CSD is a stationary dredger equipped with a cutter device (cutter head) which excavate the soil before it is sucked up by the flow of the dredge pump(s). This type of dredger is capable to dredge all kind of material and is accurate due to their movement around the spud. The spoil is mostly hydraulically transported via pipeline, but some dredgers do have barge-loading facilities as well.

1. Prepared for IWAI
By K DIBYAJYOTI MOHANTA
M Tech : Dredging & Harbour Engineering
Indian Maritime University Visakhapatnam Campus
CUTTER SUCTION DREDGER

2. PRESENTATION AGENDA
Introduction to Dredging
Overview of the Dredger
Cutter Suction Dredger
CSD : Working Method
Equipments of a CSD
Factors Affecting Design of CSD
Design of Cutter Suction Dredger
Production Calculation of CSD
Latest Technological Advancement
Conclusion

3. INTRODUCTION TO DREDGING

4. OVERVIEW OF THE DREDGERS
DREDGER : A dredgers is a piece of equipment which can dig, transport and dump a certain
amount of under water laying soil in a certain time.
DREDGE PRODUCTION : The quantity of soil moved / dredged per unit of time is called
Production of a Dredge Plant.
Types of Dredger : According to the way to the Soil is excavated Dredgers are either
Mechanical or Hydraulic Type.
Mechanical Dredgers Hydraulic Dredger

5. CUTTER SUCTION DREDGER
CSD is a stationary dredger equipped with a cutter
device (cutter head) which excavate the soil before it is
sucked up by the flow of the dredge pump(s).
During operation the dredger moves around a spud pole
by pulling and slacking on the two fore sideline wires.
This type of dredger is capable to dredge all kind of
material and is accurate due to their movement around
the spud. The spoil is mostly hydraulically transported
via pipeline, but some dredgers do have barge-loading
facilities as well.
Sea going cutter suction dredgers have their own
propulsion, however this is only used during (de)
mobilisation.
Cutter power ranges from 50 kW up to 5000 kW,
depending on the type of soil to be cut.
Fig : Cutter Suction Dredger

6. per year
To Dredge, the ladder of the CSD has been
lowered under water, the dredge pump(s)
started and the cutter head set in motion.
The ladder is then moved down until it
touches the bottom, or until it reaches the
maximum depth.
The movement of the dredger round the
spud pole is initiated by slacking the
starboard anchor cable and pulling in the
port side anchor cable or reverse.
The thickness of the layer, which can be cut
in one swing, depends besides on the soil
conditions also on the size of the cutter
head.
At the end of the swing will either the ladder
be lowered and the dredger is swung in the
opposite direction or the dredger will make
a “step” forwards.
To ensure the efficiency of the side winches
the maximum swing angle is restricted to 45
degree.
CSD : WORKING METHOD
The soil or rock to be dredged is cut, dislodged, or
broken, by a powerful crown cutter. The
cutterhead may be electrically or hydraulically
driven. It encloses the suction intake pipework of
a centrifugal dredge pump.
The cutterhead is mounted at the extremity of a
fabricated steel structure, called a 'ladder', which
also supports the suction pipe.
The ladder is attached to the main hull by heavy
hinges which permit rotation in the vertical
plane. The ladder assembly is lowered and raised
by means of a hoisting winch controlled from the
bridge. Alternatively, on small dredgers, the
ladder movement may be controlled by hydraulic
cylinders.
The suction pipe includes a length of heavy
reinforced hose which imparts the flexibility
necessary to permit rotation. The Discharge Pipe
is located immediately outside the pump-room
bulkhead.
Fig : Swing Pattern of Cutter Suction Dredger

7. per year
Basic Design Criteria for Cutter Suction
Dredger can be summarised in to the
following Points.
1. Production Capacity
2. Dredging Depth
3. Width of Cut.
4. Type of Soil to be Dredged.
5. Transport Distance
6. Access to the Dredging Site
DESIGN CONSIDERATIONS FOR CSD

8. per year
Production Capacity of a CSD
The production capacity is determined by the mark demand with regard to the projects for which the
dredger can be used.
Design Production capacity of the CSD is related to the Relative Hardness of the Materials its going to
dredge. For example, 100 m /hr in a rock of 10 MPa. It is important that the production capacity is defined
m3 per week, hour or second. The smaller the unit of time chosen, the greater the production capacity.
The production capacity in the design-soil is known, this can be translated into a production to be cut by
the cutter head. This so called cutter production is considerably higher than the dredged production
because not all the material that has been cut enters the suction mouth. Often 20 – 30 % remains behind
as spillage. This must be taken into account when determining the production to be cut.
Production is usually highest in the middle of a cut. In the corners of the cut where manoeuvres are often
carried out with the ladder or spud carriage, the production is low or zero. This results in the fact that the
cutter production when expressed in m3/s is 20 –30% higher than the cutter production in m3/hr.

9. per year
Dredging Depth of a CSD
In the design of CSD both the maximum and the minimum dredging depths are
important. The usability of the dredger increases with increasing dredging
depth, while on the other hand it decreases as a result of the related smaller
minimum dredging depth.
• Maximum Dredging Depth :
- From construction point of view, itInfluences the Design of Main
Pontoon, Spud Pole, Ladder, Stability of the Dredger.
- From the point of view of production, the suction depth determines
whether an underwater pump is needed to obtain the required
production capacity. It is obvious that mounting an underwater pump
will increase the weight of the ladder.
- When no underwater pump , the diameter of the suction pipe and the
head of the pump must be increased and the concentration of the mixture
reduced in order to avoid creating vacuum. This may lead to the pumping
of low concentrations and thus much water, which is uneconomic.
• Minimum Dredging Depth :
The minimum dredging depth influences the min. draught of the pontoon, the
position of the cooling water inlet and the shape and construction of the cutter
ladder. The minimum dredging depth must be at least 1 m deeper than the
maximum draught of the vessel.
Note : When Dredging depth is less as
compared to the draft of the vessel, To
prevent dragging, the angle γ between
the underside of the ladder and the
horizontal must be at least 5 degree.

10. Width of Cut of a CSD
MINIMUM WIDTH OF CUT
•Minimum width of cut is taken to mean the
width that the dredger needs to dredge a
channel for itself in an area where the
surface of the ground is higher than the
water level.
•The minimum width of the cut is determined
by the line that meets the contour surface of
the cutter head at the front of the pontoon
or at the outer side of the side winch
sheaves.
•To reduce the minimum cutting width each
side of the front of the pontoon is often
chamfered
Fig : CSD with Chamfered Pontoon
MAXIMUM WIDTH OF CUT
• The distance between the spud and the cutter head determines the Maximum
Width of Cut.
• To ensure the efficiency of the side winches the maximum swing angle is
restricted to 45 degree ; so that the maximum width B = 2L*sin(45)+Dcutter, in
which L is the distance between the spud and the cutter head.
• The length L depends on the depth of the water and the position of the spud
pole.
Fig : Maximum width of Cut

11. Effects of Type of Soil, Transport Distance and Access to Dredging Site on CSD
TYPES OF SOIL
Type of Soil, influences the Design of Suction
and Discharge Pipelines, Selection of Dredge
Pump.
Ex- For same cutting power of a Cutter for a
CSD, Dredging Rocks will yield less Dredged
Materials as compared to Dredging Sand. In this
case to make the operation economical, dia of
the dredge pipelines can be made smaller to
achieve better concentration.
TRANSPORT DISTANCE
Discharge Length and Grain Size
Determines the required Pump Pressure
Determines the number of Dredge-Pumps required.
NOTE : The maximum allowable pump pressure depends on the quality of the
shaft sealing of the last pump. Often values exceeding 25 - 30- bar are not
permitted.
ACCESS TO DREDGING SITE
•Access to dredging site is not always easy.
•When the Site is confined by Land Mass, Its better to adopt the
MODULAR APPROACH in the Construction of the Dredger.
•When the LAD is a matter of concern, retractable propeller system
can be used in Self-Propelled Dredger.
•When bridges and other Infrastructure put restriction on the
navigation of the dredger due to less availability of vertical
clearance SPUD TILTING arrangement can be used.

12. EQUIPMENTS OF A CSD
Pontoon
Ladder
Cutter head + Dive system
Suction line
Support system + Winch
Spuds
Dredge Pumps + Discharge
system
Side Wires + Winches
Fig : Cutter Suction Dredger

13. Hull of a Cutter Suction Dredger
•The floating capacity of a stationary cutter suction dredger derives
from the pontoon that is constructed as a single unit (mono-hull
or mono-pontoon) for most large cutter suction dredgers and, for
demountable cutter suction dredgers, consists of several
pontoons.
•The pontoons beside the ladder well are often chamfered to form
trapezoids in order to limit the minimum width of cut.
•It is essential that there is a separate pump room: if the pumps
were located in the engine room a leakage or an error during
inspection of pumps might result in the flooding of the engine
room with a good chance of the dredger sinking.
•The pump room should be designed in such a way that, when
flooded, the dredger doesn’t sink.
•Furthermore the pipeline system must be designed in such a way
that the flooding of the pump room can be kept to a minimum.
Hull of a CSD

14. 1. Cutter Head
2. Onboard Pump
3. Submerged Pump
4. Onboard Rubber Hose / Bellow
5. Onboard Pipeline
6. Dredge Valve
7. Turning Gland
8. Floating Discharge Pipelines
Fig : CSD Dredge Pipe Line Arrangements

15. per year
Hydraulic Spud Carriage
Working Spud
Auxiliary Spud
Discharge Pipe
Ladder Pump
Suction Pipe
Cutter Head/Crown
Cutter Head Service Platform
Anchor Handling Boom
Onboard Service Crane
Control and Engine Room
Engine Exhaust Pipe
Ladder Handling Crane
Ladder Swinging Winches
Ladder
Fig : Cutter Suction Dredger Equipments

16. Equipments of CSD : CUTTER HEAD
Cutter Power, Cutter RPM, Cutter Dimension determines the Production that shall be
Excavated and Transported.
Cutter Power————————————> Ability to Cut the Soil
Cutter RPM --------------------------> Ability to form the Mix
Cutter Dimension -----------------> Facilitates Optimum Suction of Slurry
Cutter Power : Can be determined by from SPE (Specific Energy to Cut the designed Soil)
and/or Soil Cutting Theories. SPE is the Work needed to cut the Unit volume of Soil need to
be cut per unit time.
Pcutter = Q cutter * SPE
Production is usually highest in the middle of a cut. In the corners of the cut where
manoeuvres are often carried out with the ladder or spud carriage, the production is low or
zero. This results in the fact that the cutter production when expressed in m^3/Sec is 20 –30%
higher than the cutter production in m3/hr.

17. CUTTER HEAD cont.
Cutter Head Dimension depends on technical
specifications of the cutter suction dredger i.e.
Cutting Power and Side Winch Power, Cutter
RPM, Weight of the Ladder, and Type of Soil
to be Dredged.
With relatively high side winch forces and a
small cutter diameter, higher cutting forces
can be generated and thus harder soil can be
cut.
With the same cutter power in soft ground it is
necessary to use a bigger cutter diameter with
low side winch forces and a higher speed by
changing the gears of the side winch drive.

18. CUTTER HEAD For Different Types of Soil.
A. Hard Soil :
-> Cutter should withstand impact forces, must be heavy & robust.
-> Small in contour with replaceable teeth.
-> Should withstand extreme wear on both the Cutter Head, Teeth and
Adapter.
-> Good, accurate tooth positions.
-> The size of the fragments may not exceed the minimum passage pf
the Pump.
B. Non-Cohesive Soil :
->Good mixture formation required.
->Wide though flattened contour (little pumping action).
->Should able to withstand wear, especially of the cutting elements.
->Good, accurate tooth positions are needed.
C. Cohesive Soil :
-> The cutter head should not become blocked, so it is ample and round
in contour.
-> Open near the hub. Often with one less blade (thus 5 blades)
-> Good cutting properties in clay with small fragments.
-> Plain or serrated edges with many small teeth may be used.
NOTE : Though its good to use different Cutter for different Soils, in Market
there are Multipurpose Cutter Head that can dredge more than one type of
soil efficiently to redice the cost of the vessel.
Shape of Cutter Head for Different types of Soil

19. Elements of a CUTTER HEAD
The hub by which the cutter head is mounted via an ‘Acme” or three threaded
screw onto the cutter shaft. The distance between the underside of the ring and
the underside of the hub is termed the set height.
• The cutter arms or blades, usually 5 or 6. The number is related to the
required strength and/or space between the arms. The cutter arms form a
screw shape and link the ring to the hub.
• Edges (knives) or Replaceable Teeth or Chisels are mounted on the cutter
arms. The tooth is attached by means of a locking pin to an adapter that is
fastened to one of the blades. In hard soil a six bladed cutter head is often
used with teeth on the even blades that are offset in relation to those on the
uneven blades. This is termed ‘staggered mounting’.
• Skirt : The passage through the cutter head increases towards the ring. This
may cause blockages in the pump if fragments that are too large for the pump
can be taken up. The passage through the cutter head is sometimes reduced
by the addition of skirts, which are welded onto the blades to extend the
cutter arms.The passage can also be reduced by the welding of plates
perpendicular to the blades.
Fig : Elements of a CUTTER HEAD
Fig : Elements of a CUTTER HEAD

20. Types of CUTTER HEAD
A. Plain Blade Cutters :
Should be used only in soft materials, such as silts, fine sands and loose clays.
Blade edges are normally replaceable.
By increasing the number of blades the gap between the blades is reduced.
This restricts the size of solid which can pass and thus useful when dredging in areas
which contain debris or large stones.
B. Serrated Blade Cutters :
Should be used in consolidated materials such as firm to stiff clays, dense sands or
occasionally in very weak or highly weathered rocks. The blade edges can be replaced
when worn.
C. Rock Cutters
Rock cutters are of heavy construction with a generous blade section. The shape of the
blades is designed to maintain the maximum number of teeth in contact with the face
regard- less of dredging depth.
Blades have integral adaptors to which may be fitted different patterns of replaceable
teeth.
Teeth are formed from highly wear-resistant alloy steel and are attached by means of a
single sprung pin which allows a tooth to be changed in a few minutes.
D. Multipurpose Cutters :
Can be equipped with different types of teeth depending upon the site characteristics
and can cut more than one or combination of Soil Types. Cost effective from initial
investment point of view.
E. Special Purpose Cutters :
Designed by Dredge Manufacturer as demands of dredge contractor and specific
dredging site and to meet the cost requirements of the owner.
Plain Blade Cutter Serrated Blade Cutter
Rock Cutter
Specially Designed Cutter
ID : Lancelot (Royal IHC )
Multi Purpose Cutter

21. CUTTER HEAD DRIVE
• The cutter head drive is mounted on the ladder either near the hinge side (the
trunnion) or close to the cutter head.
•Cutter Head Drive @ Near to Ladder Hinge :
The cutter head drive is mounted near the hinge the shaft must be both long and heavy
because of the high torque. This long shaft needs several ladder bearings.
• Cutter Head Drive @ Near to Cutter :
Head when the drive is mounted close to the cutter head there is more freedom to
adapt the direction of the cutter head axle to the required angle, especially when
dredging in shallow water.
•Cutter Head Drive may be of Hydraulic Driven or Electric Driven. Criteria to select the
Type of Drive is “expected relation between the average load and the peak load. “
•Electric Drives: Are especially suitable because they can take overloading up to
150% without stalling. This is possible because of the considerable rotation energy of
the rapidly turning electric motor.
•Hydraulic Drives : But owing to the dynamic process in Heavy Dredging Operation,
gearboxes for cutter drives have to resist heavier loads than gearboxes for the all
drives on board of the dredge. The dynamic cutting process and as consequence the
torsion vibrations cause remarkable increase of the torque. In this case Hydraulic
Driven Cutter Head is recommended.

22. WINCH DRIVE, LADDER DRIVE, PUMP DRIVE
• WINCH DRIVE : Winch Drives may be
electric or hydraulic. Standardisation
and Price determines whether its
electric or hydraulic.
• LADDER DRIVE : Drives must be easy to
regulate and must not slip when the
ladder drive is not activated.To prevent
this slipping the winch must be
equipped with a break or ratchet.
• PUMP DRIVE : Underwater Pump are
mostly electric driven. Diesel Drives are
more suitable for Discharge Pump and
Booster Stations. Speed control is less
important for jet pumps than for dredge
pumps, because of the almost fixed
layout of the pipeline and the constant
fluid density.
Ladder Drive
Winch Drive
Pump Drive

23. ANCHOR BOOM
• The anchor booms are placed on the bow pontoons at the point where the chamfering starts and
fastened to the deck by a pivoting construction. Each anchor boom is fastened by one or more wires to
a frame or, as if often seen, to the ladder gantry.
• The anchor boom can turn on its pivoting construction by means of the anchor wires which are fixed to
the top of the anchor boom and which run via a series of sheaves to the anchor winches.
• The anchor wire, which is used to pull up the anchor, runs from the anchor to the top of the anchor
boom via the anchor boom downward and then via a set of sheaves to the anchor winch.
Fig : Anchor Boom

24. SPUD SYSTEM
• The spuds are fastened via spud doors to the spud carriage
or the pontoon.
Because the spuds are loaded on a bending moment the
wall thickness increases with the stress level.
• To obtain a good penetration into the soil, the lower ends
of the spuds are pointed. In hard soil the spud is often
dropped in free fall and needs therefore a massive point.
• In soft ground, on the other hand, the spuds are set down
to prevent them from sagging too far into the ground.
• During transport the spuds must be carried horizontally, so
most cutter suction dredgers have special equipment for
this purpose known as SPUD TILTING ARRANGEMENT.
• Spuds are hoisted by simple wire or pulley or by hydraulic
system. Though first two are relatively simple, from overall
operation and maintenance sling attached with hydraulic is
better, thus mostly used.
Tilted Spuds in a Model CSD Model
Spuds lying in Shipyard
Hydraulic Spud
Hoisting System

25. ADVANCEMENT MECHANISM OF CUTTER SUCTION DREDGER
•The choice of the spud system plays an
important part in the design of the cutter
suction dredger. The spud system influences
not only the layout of the pontoon, but also
the efficiency of the cutter suction dredger.
•There are six types of mechanisms, out of
which the most frequently used systems are
the spud carriage system and walking spud
system.
• The Spud Carriage System
• The Fixed Spud System
• The Spud Door System
• The Walking Spud System
• The Rotor Spud System
• The Christmas Tree System
Effectiveness of Spud Carriage System vs Fixed Spud System

26. Spud Carriage System
• With the spud carriage system the work spud is placed in a carriage
which, with the aid of a hydraulic cylinder, can travel over several metres
(4 - 6 m) in longitudinal direction in a well at the stern of the dredger.
• The carriage is generally positioned in the centre of the dredger and is
support by four wheels on rails for the vertical forces and by guide rollers
or bearing strips for the lateral forces.The cylinder is a double acting
hydraulic ram.
• A second spud, the auxiliary spud is mounted at the stern of the pontoon,
which is used to move the carriage back to its start position.
• The initiation of a new cut is obtained by moving the spud carriage one
step forwards. After stepping, the cutter head describes concentric circles
until the spud carriage reaches the end of the stroke of the hydraulic
cylinder.
• The return of the carriage usually takes place in the middle of a cut in the
following sequence of actions.The auxiliary spud is lowered and the
work spud is lifted, the carriage is moved back and then the spuds again
changed.
• After each single swing the dredge master is “ free either to step
forwards or to lower the ladder till the final is reached.
Images of Spud Carriage System
Swing Pattern in Spud Carriage System

27. Fixed Spud System
When using fixed spuds both the work spud and the auxiliary spud are in fixed
positions on the stern of the pontoon at equal distance from the centre line of
the dredger .
The step or start of the cut is now initiated by letting the dredger make an
angle from the centre line, then lowering the auxiliary spud and lifting the
work spud.
The dredger is then swung into a symmetrical position with regard to the
centre line where both spuds are changed again.
After each single swing the ladder is lowered till the final depth is reached.
It will be clear that stepping with fixed spuds takes considerably longer than
with a spud carriage, due to the down time of the swing movements.
Swing Pattern in Fixed Spud System
Fixed Spud System

28. Spud Door System
For small dredger a cheaper system than the spud
carriage is developed by IHC-Holland; the so called
“Spud Door” In A heavily constructed door, pivoting
around the auxiliary spud, is placed the working spud.
The dredge pattern is the same as for the spud-carriage
system, however spuds have to be changed more
frequently and the accuracy is less because the working
spud stays not exactly in the centerline of the dredger.
The system is much cheaper than the spud carriage
system.
Spud Door System

29. Walking Spud System
✦The walking spud system is similar to the
spud carriage system with regard to the
movement of the cutter head during
swinging and stepping.
✦The working spud is not in a carriage but
swivels round a horizontal axis. The step is
now taken by allowing the spud to tilt to the
requisite angle.
✦Disadvantage :
• The maximum step depends on the depth
of the water and so walking spuds are
difficult to use in shallow water.
• It is very little or not at all cheaper than a
spud carriage. The number of spud
movements is considerably larger.
Walking Spud System

30. Rotor Spud System
✦During dredging the midpoint of the rotor remains in the
centreline of the cut, so the dredger turns round the rotor.
Stepping is accomplished by lifting the rear spud and turning
the rotor until the rear spud becomes the front spud.
✦Using this system the dredger makes a pattern of concentric
circles. The advantage of this type of system is that when
stepping, only one spud has to be raised and lowered.
✦Advantages :
•Actual dredging time in relation to total time per spud cycle,
the spud wagon is the best.
•The number of spud changes per metre of progress is
minimal.
✦Disadvantage :
•It is very expensive.
•The spuds cannot be placed horizontally.
Rotor Spud System

31. Christmas Tree System
• There are situations in which anchoring by means of spuds is not possible. Such a situation
arises when working at sea if the forces that waves or swell can exert on the spuds are too
large. In this case strategy of the Dredge Contractor is Christmas Tree.
• A construction with wire leads, is mounted in one of the auxiliary spud carriages. With this
the anchor wires meet at one point under the under the hull. However, in order to keep the
cutter head well into the face throughout the entire swing the laterally directed anchors of
the Christmas tree must stand well forward. With the disadvantage that they must be
moved frequently. For this reason a bow anchor is often used.
✦ Advantages:
•Large and considerably bigger cutting width can be achieved.Good For Sand-mining Cutter
Suction Dredger
✦ Disadvantages :
• At least three anchors must be moved.
• The freedom of movement when working on anchors is so great that it is almost
impossible to dredge accurately.
• This is equally true for dredging in hard soil. A star system is needed for this.
Christmas Tree System

32. PRODUCTION CYCLE OF A CUTTER SUCTION DREDGER
✦ Production of a CSD depends upon the following factors :
• Pump Hydraulic Head
• Applied Power available for Pumping
• Ability of the Cutter to Break-down the Materials
• The Rate at which the Dredger can be advanced into the face.
✦ Factors can be illustrated as follows.
1. Traverse face
The speed of traverse is governed by the characteristics of the material to be dredged, the depth of
cut, the pumping distance and the dredging depth.These govern hauling winch speed and cutter
revolutions.
2. Number of cuts
The number of cuts across the face to produce a required level is dependent on the thickness of
material to be removed and the depth of each cut.The depth of each cut is governed by the
characteristics of material to be dredged. Usually one final cleaning cut is required.
3.Advance into face
Entirely dependent on the spud system employed.The time occupied will be a minimum when
using a spud carriage, or tilting spud, and maximum for fixed spuds.
NOTE : Daily production is the product of the average hourly production and the effective work- ing
hours per day.The effective working hours will be the total available hours that the dredger is
manned, less any lost time.
For a well-managed dredger, under average site conditions, the lost production time may be in the
range, 20 to 30 per cent of the theoretically available working time.
Fig : Production Cycle of a CSD

33. Fig : Dredging Cycle of a CSD
DREDGING CYCLE OF A CUTTER SUCTION DREDGER

34. DREDGE PUMP
★ Dredge Pump is an instrument with which the energy in a drive system can be converted into
transport energy and used to move a mixture of Soil and Water.
★ The most important properties are :
Wear Resistance, Effective Sealing, Robustness, Simplicity,Acceptably Low Cost, High Efficiency,
Flat Efficiency Curve, Low NPSH, Large Manometric Head, Large Diameter for Passages.
★ Constructional Features that a Dredge Pump should Possess :
❖ Size of Passage is important as High Efficiency and High Output can be negated by downtime
caused by blockage of the Impeller.
❖ Wearing Plate should be inexpensive to replace.
❖ Large wall thickness of components which are subjected to wear thus ensuring long life. Life of
the pump housing can be increased by installing a doubled wall unit. Because it is pressure -
compensated and encased in an outer housing can be made from more wear-resistent & brittle
material without fear of the vessel being flooded in the event of the inner housing fracturing.
❖ Simple, inexpensive construction. Easy to dismantle and reassemble.
❖ A flat efficiency curve, signifying high efficiency over wide operating range.
❖ Excellent cavitation characteristics.
Dreddge Pump
DREDGE PUMP

35. 35
TRANSPORTATION OF DREDGED MATERIALS THROUGH DREDGE PUMP

36. DETERMINATION OF OPTIMUM FLOW RATE
36Fig : Determination of Optimum Flow Rate using Slurry Transportation Fundamentals

37. DREDGE PIPELINES IN A CUTTER SUCTION DREDGER
The pipeline will have an important effect on
both the performance and operational
efficiency of the cutter suction dredger.
The diameter of the pipeline will directly
influence the efficiency of the hydraulic
transport process. If the diameter is too small,
head losses due to friction may be
unacceptably high.
If the diameter is too great, the flow velocity
may be inadequate to maintain the solids in
motion, or the power requirement may
become excessive.
Typical mixture velocities necessary to
transport various types of material without
undue risk of pipeline blockage are given
below. Fig. : Dredge Pipelines with a CSD

38. TRANSPORT VELOCITIES NECESSARY FOR VARIOUS DREDGED MATERIALS
MATERIAL TYPE SIZE VELOCITY RANGE in m/sec
SILT 0.002 to 0.063 mm 2.0 - 3.0
FINE SAND 0.12 mm to 0.25 mm 3.0-4.0
MEDIUM SAND 0.25 mm to 0.5 mm 3.5-4.5
SHELL 3.5-4.5
VERY SOFT CLAYS 0.00381 mm 4.0-5.0
COARSE SAND 0.50 mm to 1 mm 4.0-5.0
SAND WITH FINE GRAVEL 4.00 mm to 8 mm 4.5-5.0
SAND WITH MEDIUM GRAVEL 8 mm to 16 mm 4.5-5.5
STIFF CLAYS 0.0042 mm 4.5-5.5
SAND WITH COARSE GRAVEL 16 to 32 mm 5.0-5.5
SAND,GRAVEL, COBBLES 64 mm to 256 mm & Larger 5.5-6.5

39. LIMITATIONS OF A CUTTER SUCTION DREDGER
✦The limits on where the cutter suction dredger can operate
and what it can achieve will vary according to the size and
characteristics of the particular dredger, but an indication
of the extreme limits which will apply to economic
operation is given below.
✦These limits apply respectively to the smallest (minimum)
and largest (maximum) cutter suction dredgers in common
use.
✦When dredging in enclosed waters, for instance lakes and
ponds, where the rate of water inflow is less than the
pumping capacity of the dredger, it should be borne in
mind that the water level will fall, with potential adverse
operational and environmental consequences. Even the
smallest dredger may remove water at a rate of 300 cubic
metres per hour.
Limitations of CSD
Sl No Description Limit
1 Min Water Depth 0.75 m
2 Max Water Depth 35 m
3 Max Cut Width 175 m
4 Max Wave Height 2 m
5 Max Swell 1 m
6 Max Cross Current 2 knots
7 Max Ice Thickness 200 mm
8 Max Particle Size 500 mm
9
Max Comp. Strength (Rock
Dredging)
50 MPa

40. REFERENCES
-R N BRAY : DREDGING, A HANDBOOK FOR ENGINEERS
-JOHN B HERBICH : HAND BOOK OF DREDGING ENGINEERING
-LECTURE NOTES TU DELFT
-LECTURE NOTES INDIAN MARITIME UNIVERSITY
-LECTURE NOTES IIT-NPTEL
-DREDGING CORPORATION OF INDIA OPERATION MANUAL
-IMAGE COURTSEY : ROYAL IHC, VOSTA LMG, DAMEN, JAN DE NUL, VAN
OORD, DCI, IWAI etc