills and methods, and

such Harbour are called artificial or man-made Harbours.

Classification depending upon the utility

Depending upon their utility, Harbours are further classified into five major types:

(a) Harbour of refuge

(b) Commercial Harbours

(c) Fishery Harbours

(d) Military Harbours

(e) Marina Harbours.

(a) Harbour of Refuge

On dangerous coast-lines, disabled or damaged ships, under stress of weather

conditions will need quick shelters and immediate repairs.

Requirement of Harbour of refuge are:

Ready accessible from the high seas

Safe and convenient anchorage against the sea

Facilities for obtaining supplies and repairs.

All type of naval craft, small and big, will need refuge in an emergency and hence,

such refuge Harbours should provide commodious accommodation. Modern big

ships will require a lot of elbow room for purpose of manoeuvring or turning about.

(b) Commercial Harbour

Commercial Harbour could be situated on coasts or estuaries or big rivers on inland

river coasts. They do not normally have any emergency demand like a Harbour of

refuge and practically the size and number of ships using such Harbours are known

factors.

Basic requirement of commercial Harbour are:

Special accommodation for the mercantile marine.

Ample quay space and facilities for transporting, loading and unloading

cargo.

Storage sheds for cargo.

Good and quick repairs facilities to avoid delay.

More sheltered condition as loading and unloading could be done with

advantage in calmer waters.

(c) Fishery Harbour

Harbour should be constantly open for departure and arrival of fishing ships.

Preliminary requirement are loading and unloading facilities and quick dispatch

facilities for the perishable fish catch like railway sidings and roads and Refrigerated

stores with ample storing space for preserving the catch.

(d) Military Harbour

These Harbours are the naval vessels bases which are meant to accommodate the

naval vessels. They server as supply depot also. Bombay and Cochin Harbours naval

bases.

(e) Marina Harbour

This is Harbour providing facilities of fuel, washing machine, telephone, etc. for

small boat owners, having temporary or permanent berths. In other words, Marinas

as a small Harbour or Boat basin providing dockage, supply and services small

pleasure crafts.

Facilities provided such as Resort, Yatch club for all permanent members of club get

the marina facilities, sports, fishing facilities, etc.

Classification based upon the location

The harbour entrance should be designed and located for quick easy negotiation by

ships overtaken by stroms. It should be narrow enough not to exopse The layout of

a Harbour is greatly influenced by its location and based on the location, Harbour

are further classified into following four major types:

(a) Canal Harbor

(b) Lake Harbor

(c) River or Estuary Harbor

(d) Sea or Ocean Harbor.

(a) Canal Harbor

The Harbor located along the canals for sea navigation and inland, is known as

canal Harbor. It is found that maintenance dredging of canal basin is generally

negligible.

(b) Lake Harbor

The Harbor constructed along the shore of lake is known as Lake Harbor. If the lake

is large, then the conditions are similar to those in ocean expect that tidal action

does not occur.

(c) River or Estuary Harbor

The Harbor constructed along the bank of river is known as river or estuary harbor.

River and Estuary crate the main transportation route to join the hinterland and the

sea.

(d) Sea or Ocean Harbor

The Harbor located on the coast of a sea or an ocean is called the sea harbor. They

are intended for sea going vessels.

TYPICAL LAYOUT OF HARBOUR

Harbor entrance

(a) Location and Orientation

The following factors in the location and orientation of harbor entrances should be

considered:

(1) Water depth: Locate the harbor entrances in an area where the natural water

depth is adequate for passage of the largest ship.

(2) Sheltering: Locate on the lee side from most severe storm waves, and between

overlapping breakwaters.

(3) Channeling external disturbances: Location and orientation will direct any

external wave disturbances to areas of the harbor remote from locations of berthing

and anchorage areas.

(4) Navigation: Navigation through the entrance should be easily accomplished. In

particular, locate so that there will be strong beam currents in the harbor entrance

at all tidal stages.

(5) Littoral drift: Orientation should prevent the entrance of littoral drift into the

harbor. Where possible, the entrance will be located in an area relatively free of

littoral drift.

(6) Multiple entrances: Where possible, provide two entrances with different

exposures, which can be used as alternates depending on the direction of the wind.

Multiple entrances are advantageous in wartime, since they make the harbor more

difficult to block. Double entrances also reduce the velocities of the tidal currents

because of the increased area.

(b) Channel entrance width

Provide minimum channel entrance width consistent with navigation needs. The

approximate requirements of channel entrance width related to size of vessel to be

accommodated are as follows:

Width of Harbor classification entrance, ft

Medium Vessel 300 to 500

Large Vessels 600 to 1,000

(1) Entrance: Except in unusual circumstances, a width of 1,000 feet is ample for

very large container vessels, and under favorable conditions of entry, a width of 800

feet may be considered.

(2) Secondary entrances: For secondary entrances, or those not to be used by large

ships, a width of 300 feet may be considered, provided that entrance conditions are

favorable.

(3) Currents: Entrance widths should be adequate to reduce currents to acceptable

values. The maximum allowable current in the entrance channels is a function of

the type of ship or ships to be accommodated. Except under special circumstances,

current is not to exceed 4 knots.

Typical marina harbor layout

ACCESSIBILITY AND SIZE OF HARBOURS:

Accessibility depends on the location of the harbor. The harbor entrance should be

designed and located) for quick and easy navigation by ships, overtaken by storms.

At the same time, it should be narrow enough; not to expose the harbor to the

effects of the stormy sea. Maximum dimension up to 180 m have been adopted.

The entrance is generally placed with a passage to the interior of the harbor so

arranged as to minimize the effect of rough seas.

Size of harbor depends upon the number and size of ships likely to use the harbor

at one time. Some of the biggest modern ships are 275 m to 300 m long and

about 30 m wide. There should be sufficient area for maneuvering them without

collision. Thus, the size is determined by:

(I) Accommodation required.

(ii) Convenience for maneuvering and navigation.

(iii) Adaptability to natural features.

Regarding the entrance width, the narrower the entrance, the better is the interior

protected, consistent with easy and quick entry or exit of the biggest vessel using

the harbor. Even when the breakwaters are high enough to protect the harbor,

waves from outside the harbor, set up diminutive waves inside the harbor

depending on the entrance widths.

The following empirical formula given by Stevenson a limited application is

sometimes used in the design fib entrances:

h={√ lL−0.027

4√D (1+ lL )}H

inhere H is the height in meters of unrestricted wave at the Entrance mouth of

width I meters, h the reduced height of the diminutive wave inside the harbor at a

distance D meters from the mouth and where the harbor is L meters wide. this

formula is applicable to a distance of 15 m from I the entrance and where the

harbor is well protected by a Cortical sea wall.

(1) Site selection: Great care has to be exercised at the time of making

selection of site for a harbor. The guiding factors which play a great role in choice

of site for a harbor are as follows:

(I) Availability of cheap land and construction materials;

(ii) Transport and communication facilities;

(iii) Natural protection from winds and waves;

(iv) Industrial development of the locality;

(v) Sea-bed, subsoil and foundation, conditions;

(vi) Traffic potentiality of harbor;

(vii) Availability of electrical energy and fresh water;

(viii) Favorable marine conditions;

(ix) Defense and strategic aspects; etc.

(2) Shape of the harbor: While deciding the shape of the harbor, the following

principles should be kept in mind:

(I) In order to protect the harbor from the sea waves, one of the pier heads should

project a little beyond the other.

(ii) Inside the pier heads, the width should widen very rapidly.

(iii) The general shape of the harbor should be obtained by a series of

straight lengths and no re-entrant angle should be allowed

(3) Harbor depth: The channel depth is generally determined by the following

formula:

D=D 1+H3

+ D2

Where D1= draft of largest ship to be accommodated

D2 = allowance for squat of the moving ship

H = height of storm waves

Thus, the harbor and approach channel should be of; sufficient depth to allow

navigation at low water when ships' are fully loaded. It must be ensured that there

are no obstructions like boulders or sunken ships about the required; depth for safe

navigation. The maximum harbor depth below lowest low water is achieved as

follows:

Max. harbor depth = loaded draft + 1.2 m

When bottom is soft

Max. harbor depth = loaded draft + 1.8 mj

when bottom is rock

(4) Marine surveys: It is necessary to collect sufficient- information about the

area before finalising the layout of the harbor and design of its various components.

Following two marine surveys are carried out for this purpose:

(I) Hydrographic survey

(ii) Topographic survey.

Each of the above type of marine survey will now be briefly described.

Hydrographic survey:

This survey becomes easy at places where local testiary and minor

trigonometrical; controls are available. It, consists of locating the shore line

at low_ and high tide level and positions of all structures or obstructions in the

water and along the shore. The depths of the sea

bottom are obtained by the use of fathometer or echo sounder designed for

the hydrographic surveys. The instrument is normally mounted on a motor

boat which is kept along pre-established range line. The recording chart

automatically registers natural profile of the sea bed.

The soundings are taken at 7.50 m intervals along range lines 15 m to 30 m

apart depending upon the nature of the bed and the extent of the details

required.

The hydrographic charts are then prepared and they help navigators to steer

safe courses through channels and thus sub-marine hazards are avoided.

(ii) Topographic survey:

This survey is carried out to obtain ground contours at intervals of 0.50 m to

1.50 m. The higher contour interval is used where the terrain is rough and in

areas where there is little or no construction work of any importance. The

prominent irregularities at 30 m intervals should be carefully examined. In

addition to levels, the topographic survey should include the following

details:

(1) location of existing buildings and other structures;

(2) location of borings and test pits; and

(3) prominent land marks.

(5) Harbor planning: The planning of harbor should be carried out after

collecting the necessary information existing at the proposed site. The important

facts to be studied and scrutinized can be enumerated as follows:

(I) It is necessary to carry out a thorough survey of the neighbourhood

including the foreshore and the depths of water in the vicinity.

(ii) The borings and soundings should be taken to ascertain the

character of the ground.

(iii) The borings on land should also be made so as to know the probable

subsurface conditions on land. It will be helpful in locating the harbor

works Correctly.

(iv) The nature of the harbor, whether sheltered or not, should be studied.

(v) The existence of sea insects which undermine the foundations should be

noted.

(vi) The problem of silting or erosion of coastline should be carefully studied.

(vii) The natural meteorological phenomena shoo are studied at site especially

with respect to require of storms, rainfall, range of tides, maximum and

minimum temperature, direction and intensity: winds, humidity, direction and

velocity, currents, etc.

(6) Features of a harbor: The constituents of' harbor can be

enlisted as follows:

(I) entrance channel,

(ii) approach channel,

(iii) turning basin to allow gradual turning of tm ship,

(iv) berthing basin,

(v) breakwaters,

(vi) quays and wharves,

(vii) jetties and piers,

(viii) docks,

(ix) slipways, and

(x) other ancillaries such as god owns, sheds, buoys lights, fire

protection towers, etc.

The term turning basin is used to mean a water area inside a harbor or an

enlargement of a channel to permit the turning of a ship. Where space is available

the radius of turning basin should be at least equal to" double the length of ship to

permit either free turning or turning with aid of tugs, if found necessary.

However, where the available space is limited, the; ship may be turned by

warping around the end of pier and for such circumstances; it may be of triangular

or rectangular shape.

(7) Defects in harbors: The usual defects whic1 are noticed in the

construction of many harbors can be summarized as follows:

(I) The size of the harbor proves to be small accommodating the

increase in traffic.

(ii) The depth of water proves to be insufficient for-the ships to berth

safely.

(iii) The quay or landing area between the berths is very narrow and there is no

enough room for the cargo to be stored.

(iv) The whole area is congested and hence, the functioning of the harbor

cannot be carried out smoothly.

These defects can easily be avoided if an eye is kept the possible expansion of

the harbor and providing necessary facilities accordingly well in advance.

(8) Requirements of a good harbor: Following are the requirements of a good

harbor:

(I) The ship channels which may either be natural or artificial must have

sufficient depth for the draft of the vessels visiting the harbor.

(ii) The bottom should furnish secured anchorage to hold the ships against

the force of high winds.

(iii) The land masses or breakwaters must be provided to protect against the

destructive wave action.

(iv) The harbor entrance should be wide enough to permit ready passage

for shipping and at the same time, it should be narrow enough to restrict

the transmission of excessive amounts of wave energy during storm. It may

be noted that previously, more emphasis was van on protection works like

sea walls, breakwaters, etc. In recent years the emphasis has been shifted to

the "deepening of channel because of drastic changes in the size of ships.

DOCKS:

Wet docks are enclosed areas for berthing ships, to keep them afloat at a uniform

level, to facilitate loading id unloading of cargo and passengers. Docks are

necessary cause discharging of the cargo of ships requires a number I days during

which period, if the ship is subjected to vertical movement by the tide, great

inconvenience will be caused and special arrangements will have to be made for the

lifting of the cargo. Docks are classified in two categories:

(1) Wet docks

(2) Dry docks

Docks which are used for berthing of vessels to facilitate loading and unloading of

passengers and cargo are known as wet docks and those used for repairs of the

vessels are known as dry docks. The wet docks are sometimes known as the harbor

docks.

location and basin formation

Harbors are prone to be affected by, which may cause changes in the water level. If

at low tides, the level is sufficient as not to ground the ships, the ships could be

berthed in these areas.

CLASSIFICATION OF WET DOCKS:

(1) Wet docks in tidal basins:

Harbors are prone to be affected by tides, which may cause changes in the water

level. If at low tides, the level is sufficient as not

ground the ships, the ships could be berthed in these areas Thus, in ports on the

open sea coast protected by aril outlying breakwater, basins are formed within its

shelter. In these basins, pier walls are projected at right angles to the shore

alongside which vessels can lie and discharge their cargoes.

Dock location of river side

(2) Wet docks in enclosed or impounded basins:

Docks or wet docks are enclosed and are shut off by entrances by locks to maintain

a fairly uniform level of water. Where tidal ranges are very marked and large,"

docks are formed by enclosures. The water level in these enclosures should be

maintained at constant level by providing locks and gates. Basins are partially

enclosed areas of water, which are approached by open entrances and are subject

to fluctuations of levels due to tidal variations. These are also known as medal

basins.

ADVANTAGES AND DISADVANTAGES OF TIDAL WET DOCKS:

(1) Advantages of tidal basins:

(I) Vessels can come in and berth or leave at all times Thus, there is

speedy and unrestricted arrival and departure of ships.

(ii) Costly arrangements like lock gates for the closing of the entrances are

not required.

(2) Disadvantages of tidal basins:

(I) If the range of tide is more, the operations of loading and

unloading are seriously affected.

(ii) The fluctuations of water level will cause the rubbing of sides of ships

against the berths.

The wet docks are useful under the following situations:

(I) In some harbors, there may be heavy silting. The wet dock area is kept freeby

keeping out the turbid water and supplying to it only clears water.

(ii) Where there is considerable difference of level in tides, the ships can enter the

wet dock even though the harbor itself may not be navigable.

ADVANTAGES AND DISADVANTAGES OF ENCLOSED WET DOCKS:

(1) Advantages of wet docks or impounded-basins:

(I) Uniform level of water is maintained which is very convenient for

handling cargo. It increases the commercial activities of port.

(ii) It prevents the rubbing of the sides of ships against the quay walls.

(iii)It obviates the necessity of constant attention to alternation of

mooring.

(iv)Effect of storms in the outer sea and harbor do not obstruct the dock

enclosure.

(2) Disadvantage of wet docks or impounded-bas

The only drawback of wet docks will be that costly arranger will have to

be provided for locks and lock gates and time will be required for entry

and exit for ships.

FORM AND ARRANGEMENTS OF BASINS AN DOCKS:

The exact arrangement and form must depend upon the available site. The object

to be aimed at in the design. Is to obtain the maximum length of quay in

proportion the water area of the basin or dock.

(1) Approaches to basins and docks:

The approach to basins and docks must be sheltered ones and they should be of

adequate lengths also. Most of the ports require dredging to be done so as to keep

the approach navigable The cost of dredging forms an important item in the budget

provisions of any port. In certain ports, docks are approached only at high tides

because the approach channel cannot be navigated at low tides.

(2) Depth of docks and basins:

The depth of dock and basins should be capable of accommodating the large vessel

likely to visit the port. It is possible to deepen on the basins subsequently, if

required, subject to the conditio that the foundations of dock walls are not

disturbed or damaged.

Excavation for docks and basins: If the site of dock or basin is inland, the

excavation is generally Carrie out by hand wagons, excavators, etc. If the site is

partially covered up by the tide, arrangements will have to be made to form an

embankment to keep the sea out. It will also be necessary to provide the

embankment by rubble pitching to prevent the waves from scouring out the

embankment.

(3) Shape of docks and basins: These should be of shapes formed by straight

lines, as curved lines are not table for ships to stand alongside.

(I) Rectangular shape: The length and breadth could be adjusted to give the

maximum quay age.

Diamond shape: For the same perpendicular distance between the long sides; the

long sides could be conveniently extended.

(iii) Inclined pier type: It consists of a number of projecting piers into the basin or

dock.

A site on the sea coast is preferable to one up all as at Calcutta, where navigation

of the Hubei river is difficult especially as the river is congested with local traffic

proper piloting service is necessary for this purpose. River approaches to the

dock have to be maintained.

A -site on the estuary of a river, if sheltered, broad and free from storms is very

good (Southampton).

(4) Internal arrangement: Separate docks are usually required for different

kinds of cargo, as for example, oil should be dealt with separately, away from geneji

or food cargo. Flour acquires the smell of its surrounding and should not be

discharged near cargo, with strong odder like salted fish.

Other aspects:

(I) Availability of fresh water to replace leakage an fouled water from docks. In

inland ports, separate canal from the rivers will have to be drawn, for this purpose,

if alternate sources of supply are not available. In the case of sea coast docks, the

sea water could be used for cleaning and replenishing the dock.

(ii) Approaches must be sheltered and of sufficient depth In many cases, both on

the open sea coast or in inland docks, the approach channel has to be frequently

dredged.

DESIGN AND CONSTRUCTION OF BASIN DOCK WALLS:

(1) Design conditions: These walls are designed at gravity retaining wall sections.

They should satisfy the following conditions:

(I) Dock empty to withstand pressure of back-fill.

(ii) Dock full with back-fill removed.

(iii) Thickness at top should be sufficient to resist the shock of contact with

ships.

(iv) Dock walls have to carry additional concentrated loads like crane

foundations and capstans or bollard fixtures for mooring ships. Water front side

of dock wall must have fenders to protect the wall structure from impacts of

loaded ships.

(2)Design loads: Following are the loads of basin or ock walls which are shown in

figer.

(I) L.L - Live load

(ii) D.L. - Dead load

(iii) E.P. - Earth pressure

(iv)S.W.P. - Static water pressure

(v) Dy. W.P. - Dynamic water pressure

(vi)U.P. – uplift pressure

(vii)I.P. - Impact pressure due to ship.

(3)Effect of loads:

It may be noted that if water Accumulates at the back of the wall, the material will

exert; pressure corresponding to a fluid whose density is equal the density of the

mixture of silt and water. The pressure and the wall may cause the dock wall

either:

(i) The opposing force exerted by the earth in front of the toe

(ii) The strength of soil.

(iii) to sink at the toe due to increase in pressure above the bearing capacity

of the soil, or

(iv) to develop tension in the joint. It is also evident that there is no counter-

acting pressure exerted at right angles to the wall during its construction,

because the water is to be admitted after the completion of wall. Hence, the

wall will have to resist the earth pressure; at the back with its own dead

weight together with:

OTHER ASPECTS OF CONSTRUCTION DETAILS

(i) Basin walls have to be of much greater height the dock walls to allow for the

variation in water levels, due to tides. The floor of the basin will have to! Be

lowered to admit vessels at low water level.

(ii) 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.

(iii) The front face is generally straight or has a very slight batter for ships to

stand close to the walk The section usually adopted for walls is one with a

moderate thickness at top, stepping at the bac and vertical face. Sometimes the

back of walls ...is curved. The normal pressure on basin walls is greater than

dock walls due to the fluctuations of the tide level in a basin. Hence, the

basin walls are bigger sections as compared to those of dock walls

(iv) The front face is- given a granite fending surface or timber or steel fender to

protect the face q the wall from abrasion by ships.

(v) Dock walls are constructed of masonry, brickwork or concrete or a

combination of these material (with construction joints as in the case of concret

walls). Concrete walls are liable to abrasion an. hence, they are to be protected

by fenders or granite facing.

(vi) The walls must include tunnels and passages for hydraulic compressed air

and electric mains.

(vii) They must be provided with anchorages for bollards and crane

foundations.

(viii) During construction, it should be seen that the filling behind the wall is

composed of materials which are unaffected by water. They should be laid in

thin layers and well consolidated. The wall then have less chances to slip

forward.

(ix) Pipes should be laid in the wall during construction to drain off accumulated,

water from rear and they will have to be plugged, up before water is admitted

into the dock.

(x) Boring will have to be taken to ascertain the nature of soil on which the dock

walls will have' to rest. Generally, hard strata will be available at some

reasonable depth below the surface. The dock wall can then be placed on a

broad layer of foundation concrete. It must be seen that the intensity of bearing

pressure under the worst condition does not exceed the bearing pressure of the

soil on which the dock wall is resting.

DOCK ENTRANCES:

Vessels can enter docks either directly or through locks. In either case, gates are

provided for the dock entrances.

The types of gates used are:

(i) Wooden or iron gates

(ii) Caissons.

(1) Wooden or iron gates:

Wooden or iron gates are adopted for locks. The former type is described in

detail finder lock gates. An entrance to a dock takes less space .than a lock

and it requires only one pair of gates instead of two.

Also, the lock requires a special chamber. An entrance restricts the admission

of vessel to periods round about high tides only. On the other hand, a lock

enables vessels to enter the dock whenever required, provided approach

channel permits them to do so.

(2)Caissons:

Two kinds of caissons are employed

(i) Sliding caisson (ii) Ship caisson.

Brief description of each kind of caisson is given below

(i) Sliding caisson: It consists of a box shape steel structure stiffened

internally with proper bracing It is provided with steel keels sliding on smooth

granite floor. Instead of the keels, the caissons could be moved on rollers and

rails. The entrance is opened by hauling the caisson into a recess provided in

the side wall of the dock. The caisson also serve as a bridge across the dock

entrance.

(ii) Ship caisson: It resembles the outline d a ship in cross-section and is

constructed of ship with stiffeners at proper intervals. It is floated into position

and sunk into specially prepared groove in the dock sides and sill. The sinking

and raising of this caisson is done by ballasting and unballasting respectively.

This type does not require any gate recess or machinery for moving.

1. SIZES OF DOCK ENTRANCES:

The width of entrances depends on the beam of widest dock has to receive.

Modern ships have beam widths upto 30 m and to accommodate the largest

ship, the entrance will have to be sufficiently wide for this purpose, he beam of

a vessel means the width of vessel.

REPARING OF DOCKS

CLASSIFICATION OF REPAIRING FACILITIES:

(1) Repairing facilities in fixed form:

(i) Graving dry dock

(ii) Marine railway dry dock or slipway

(iii) Lift docks.

(2) Repairing facilities in movable form:

(i) Floating docks

(ii) Depositing docks

3. GRAVING DRY DOCK:

This stands still like a' grave of dead body hence it 's named graving dry dock. It

is an excavated chamber having, side walls, end wall, front opening with gate

and a solid floor. Side- walls are two in numbers constructed in form of 2 m

steps of concrete or masonry covered to be damaged by entry of water

and culverts at level to drain out unwanted liquids. The outer side provided with

batter or stepped to increase width at to make wall stable, against worst

combination. End wall may be square, circular, elliptical or trapezoidal in plan. It

is constructed solid without galleries side opening is covered by gate.

FACILITIES TO BE PROVIDED AT A GRAVI DRY DOCK:

(1) Lifting: Lifting and moving facilities are in of cranes of different capacities

2 tones to 50 ton Cranes put any materials in required location. and elevate

(2) Compressed air supply: This ensures work of pneumatic tools for

cutting, drilling, etc.

(3) Supply of salt water: Salt water supply is fill or flood the dock chamber

through culverts provide inside walls.

(4) Supply of fresh water: This water is for clean in the ship surface.

(5) Electrical power supply: This power sup-can run equipments like

welding set, capstans and pump

(6) Pulling equipment: These are well found electrical motors, known as

capstans, suitably on both side walls of dry dock.

gropes see in figer. When Capstan's motors are made on the axes on rotation

drags the ship inside dry dock, which is flooded upto water level of basin,

usually ship is to be dry docked when it is out of trim.

(7) Anchoring facilities in form of bollards: Bollards are very heavy iron

ingots in dumb-bell shapes l/3rd of which are founded on both

sides at an interval about 3 m to 5 m c/c. Ropes which are tied to

the ship, are round the bollard. Now by chance if one of the motors

is stopped the ship will

be dragged only on one which make the ship to go out of trim. The

ropes round the bollard will not permit the ship to go of trim.

(8) Supporting facilities:

(i) Supporting the ship from sides: Timber slides are strong, well-seasoned

timber rounds with metal cover at both ends. They are supplied through

smootli inclined sliding ways provided from floor to the inner side of dry dock.

Timber shores are supplied to dry dock chamber as and when required at

specific water levels. Timber shores when supplied to dock chamber they

float, the workers can collect them standing on steps of alter courses and set

them between corners of steps and ship surface to act as inclined struts

taking compression.

The side shores of steel are adjusted automatically from sides when they

come out of wall as horizontal cantilevers to be adjusted at projecting end to

touch the ship. The timber shores spacing cannot be exactly maintained as

they are adjusted by human labour, while spacing of steel shores can be

maintained.

(ii) Supporting the skip from bottom:

(a) At bottom centre through keel blocks.

(b) At bottom sides through bilge blocks or side blocks.

The graving dock, also known as a dry dock is a 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. There are figers show

the plan and an enlarged cross-section of a typical graving dock. It is still like a

grave hence is named as graving dock.

METHOD OF DRY DOCKING:

The ship enters the dock on adjusting the water level inside the dock to that of

outside, and the entrance gate is closed. The water inside the dock is now pumped

out by powerful pumps, the ship being kept vertical and central; by the shores

between the sides of ships and altar steps while slowly being lowered on to the keel

and bilge blocks on which it comes to rest. The main principle of operating a dry

dock is thus to admit a vessel into the chamber, close the gate and pump

out the water.

SIZE OF GRAVING DOCK:

The size of a dock depends on the size of the largest ship it has to dry dock.

Generally a long dry dock is built in such a way that by introducing intermediate

caissons, the dock can be divided into two graving docks of different lengths. Such

a construction permits the facility of accommodating two smaller vessels in place of

one big .vessel, when the necessity arises.

Dry docks to handle modern big ships have to be 300 m inlength, with

an entrance width of 25 m to 30 m. The ratios of length to breadth of

modern ocean liners are about 9.5 to 10.

One of the world's biggest dry dock is built in British 'Columbia. The Esquimalt dry

dock has a length of 350 m and breadth of 41 m. It is constructed of

concrete with granite altars. The pumping plant consists of 3 pumps , 270000

litres per minute capacity each, which empties th dock in 4 hours. This would

give an idea of the enormity of the dock size as well as its pumping

equipment.

FORCES ACTING ON A GRAVING DOCK:

The principal forces to which the dock is subjected are as follows:

(i) Weight of ship, resting along the centre-line of dock floor, when

dock is empty.

(ii) Weight of water on the floor when dock is flooded!

(iii) Upward pressure under the floor when it is being emptied.

(iv) Earth and hydrostatic pressures behind the side walls.

(v) Load imposed by the shores on the inside face of the side walls.

(vi) Surcharges on the side walls due to cranes and other heavy stationary

and moving appliances.

(vii)In addition to this, if there is a strong breeze blowing during dry

docking operations, the shores on the leeward side of the ship will be subjected

to wind stresses.

CONDITIONS FOR DESIGN OF GRAVING DOCK :

For purposes of design, the following conditions loading are to be investigated:

(1) Dock empty: The floor is subjected to heavy-uplift, which will be considerably

more than the weight of the floor itself. This unbalanced excess load is transmitted

to the side walls, by actual or virtual inverted arch action and being resisted by the

weight of the side wall and the horizontal pressures behind it. The weight of a

ship resting on the empty dock."' floor, adds concentrated loads along the centre-

line of the floor. Heavy reinforced floor sections may become necessary, if the

soil is soft or yielding, as intensity of this load may reach as high as 2600

kN to 3000 kN per tuning meter.

It is generally assumed that 5/8 of such loads are by the keel block and 3/8 equally

divided on the bilge blocks on either side, at the loaded sections.

(2) Dock filled with water: This condition imposes the greatest load on the

foundation. The horizontal pressures behind the side wall are more or less resisted

by the water fessure inside the dock. The inverted arch action of the floor will be

absent under this condition of loading and the full weight of the side wall less loss

due to buoyancy along with the surcharge loads, will have to be taken directly by

the foundation.

SCHEME OF CONSTRUCTING GRAVING DOCK:

Very careful thought has to be bestowed on the effects of horizontal earth and

hydrostatic pressures as well as uplift pressures during the construction of docks.

The sequence of Construction should be so manipulated as to ensure the stability of

the structure during construction. The following scheme in this. respect is

noteworthy:

(i) Site is partly excavated and portion marked a of the side wall is built.

(ii) The core b is excavated to lay the floor in short lengths and the outer

sections C1, C1 are laid, leaving the core in between. By so doing only small

lengths of the side wall are exposed to the lateral soil and hydrostatic

pressures. These pressures are being also sustained by the unexcavated

central core c of the floor and the completed sections of the floor C1, C1.

(iii) The flooring in the central section is placed after excavating the core c.

(iv) The upper portions of the side wall marked are at constructed.

(v) The back fill e is placed to complete the work

DESIGN OF GRAVING DOCK FLOOR:

The floor of the dry dock sustains loads both from above and below under

critical conditions like that the floor of locks, and floor thickness has to be

carefully designed. A simple numerical example will make this

aspect very clear.

Let us consider the concrete floor of a dry dock sustain 12 m of water over an

entrance width of 21 m Assuming a modulus of rupture of 1100 kN per m2 for

cement concrete, a floor thickness of nearly 6 m will become necessary, if the

foundation below the floor sinks and the concrete slab breaks, in consequence. But

actually such an extreme condition is rare. Then consider tHe same floor to

withstand the uplift pressure when the docks is empty, causing a reversal of

the original conditions Of course, this uplift pressure is to be taken up : by the

virtual inverted arch or actual constructed flat arch of the floor. In practice, it has

been found quite sufficient to design the floor thickness, to accommodate an

inverted arch of about 800 mm thickness and 14

rise, adding up to an actual floor

thickness of 5 m to satisfy all the above-mentioned conditions.

It would also be necessary to construct the side wall and the floor as independent

sections considering the divergent effect of the forces on them. It could.-be also

noticed that constructing the floor slab in sections. helps in its action as an inverted

flat arch to resist the upward pressure.

MARINE RAILWAY DRY DOCK:

Marine railway or slip dock or slipway is an inclined railway extending from the

shore well into the water as well as the foreshore, to enable a ship to be drawn up

to clear out of the water. The essential parts are a cradle which moves up and

down on inclined track and the track itself being supported on an

unyielding and firm foundation or pile foundation. The height is Minimum

300 m or twice the length of largest ship.

The cradle or platform is constructed of steel and provided with keel and

bilge blocks to receive the ship. The cradle is mounted on a system of

roller switch move on iron tracks carried by longitudinal timbers ,supported on

cross ties or beams bearing on piles or other firm foundations. Strong

cables are attached to the shore end of the cradle to haul the cradle.

Hauling is operated by strong mechanical winches built on shore. The

ways consist of heavy rails secured to longitudinal sleepers supported on cross ties

are laid at an inclination varying from 1 in 15 to 1 in 20. A locking device for the

safety pawls under the cradle is placed in the centre of the ways, to keep the cradle

from slipping down when the hauling cable breaks. For dry docking, the cradle is

moved down into deep water and the ship to be docked is towed over the cradle

and positioned to rest on keel and bilge blocks set on. the floor and moored to the

towers on either side of the cradle. The cradle slowly emerges above the high water

level, when hauled up the ways, permitting the ship to come to rest, on the cradle

floor as the cable reaches the normal docking position.

The use of this type of dock is no doubt economical but is limited to vessels of not

more than 50000 kN. It is due to the fact that long vessels with deep draft in the

ways would have to be drawn out a distance nearly twice the length of the vessel to

be docked. It also means : that the entire length of the ways would be over three to

four times the length of the vessel to be docked. In modern naval practice, this type

is yielding place to graving docks and floating docks which have become

popular.

SLIPWAYS:

(1) Components of slipways: This technique is used for the building of ships or for

repairs. A slipway consists of inclined path of timber or stone upon which a series of

rails are fixed and they run up from a sufficient depth of water to the required

height above the high water level. The lower end of the slip is tidal and open to

the water. The temporary dams are sometimes constructed to increase

the effective working length of the slipway.

(i) Flat footed rails: For the construction of slipways, 3 flat footed rails of

standard sections are used.

(ii) Crane track foundations: The main problem in slipway construction is

that the crane track foundation is partly in dry, partly between tides and

partly under water.

(iil) Cradle or carriages: The cradles or carriages are generally of the

following three types:

(a) Rigid type: These cradles are single long units and they can handle

vessels upto 10000 t. These cradles require longer slips.

(b) Semi-rigid type: These are comprised of a series of sections

closely coupled together with coupling system as simple as possible.

They require shorter slips as compared to the rigid type.

(c) Collapsible type: These cradles require shortest possible length

of slip and they reduce the expensive under water work to a

minimum. These cradles are in the form of a series of bogies

connected by chains.

(2) Traversing slipways: The slipways on which the ship after being pulled up to the

highest point can be I traversed sideways to other berths are known as the

traversing slipways. For this purpose, separate bogies are employed and the

arrangement of rails is made in such a way that the bogies, cradle and ship can be

traversed sideways to an adjacent berth. The ship is transferred by jacks to the

fixed berthing blocks clear of the cradle.

The bogies and cradle are then returned to the main slipway line and

the cradle is lowered to pick up another ship. This type of slipway is

useful where the number of ships coming for repairs is quite large.

LIFT DRY DOCK:

This is a substantially constructed platform capable of being lowered into and raised

from water. Raising and lowering are accomplished by means of hydraulic power

applied through cylinders supporting the ends of cross girders carrying the

platform.

As modern ships have considerably grown in tonnage and size, this ancient method

of dry docking had to be discontinued, giving place to more efficient and less

cumbersome types.

FLOATING TYPE DRY DOCK:

Floating dock may be defined as a floating vessel which can lift a ship out of water

and retain it above water by means of its own buoyancy It is a hollow structure of

steel or reinforced cement concrete consisting of 2 side walls and a floor, with the

ends open. To receive a ship, the structure is sunk to required depth

the buoyancy of the side walls and the side sections of the pontoon to carry the

concentrated load of the ship along the longitudinal central axis of the

floor.

(2) When unloaded and floating: The transverse strength should be sufficient to

support the weight of the side walls and other heavy machinery carried by on the

side walls, like pumping units, cranes, etc. When a ship is on the dock and

the dock commenced to rise, the water ballast from the side walls is unballasted

first. The sheath or skin of the side walls will thus be. exposed to the outside water

pressure and has to withstand this pressure. The maximum pressure will be

attained when the side wall is fully empty and the dock is still immersed and in the

process of rising. In most of the floating docks, this pressure is not allowed to

exceeds 6 m head of water. In order to get the full lifting effect, of floating dry dock

has to be fully unballasted which results in the dock structure taking all the

transverse bending strain. A correct. manipulation of the pumping out of ballast

will ensure avoidance of any undue or excessive train on the structure.

ADVANTAGES AND DISADVANTAGES OF FLOATING DRY DOCK:

(1) Advantages of floating dry dock:

(i) It is cheaper in initial and working costs.

(ii) It could be constructed in half the time it takes to construct a graving dock

of the same capacity.

(iii) It has the advantage of mobility and could be transferred from port to

port.

(iv) It could be trimmed to take a damaged arid lifting ship, which it could not

be possible to tow through the entrance of a graving dock.

(v) It has no elaborate entrance or gate arrangements,

(2) Disadvantages of floating dry dock:

(i) The durability or service life is appreciably less then The floating dock being

a steel structure constantly float in sea water could have a life of only about

50 years, like any other steel structure, whereas a well constructed

graving dock is practically indestructible.

(ii) Upkeep and maintenance are more since a floating dry dock itself is a

large floating vessel and needs dry docking, cleaning, painting, etc.

(iii) The manoeuvring and towing of a floating dry dock needs great skill and

care and in exposed situations it may not be possible to use it at all.

CONCLUSION

The historic importance of water transportation in making the cultural relations and

growth of civilization needs no discussion. It is the cheapest mode of

communication because the rail and road transport will require special tracks and

surfaces before they can be made use of the natural waterway is a gift of nature.

Also It leads to the overall development of commerce, industry and international

trade. It possesses high load carrying capacity.