factors effecting performance

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Chapter title

FACTORS AFFECTING PERFORMANCE

By Bert van Gent

Dredging and Marine Contractors

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Dredging…?

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Double production…!


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Breakdown of the dredging process

Overview of dredgers

• Cutter suction dredger

• Trailing suction hopper dredger

• Backhoe dredger

• Grab dredger

• Other equipment

• Environmental dredgers

Equipment


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1. Loosening the material (and/or dislodging)

2. Picking up the loosened material

3. Transport

• through the primary dredger

• further transport

4. Disposal of the material

• under water

• on shore

Breakdown of the Dredging Process


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• Hydraulic (erosion, discharge pipe, etc.)

• Mechanical (cutter, conveyor belt, etc.)

Remark

The different sub-processes may require different types of

dredging equipment

Means to realise the partial processes


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1. Hydraulic/mechanical dredgers (CSD)

2. Hydraulic dredgers (TSHD)

3. Mechanical dredgers (Backhoe, Grab)

4. Environmental dredgers

Overview of dredgers


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Cutter Suction Dredger (CSD)

Hydraulic/Mechanical Dredgers


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Cutter Suction Dredgers

Mid-size, 600-1500 kW

Small < 600 kW

Large, 1500-3000 kW


Cutter power

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Mega, 5500-7500 kW Heavy Duty, 3000-5500 kW

Cutter power



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• Main characteristics

• Most important parts of the dredger

• Working principle

• Production limiting factors

• Some characteristic figures



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Main characteristics

• Nearly all kinds of soils (sand, clay, rock)

• Stationary dredger:

− vulnerable to shipping

− sensitive to wave conditions

• Some are self-propelled for mobilisation



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Cutter Suction Dredgers - Parts


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Most important parts, machinery

• Cutter head and cutter drive

• Dredge pump(s)

• (Side-) Winches and sheaves for the side

wires for swinging



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Working principle

• Cutter disintegrates or dislodges the material

mechanically by rotating cutter head

• Material sucked up and transported through pipeline

by use of centrifugal dredge pumps

• Pontoon movement by:

- swinging around working spud

- progress by successive steps (stepping)

and spuds (spudding)



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CSD WORK METHOD (1)

Swing

to SB


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Stop at SB,

Push dredger

forward

CSD WORK METHOD (2)

Dredging and Marine Contractors Dredging and Marine Contractors

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Start swing

to PS

CSD WORK METHOD (3)


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Continue

swing

to PS

CSD WORK METHOD (4)


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Stop at PS,

Push dredger

forward

CSD WORK METHOD (5)


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Start swing to SB

CSD WORK METHOD (6)


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Stop in

Centre Line

CSD WORK METHOD (7)


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Aux. spud

down

CSD WORK METHOD (8)


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Main spud

up

CSD WORK METHOD (9)


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Main spud

forward

CSD WORK METHOD (10)


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Main spud

down



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Aux. spud

up



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Start

swing

to SB


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Continue

swing

to SB


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Process topics

• Over-cutting versus under-cutting

• Spill

• Cutter heads

• Anchors

Cutter Suction Dredger


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spillage

(cutting deeper than design level)

undercutting overcutting



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Cutter head

• Back ring - arms - hub

• Blades - teeth: chisels / pick points

• Various shapes

Cutter with chisels



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Sand/clay cutter head


Rock cutter head


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• Anchors

Depending on soil type

Flipper Delta

Stevshark



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• Anchors

Anchor islands



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Production limiting factors

• Soil characteristics

• Available power on cutter

• Side winches (max. power and velocity)

• Thickness and width of the layer to be dredged

• Dredging depth (ladder angle, spuds, cavitation)

• Pumping distance (pump- and pump drive characteristics)

• Shipping

• Waves and currents

• Dirt and debris



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cutter suction dredger small mid-size large

dimensions 65 * 10 * 2 m 70 * 16 * 4 m 120 * 20 * 5 m

(L*W*Dr)

total power < 3,000 kW < 9,000 kW < 13,000 kW

cutter power < 600 kW < 1,500 kW < 3,000 kW

max. swing speed 19 m / min 32 m / min 32 m / min

max. dredging depth 15-20 m 25 m 25 - 30 m

discharge diameter 0.35 - 0.70 m 0.65 - 0.85 m 0.75 - 0.85 m

Characteristic Figures



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cutter suction dredger heavy duty mega

dimensions 125 * 22 * 5 m 140 * 24 * 6.5 m

(L*W*Dr)

total power < 23,000 kW < 28,000 kW

cutter power < 5,500 kW < 7,000 kW

max. swing speed 32 m / min 32 m / min

max. dredging depth 25 - 35 m 30 - 35 m

discharge diameter 0.80 - 0.90 m 0.90 - 1.00 m




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Suction dredgers

• Trailing Suction Hopper Dredger (TSHD)

• Plain suction dredger

• Barge unloading dredger

• Water Injection Dredger (WID)

Hydraulic Dredgers


ing and Marine Contractors

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Trailing Suction Hopper Dredger


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Mid-Size 8,800 m3

Large 13,500 m3

Small, 4000 m3



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Jumbo 18,000 – 22,000m3

Mega 37,000 m3



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• Most important parts of the dredger

• Process description





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• Free sailing

• Self-propelled

• Self-loading when trailing

• Self-unloading or -discharging

• Seagoing or inland waterway vessel

• All soils (also weak rock!)

• Relatively insensitive for waves

• Not vulnerable for shipping



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bow-coupling for pumping ashore or rainbowing

suction pipe hopper

service crane

pump room

propulsion

engine room

swell compensator

wheel house

draghead

- 70m



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Most important parts

• Dragheads

• Dredge pump(s)

• Hopper, loading and unloading system



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Dredging cycle

• Loading at the dredging- or sand borrow area

• Sailing (loaded) to the unloading area

• Unloading (dumping or pumping)

• Sailing (empty) to the dredging area

TSHD Process Description


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Excavation (Erosion & Cutting)


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Suction



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Loading Loading (overflow)



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Longitudinal section

Top view hopper

Loading: Basic Principle



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Top view hopper

Full Load: Basic Principle

Longitudinal section



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Text (full)

Hopper loading (mud)


Total Volume [m3]

Draught [m] (=tons)

Max.

draught

Max. volume

Mud [m3]

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Text (full)

Hopper loading (sand)


Draught [m] (=tons) Max.

draught

Overflow losses

Sand [m3]

Total Volume [m3]

Max.`volume

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Sailing loaded



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Discharge



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Rainbowing

Hopper Self-discharge: rainbow


DDredging and Marine Contractors

ng and Marine Contractors

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Hopper Self-discharge: Pump ashore



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Text (full)



Hopper Self-discharge: system

Dredge pump

Jets Jets

Water

Sand

Jets

Water inlet Discharge

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Text (full)



Jets Jets

Dredge pump

Jets

Water inlet


Discharge

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Text (full)



Jets


Dredge pump

Jets Jets



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Text (full)



Jets Jets


Dredge pump

Jets



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Sailing empty



start overflow

DRAUGHT (m)

start

dredging

stop

loading

sailing

loaded

emptying hopper

sailing

empty

TIME IN MINUTES

Cycle-time per trip

next

trip

TSHD Load Graph (emptying by bottom door disposal)

VOLUME SAND (m3)

TOTAL LOAD (ton)


start overflow

DRAUGHT (m)

start

dredging

stop

loading

sailing

loaded

unloading

hopper

sailing

empty

TIME IN MINUTES

Cycle-time per trip

next trip

VOLUME SAND (m3)

TSHD Load Graph (discharging to shore)


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Process related topics

• The hull

• The hopper

• Dragheads, suction pipes and belongings

• Centrifugal pumps



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The hull

• Sailing characteristics

• Resistance

• Small keel clearance

• Maximum carrying capacity versus draft, length and width

• Strength

• Stability



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The hopper

• Carrying capacity

• Volume

• Weight

• Filling system

• Overflow system

• Bottom door disposal system

• Self-discharge system



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Hopper: carrying capacity

Restriction by volume (full hopper)

Restriction by weight (max. draught)

Low density soils

e.g.: Mud - 1.2 ton/m3

5,000 x 1.2 = 6,000 ton

High density soils

e.g.: Sand - 2.0 ton/m3

3,500 x 2.0 = 7,000 ton

HOPPER

HULL

MUD

5,000 m3

6,000 ton

HOPPER

HULL

SAND

3,500 m3

7,000 ton


Overflow System

Conical bottom-valves

Bottom-doors

Hopper: loading & dumping facilities


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Dragheads

DDredging and Marine Contractors

ing and Marine Contractors

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Sand Draghead


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Different dragheads


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Suction Pipe


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Workability – Weather Delay

DrDredging and Marine Contractors

edging and Marine Contractors

Swell

Compensator

Draghead Winch

Pressure

Jar

Seabottom

Swell Compensator

Oil

Draghead


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Centrifugal Pumps

Hardware

• Types & sizes

• Basic parts

inboard pump under water pump


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Working principle

• Energy Distribution

• Propulsion

• Pumps

• Boardnet

• Centrifugal pump

Centrifugal Pumps


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Density & velocity meter

Engine-room with 2 pumps in line

Centrifugal Pumps


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• Soil characteristics

• Available propulsion power

• Drag head size and weight

• Keel clearance when loaded

• Dredging depth

• Pumping distance (pump- and pump drive characteristics)


• Dirt and debris

Production may vary a lot due to these factors



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Limiting factors

A drag head grid damaged by boulders


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Limiting factors

Dirt and debris


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trailing suction small mid-size large

hopper dredger

dimensions 55*10*4 m 90*18*7 m 130*23*9 m

(L*W*Dr)

max. dredging 10-35 m 25-55 m 25-75 mdepth

hopper capacity <4,000 m3 <8,000 m3 <15,000 m3

sailing speed 8 knots 12 knots 14 knots

propulsion power 400 kW 3,500 kW 8,000 kW

diam. suction-pipe 0.35-0.9 m 0.80 m 0.90-1.00 m

Trailing Suction Hopper Dredger Characteristic Figures


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trailing suction jumbo mega

hopper dredger

dimensions 180*32*13 m 225 x 38 x 12 – 15.5 m

(L*W*Dr)

max. dredging 50-120 m 55 - 155 mdepth

hopper capacity <30,000 m3 30,000 - 46,000 m3

sailing speed 17 knots 16 - 18 knots

propulsion power

(while dredging) 18,000 kW 26,000 kW

diam. suction-pipe 1.20 m 1.2 - 1.4 m

Trailing Suction Hopper Dredger Characteristic Figures


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Suction Dredgers

• Plain Suction Dredger

• Barge unloading dredger

• Water Injection Dredger (WID)

Other Hydraulic Dredgers


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• Suction of free running material (sand)

• Jet water for dislodging and fluidising material

• Deep suction pit necessary

• Stationary dredger, not swinging, only intermittently moving forward

Plain suction dredger


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Barge Unloading Dredger

• Unloading of barges by suction

• Jets for dislodging and fluidising

• Barge to be shifted alongside the dredger during suction


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Water Injection Dredger

• Injection of water into bottom

• Low pressure and high capacity

• Fine sand and silt

• Movement of material due to gravity forces (density current)


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Backhoe Dredger


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Backhoe Dredger

Mega backhoe Simson, 3460 kW


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• Typical parts

• Dredging cycle



Backhoe or Hydraulic Excavator


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• Normal backhoe/front-shovel on pontoon or

• Specially built pontoon (with spuds) with backhoe on rotating table

• Dredged material is loaded into barges

• Reasonable cutting force can be generated

• Suitable for:

• “Non-rock” type soils with stones

• Blasted rock

• Precision dredging

Backhoe


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Dredging blasted rock

Backhoe


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Bucket

Stick Boom

Backhoe - parts

Spud


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• Different types and sizes to be fitted:

• Sticks

• Buckets

• Booms

• Positioning with spuds

Backhoe


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Dredging cycle

• Lowering bucket

• Filling bucket by cutting and tilting

• Hoisting bucket

• Turning crane towards barge

• Emptying bucket into barge

• Turning back

Backhoe


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overlap Nett dredging width

Centre line

Reach

Barge

Working Method Backhoe

Preferred working direction:

backwards

=> Higher production

=> Less spill

But…

Forward dredging is also possible


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• Work method

• Excavation force at large depth

• Slope dredging (bucket positioning)

• Precision dredging along quay-walls

• Soil and obstructions

• Hard material (no rock)

• Big boulders

• Removal of debris or vegetation

• Workability

• Waves

• Shipping

Production Limiting Factors


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Backhoe Small Medium Large Mega

Length m1

30 45 50 65

Draught m1

1.5 2.0 2.5 3.5

Dredging Depth m1

10-15 15 - 20 20 - 30 20 - 30

Bucket size m3

1 - 3 2 - 8 5 - 20 15-40

Power Installed kW 500 < 1,000 < 2,000 < 4200

Backhoe Characteristic Figures


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Backhoe

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Grab Dredger


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• Dredging characteristics

• Typical parts

• Dredging cycle



Grab Dredger


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• Can also be used for construction works (shore & bank protection)

• Normal grab-crane on pontoon

OR

• Specially built pontoon (with spuds) with fixed grab-crane on rotating table

• Small grab dredgers for difficult accessible areas

Grab Dredger


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Dredging characteristics

• Dredging up to large depth’s

• Cannot create an even bottom

• Dredged material is loaded into barges

• Non-rock types of soil

• Suitable for debris and vegetation

Grab Dredger


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Areas with difficult access

Grab Dredger


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Groyne Construction

Grab Dredger


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Typical parts

• Different types and sizes to be fitted:

• Grabs

• Booms

• Positioning with spuds or anchors

Grab Dredger


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Standard grab (sand, clay, mud)

Cactus/Polyp grab (stones)

Grab Dredger


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Dredging cycle

• Lowering grab

• Closing grab

• Hoisting grab

• Turning crane towards barge

• Emptying grab into barge

• Turning back

Grab Dredger


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• Hard material

• Big boulders, blasted rock

• Removal of debris or vegetation

• Dredging depth


• Shipping

Grab Dredger


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Grab Dredger Small Mid-size Large

Dimensions L x Dr. 30 x 1.5 45 x 1.7 50 x 2

Dredging Depth m1 25 40 50

Grab size m3 2.5 - 5 5 - 15 15 - 50


Grab Dredger


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• Bucket ladder dredger (BLD)

• Dipper dredger

• Rock breaker

• Plough or bottom leveller

Other Mechanical Dredgers


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Bucket Ladder Dredger

• Revolving chain of buckets

• Swinging like a cutter suction dredger

• No spuds, position fixed by wires

• Buckets turning upside down to empty

• Discharge into barges


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Buckets are turning upside down to

discharge into barges

Bucket Ladder Dredger


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Bucket Ladder Dredger in Action


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Rock Breaker

• Hydraulic power to break rock

• Assists dredger on small spots

• Broken rock to be removed by excavator


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Plough or Bottom Leveller

• Towed by tug

• Assisting TSHD with removal of ridges and high spots

• Removal of soft material from small harbours

• Low production

• Cheap


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Water based

• Barges

• Work boats and launches

• Anchor pontoons, floating line pontoons

• Booster station

Other Equipment


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Survey launch

Multicat for handling and transport

A-frame for anchor handling


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Floating pipeline pontoons

Rubber floating pipeline

Use of floating pipeline


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Floating cover

Female Ball Joints Male

Rubber Floating Line


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Booster station


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Land based • Pipelines and valves

• Bulldozers, shovels, etc.

Other Equipment


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• Objective

• Types

• Typical Aspects

Environmental Dredgers


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Objective:


• Optimise precision

• Accurately dredging of thin layer

• Minimise disposal capacity by high concentration (minimisation of

dilution)

• Minimise turbulence and turbidity

• Safety: bring dredged bottom material via closed system to barge or

disposal area


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H H D Clean

Contaminated

Contaminated material is left behind, and falls in overdepth

Accuracy Aspects


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D increased, H not removed H (contaminated) removed

Accuracy Aspects


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Typical aspects


• Automation necessary

• Maximising concentration

• Controlling excavation level

• Controlling layer thickness

• Output level low due to:

• High accuracy

• Avoiding turbulence


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Types

• Environmental disc cutter dredger

Disc cutter head with closed bottom plate and shields

• Environmental auger dredger

Dual active rotating auger in enclosed area

• Horizontally closing grab

Grab sealed off when closed

• Hydraulic excavator fitted with closed visor bucket

• Encapsulated Bucket Ladder Dredger



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Disk bottom (cutter) dredger

disk cutterhead with closed bottom plate and shields



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Environmental Auger Dredger



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• Grab is horizontally closing

• Sealde off after closing



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Standard Grab


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Horizontally Profiling Grab


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Hydraulic excavator fitted with closed visor bucket


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Bucket Ladder Dredger with encapsulated bucket line


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THE END


factors effecting performance

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