4 inland water transportation 2

INLAND WATER

TRANSPORTATION

WITH PARTICULAR

REFERENCE TO RIVER NILE

(2)

October 13, 2009 1Dr. Adel Banawan

Ship Design-2

Resistance of push tows:

The resistance of pushed tows per ton displacement or

per ton dead weight is lower than single self-propelled

barges and tugs towing dumb barges, of the same

capacity and speed.


Ship Design-2

• Considering a push tow with barges raked at both

ends, Eddies are formed due to rakes at both end of

each barge.


Ship Design-2

• An increase in the resistance of barges due to

these eddies.

October 13, 2009Dr. Adel Banawan

Ship Design-24

• These gaps which are due to the raked ends, reduce

capacity of the convoy as these spaces could be used

for cargo and their buoyancy could be of one use or

another.


Ship Design-2

• To eliminate these two effects, the barges may be

made of square ends, hence when lashed together;

there will be no gap in between. In this case we have

two possibilities:


Ship Design-2

1- Each barge has one square end and one raked end.

When lashed together they will form one

hydro-dynamically single unit, with the gap in

between being eliminated.


Ship Design-2

If the convoy is formed of some groups of such

barges, it is called a semi-integrated flotilla


Ship Design-28

Each integrated group of barges must be loaded to

nearly the same draft; otherwise the resistance will be

unduly increased by the effect of the protruding part

of the barge with the deeper draft


Ship Design-29

2- All barges of the convoy are of box shape i.e., having

both end squares, and the most forward barge is to

have a box shape at its aft end and a raked shape at its

bow.


Ship Design-210

Obviously with such tows, all barges must nearly

have the same draft, otherwise ballasting may then be

necessary.


Ship Design-211

This system is termed the "Fully Integrated flotilla”


Ship Design-212

This system is considered to have the least resistance,

and the smallest fuel consumption per ton dead

weight compared to all other systems.


Ship Design-213

• In certain cases, the pusher is also to be made to draw

the same draft and can thus be integrated with the

convoy.

• In effect they will be a single hydrodynamic unit of a

larger size and length.


Ship Design-214

Construction of pushed barges:

• Pushed barges are of simple construction. In

particular the box ended barges of integrated and

semi-integrated barge systems are very simple to

construct and are adaptable to mass production and

prefabrication.


Ship Design-215

• The cost of such barges is very much reduced

compared to ordinary ship-shaped dumb barges. This

reduced constructional cost improves the economy of

the fleet.


Ship Design-216

• The type of cargo has a pronounced effect on the

design of barges. Barges designed and built to carry

dense cargo should be constructed with small volume

and high longitudinal strength.


Ship Design-217

• Interchangeability between various types of

commodities is of utmost importance to the owners

overall operations.


Ship Design-218

• River conditions determine the coaming height,

which is dependent upon the maximum wave height.


Ship Design-219

• Headlog and sternlog design is quite important in

regards to the resistance quality.


Ship Design-220

Consideration of resistance of inland water

transportation fleets:

• The resistance of these fleets increases over the

unbounded water resistance, due to shallow water or

the blockage effect.

• The increase of resistance due to shallow water is

appreciable particularly at higher speeds.


Ship Design-221

• At a water depth to draft ratio less than 2, the

resistance increases at a higher rate.

• The resistance increases with the reduction of the

underkeel clearance.

• A minimum clearance of 50cm is commonly used,

but this depends upon the speed.


Ship Design-222

• The ratio of length to breadth of the tow whether it is

a single unit or a pushed convoy will also affect the

resistance.

• A narrow long tow experiences less resistance than a

short board tow of the same size and advance speed.

• However the latter steers in a better way than the

former.


Ship Design-223

• The shape of the rake affects the resistance of a

particular barge. Spoon type rake proved to be more

favourable, though they cost slightly more in

construction.

• The radius connecting the rake to the barge bottom is

more importance than the rake slope itself.


Ship Design-224

Speed of inland water fleets

• The speed of the units, tows, or flotilla for inland

water transport depends on many factors.


Ship Design-225

1- Resistance

• The resistance can be assumed to increase as the

square of the speed because the resistance is mainly

frictional at such low speeds


Ship Design-226

• In water of a restricted depth the resistance increases

more rapidly with the speed because of the

introduction of wave-making resistance, until it

reaches a considerable high value near to the critical

speed.


Ship Design-227

2- Squat

• Squat is the increase in draft and change in trim due

to hydrodynamic effects caused by the motion of the

water round and under the ship at relatively higher

speeds.


Ship Design-228

• The squat increases as the speed increases and of

course, it also increases as the under keel clearance is

decreased.


Ship Design-229

• The condition of the waterway governs the maximum

permissible speed allowed to avoid unduly high

resistance and excessive squat, which may eventually

cause grounding. It also governs the maximum draft

to which units can be loaded.


Ship Design-230

• There are certain places where the depth of water is

rather small, it is usually more economical to load the

units to a draft which permits the units to pass such

places at very reduced speeds rather than loading the

units to smaller drafts in order to maintain a higher

speed.


Ship Design-231

3- current speed

• The current speed and the required transport speed

determine the minimum still water speed required.


Ship Design-232

4- type of commodity

• In cases where quick delivery is more important than

the reduced cost of transport, as in the case of

chemicals, perishable goods and finished products,

the speed can be made relatively high.


Ship Design-233

• With raw materials, gravel, clay, ….. etc., the speed is

normally low.

• It must be noted that, high speeds are best suited for

non-stop movements of a unit or a tow.


Ship Design-234

• The speed of inland water transport usually ranges

between 10.0-18.0 km./hr., in still water.

• A speed lower than about 8.0 km./hr. should be

avoided for safe maneuvering, unless special means

of steering is employed, such as the increase in the

rudder area.


Ship Design-235

Design ConsiderationSize of Unites, Overall Dimensions

• Each unit; barge, tug, pusher or self-propelled barge

has to be constructionally rigid. The ratio length /

depth governs the stiffness of the unit.


Ship Design-236

• The length of the unit is governed by the usable

length of the locks on route. To increase the

efficiency of the locks, the usable length of the lock

must be a multiple of the length of the unit (if the

units are made of standard length).


Ship Design-237

• Similarly the breadth of the lock must be multiple of

the breadth of the units plus some allowance.


Ship Design-238

• Hence for a developed inland water transport system

the length and breadth of the units should be

standardized and these standard dimensions are to be

chosen in connection with the dimensions of locks on

route.


Ship Design-239

• Standardization permits the mass production of units,

which in turn reduces constructional costs.

• It also permits the maximum efficiency of the locks

which affects the capacity of the waterway and the

time of the voyage leading to a reduction in the cost

of transportation.


Ship Design-240

Size of Pushed Convoy

• The maximum length and breadth of a pushed convoy

are also governed by the sharp bends on route. The

ratio of radius of curvature of the sharpest bend to

length of the convoy, of about 3.0 is considered

suitable.


Ship Design-241

• If the number of such bends is limited, it may be

found more economical to adopt a longer convoy

which could be broken into two parts and moving

each part through the bend at a time, after which the

two parts of the convoy can be brought together once

again.


Ship Design-242

• A pushed tow can either pass a lock complete at any

one time or it may be broken into parts, passing the

lock one at a time, then reassembled.


Ship Design-243

• It is clear then that the size of the lock does not

impose serious restrictions on the size of the convoy

provided that the lock is not too small compared to

the size of the convoy, and that the number of locks to

be passed is limited.


Ship Design-244

Power installed

• The power to be installed depends on the following:

1- The size of the tow whether a single barge, pusher

tug and dumb barges, or pusher barge and pushed

dumb barges.


Ship Design-245

2- The condition of the waterway and the required still

water speed When towing with or against the current.


Ship Design-246

• Steering causes a loss of the attained average speed

through water due to the repeated use of rudders.


Ship Design-247

• For upstream navigation the loss of power due to

rudder action is about 15.0% of the installed power,

and for downstream navigation the loss is about

20.0%.

• Hence a margin of about 25.0% of the power required

should be added to make up for the power lost in

steering.


Ship Design-248

Propulsion Machinery and Systems

• The propulsion machinery used in the River Nile is

invariably diesel engines, ranging in power from

150-300 H.P. at 1800-2400 r.p.m.


Ship Design-249

• The reverse reduction gearbox is usually 2.5 or 3.5:1

achieving propeller shaft rotation of about 600 - 700

rpm having an optimum propeller diameter of about

1.0 – 1.10m.


Ship Design-250

• The proposal to use gas engines should be considered

in future in order to make this mode of transport

virtually ideal from air pollution point of view.


Ship Design-251

• Screw propellers are invariably used either of the

conventional type or tunnelled propellers, Z-drive

systems are rarely used except in pusher tugs.


Ship Design-252

• It is the normal condition to have the single barges

propelled by a single screw arrangement, while twin

screw arrangements are only used in pusher tugs and

pusher barges.


Ship Design-253

4 inland water transportation 2

Documents