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Marine Auxiliary Machinery

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Marine Auxiliary Machinery Chapter 9 Lesson 5 Deck Machinery Cargo Handling By Professor Zhao Zai Li 05.2006 CARGO HANDLING (1) The duty of a deck winch is to lift ... – PowerPoint PPT presentation

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Title: Marine Auxiliary Machinery


1
Marine Auxiliary Machinery
  • Chapter 9 Lesson 5
  • Deck Machinery
  • Cargo Handling

By Professor Zhao Zai Li 05.2006
2
CARGO HANDLING (1)
  • The duty of a deck winch is to lift and lower a
    load by means of a fixed rope on a barrel, or by
    means of whipping the load on the warp ends to
    top or luff the derricks, and to warp the ship.
  • In fulfilling these duties it is essential that
    the winch should be capable of carrying out the
    following requirements
  • (a) lift the load at suitable speeds
  • (b) hold the load from running back

3
CARGO HANDLING (1)
  • (c) lower the load under control
  • (d) take up the slack on the slings without undue
    stress
  • (e) drop the load smartly on the skids by
    answering the operators
  • application without delay
  • (f) allow the winch to be stalled when
    overloaded, and to start up
  • again automatically when the stress is
    reduced
  • (g) have good acceleration and retardation

4
CARGO HANDLING (2)
  • In addition when the winch is electrically driven
    the requirementsare
  • (a) prevent the load being lowered at a speed
    which will damage the motor armature
  • (b) stop the load running back should the power
    supply fail
  • (c) prevent the winch starting up again when the
    power is restored until the controller has been
    turned to the correct position.

5
CARGO HANDLING (3)
  • Hydraulic winch systems are now quite common but
    electric
  • drives for cargo winches and cranes are most
    widely used.
  • For the conventional union purchase cargo
    handling arrangement or for slewing derrick
    systems handling loads up to 20 tonne, standard
    cargo winches are normally used for hoist,topping
    and slewing motions, the full load duties varying
    from 3-10 tonne at 0.65 to 0.3 m/sec.

6
CARGO HANDLING (4)
  • For the handling of heavy loads, although this
    may be accomplished with conventional derrick
    systems using multipart tackle, specially
    designed heavy lift equipment is available.
  • Thewinches used with these heavy lift Systems
    may have to be specially designed to fit in with
    the mast arrangements and the winch duty pull may
    be as high as 30 tonne.

7
Cargo winches (1)
  • It is usual to select the number and capacity of
    and to group the
  • winches in such a way that within practical
    limits,all hatches may be worked simultaneously
    and having regard to their size (and the hold
    capacity beneath them) work at each is carried
    out in the same period.
  • Reduction of the cycle time during cargo handling
    is best accomplished by the use of equipment
    offering high speeds say from 0.45 m/see at full
    load to 1.75 m/sec light, the power required
    varying from 40 kW at 7 tonnes to 20 kW at 3
    tonnes this feature is available with
    electro-hydraulic and d.c. electric drives as
    they offer an automatic load discrimination
    feature.

8
Cargo winches (2)
  • However, the rationalisation of electrical power
    supply on board ship has resulted in the
    increased use of a. c. power and the majority of
    winch machinery now produced for cargo handling
    utilises the polechanging induction motor.
  • This offers two or more discrete speeds of
    operation in fixed gear and a mechaincal change
    speed gear is normally provided for half load
    conditions.
  • Normally all modern cargo handling machinery, of
    the electric or electrohydraulic type,is designed
    to fail safe.
  • A typical example of this is the automatic
    application of the disc brake on an electric
    driving motor should the supply fail or when the
    controller is returned to the OFF position.

9
Derricks (1)
  • Most older ships and some recent ones use winches
    in conjunction with derricks for working cargo.
  • The derricks may be arranged for fixed outreach
    working or slewing derricks may be fitted.
  • A fixed outreach system uses two derricks, one
    topped to a position over the ships side and
    the other to a position over the hold.
  • Figure 9.9 shows the commonest arrangement
    adopted, known as Union Purchase rig.

10
Derricks (2)
  • The disadvantages of the fixed outreach systems
    are
  • that firstly if the outreach requires
    adjustment cargo work must be interrupted, and
    secondly the load that can be lifted is less than
    the safe working load of the derricks since an
    indirect lift is used.
  • Moreover considerable time and man power is
    required to prepare a ship for cargo working.

11
Figure 9.9
Union purchase rig
12
Derricks (3)
  • The main advantages of the system are that only
    two winches are required for each pair of
    derricks and it has a faster cycle time than the
    slewing derrick system.
  • The slewing derrick system, one type of which is
    shown in Figure 9.10, has the advantages that
    there is no interruption in cargo work for
    adjustments and that Cargo can be more accurately
    placed in the hold however in such a system
    three winches are required for each derrick to
    hoist luff and slew.

13
Figure 9.10
Slewing derrick
14
Deck cranes (1)
  • A large number of ships are fitted with deck
    cranes.
  • These require less time to prepare for working
    cargo than derricks and have the advantage of
    being able to accurately place (or spot) cargo in
    the hold.
  • On container ships using ports without special
    container handling facilities, cranes with
    special container handling gear are essential.

15
Deck cranes (2)
  • Deck-mounted cranes for both conventional cargo
    handling and grabbing duties are available with
    lifting capacities of up to 50 tonnes.
  • Ships specialising in carrying very heavy
    loads,however, are invariably equipped with
    special derrick systems such as the Stulken
    (Figure 9.11).
  • These derrick systems are capable of lifting
    loads of up to 500 tonnes

16
Figure 9.11
Stulken derrick (Blohm and Voss)
17
Deck cranes (3)
  • Although crane motors may rely upon pole changing
    for speed
  • variation, Ward Leonard and
    electro-hydraulic controls are those
  • most widely used.
  • One of the reasons for this is that pole-changing
    motors can only give a range of discrete speeds
    but additional factors favouring the two
    alternative methods include less fierce power
    surges since the Ward. Leonard motor or the
    electric drive motor in the hydraulic system run
    continuously and secondly the contactors required
    are far simpler and need less maintenance since
    they are not continuously being exposed to the
    high starting currents of
  • pole-changing systems.

18
Deck cranes (4)
  • Deck cranes require to hoist, luff and slew and
    separate electric or hydraulic motors will be
    required for each motion.
  • Most makes of crane incorporate a rope system to
    effect luffing and this is commonly rove to give
    a level luffin other words the cable geometry is
    such that the load is not lifted or lowered by
    the action of luffing the jib and the luffing
    motor need therefore only be rated to lift the
    jib and not the load as well.

19
Deck cranes (5)
  • Generally, deck cranes of this type use the
    Toplis three-part reeving system for the hoist
    rope and the luffing ropes are rove between the
    jib head and the superstructure apex which gives
    them an approximately constant load, irrespective
    of the jib radius.
  • This load depends only on the weight of the jib,
    the resultant of loads in the hoisting rope due
    to the load on the hook passes through the jib to
    the jib foot pin (Figure 9.12(a)).

20
Figure 9.12
Rope lift cranes-resultant loads when hoisting
21
Deck cranes (6)
  • If the crane is inclined 5 in the forward
    direction due to heel of the ship the
    level-luffing geometry is disturbed and the hook
    load produces a considerable moment on the jib
    which increases the pull on the luffing rope
    (Figure 9.12(b)).
  • In the case of a 5 tonne crane the pull under
    these conditions is approximately doubled and the
    luffing ropes need to be over-proportioned to
    meet the required factor of safety.

22
Deck cranes (7)
  • If the inclination is in the inward direction and
    the jib is near minimum radius there is a danger
    that its weight moment will not be sufficient to
    prevent it from luffing up under the action of
    the hoisting rope resultant.
  • Swinging of the hook will produce similar effects
    to inclination of the crane.

23
Deck cranes (8)
  • In the Stothert Pitt Stevedore
    electro-hydraulic crane the jib is luffed by one
    or two hydraulic rains.
  • Pilot operated leak valves in the rams ensure
    that the jib is supported in the event of
    hydraulic pressure being lost and an automatic
    limiting device is incorporated which ensures
    that maximum radius can not be exceeded.
  • When the jib is to be stowed the operator can
    override the limiting device.
  • In the horizontal stowed position the cylinder
    rods are fully retracted into the rams where they
    are protected from the weather .

24
Deck cranes (9)
  • Some cranes are mounted in p airs on a common
    platform which can be rotated through 360º .
  • The cranes call be operated independently or
    locked together and operated as a twin-jib crane
    of double capacity", usually to give capacities
    of up to 50 tonnes.
  • Most cranes can, if required, be fitted with a
    two-gear selection to give a choice of a faster
    maximum hoisting speed on 1ess than half load.

25
Deck cranes (10)
  • For a 5 tonne crane full load maximum hoisting
    speeds in the range 50-75 m/min are available
    with slewing speeds in the range1-2 rev/min.
  • For a 25 tonne capacity crane, maximum full load
    hoisting speeds in the range 20-25 m/min are
    common with slewing
  • speeds again in the range 1-2 rev/min.
  • On half loads hoisting speeds increase two to
    three times.

26
Drive mechanism and safety features (1)
  • In both electric and electro-hydraulic cranes it
    is usual to find that the crane revolves on
    roller bearings.
  • A toothed rack is formed on them periphery of the
    supporting seat and a motor-driven pinion meshes
    with the rack to provide drive.
  • Spring-loaded disc or band brakes are fitted on
    all the drive motors.
  • These are arranged to fail safe in the event of a
    power or hydraulic failure.

27
Drive mechanism and safety features (2)
  • The brakes are also arranged to operate in
    conjunction with motor cut-outs when the crane
    has reached its hoisting and luffing limits, or
    if slack turns occur on the hoist barrel.
  • In the case of the electro-hydraulic cranes it is
    normal for one electric motor to drive all three
    hydraulic pumps and in Ward-Leonard electric
    crane systems the Ward-Leonard generator usually
    supplies all three drive motors.
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