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Marine Auxiliary Machinery

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Marine Auxiliary Machinery Chapter 9 Lesson 1 Deck Machinery General By Professor Zhao Zai Li 05.2006 Deck machinery (1) The range of deck machinery is extensive and ... – PowerPoint PPT presentation

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Title: Marine Auxiliary Machinery


1
Marine Auxiliary Machinery
  • Chapter 9 Lesson 1
  • Deck Machinery
  • General

By Professor Zhao Zai Li 05.2006
2
Deck machinery (1)
  • The range of deck machinery is extensive and
    varied, it can be divided broadly into
  • Anchor handling (windlasses and capstans).
  • Mooring (winches and capstans).
  • Cargo handling (winches and cranes).
  • The basic requirement of all the above is to
    control loads associated with chain cable or wire
    rope and whilst each type of equipment has its
    own operational requirements, certain aspects of
    design and operation are common.

3
Deck machinery (2)
  • Most deck machinery is idle during much of its
    life and due to this intermittent duty
    requirement, gears and drives are normally
    designed to a limited rating of one half to one
    hour.
  • Despite long periods of idleness, often in severe
    weather conditions, the machinery must operate
    immediately, when required.

4
Deck machinery (3)
  • It is essential that deck machinery should
    require minimum maintenance.
  • Totally enclosed equipment with oil bath
    lubrication for gears and bearings is now
    standard but maintenance cannot be completely
    eliminated and routine checking and greasing
    should be carried out on a planned basis.
  • Prime movers may be used to perform more than one
    basic duty.

5
Deck machinery (4)
  • For example, mooring winches are often combined
    with windlass units so that one prime mover
    drives both.
  • The port mooring winch motor can thus be used to
    drive the starboard windlass and vice versa.
  • This applies also to the power supply where
    generators or hydraulic pumps are also
    cross-connected.

6
Deck machinery (5)
  • There are many instances where remote or
    centralised control is of great advantage, for
    example, the facility for letting go anchor from
    the bridge under emergency conditions, the use of
    shipside controllers with mooring winches or the
    central control position required for the
    multiwinch slewing derrick system.
  • The three most common forms of main drive used on
    deck auxiliaries are steam, electric and
    hydraulic.

7
Deck machinery(6)
  • When fitted, steam auxiliaries are frequently of
    the totally enclosed type using forced or splash
    lubrication or a combination of both.
  • A typical arrangement has an oil pump driven from
    the crankshaft supplying pressure oil to the
    crankshaft and connecting rod bearings whilst
    crossheads, eccentrics and gearing are splash
    lubricated from the sump or drip trays.

8
Deck machinery (7)
  • The steam cylinders and valves are not normally
    lubricated as, due to the low working pressure
    and condensation, steam temperatures encountered
    on deck rarely exceed 180º C.
  • A superheated steam supply creates problems with
    cylinder lubrication and in any event has little
    effect on non-expansive working.
  • Inlet steam temperatures are limited for use with
    cast iron cylinders by Classification Society
    rules.
  • Full load crankshaft speeds are normally between
    90-160 rev/min increasing to twice this figure
    for light line duties.

9
Deck machinery (8)
  • An alternative form of steam drive is the
    reversing steam turbine which is illustrated in
    Figure 12.1.
  • This machine requires less maintenance and it is
    able to accept higher steam pressures and
    temperatures, (up to 24 bar,290º C) directly
    through a reducing valve from the main boilers,
    thus increasing turbine efficiency and minimising
    its size and weight.
  • On large equipment, even though the turbine has
    to be geared down from a normal full load speed
    of 2000-2500 rev/min there is a saving in total
    weight when compared with engine driven
    equipment.

10
Deck machinery (9)
  • As illustrated in Figure 12.1, the turbine shaft
    and rotor are supported in anti-friction
    bearings the coupling end bearing is grease
    lubricated and the governor mechanism and
    location bearing are splash oil lubricated.
  • Although the bearings warm up rapidly due to
    conduction of heat along the shaft from the
    exhaust casing, normal lubricating oils and
    greases have proved satisfactory.

11
Deck machinery(10)
  • Both reciprocators and turbines, as used on
    supertankers,drive the 1argest deck machinery in
    service.
  • This equipment is normally locally controlled at
    the machinery position, however, it is of great
    advantage to have shipside control for both
    windlass and mooring winch operation and this
    can be simply achieved by the use of push pull
    hydraulic mechanisms which are effective up to
    approximately 45m.

12
Figure 9.1
Sectional arrangement of reversing steam turbine
13
Electric drives (1)
  • Electric drives are most commonly used for deck
    machinery.
  • The motors are generally totally enclosed,
    watertight and in most cases embody a spring
    applied, magnetically released, fail safe disc
    brake.
  • The direct current motor, although it is
    relatively costly and requires regular brushgear
    maintenance, is frequently used where the
    characteristic flexibility of control may be used
    to good advantage.

14
Electric drives (2)
  • The control of d.c. motors by
    contactor-switched armature resistances, common
    in the days when ships supplies were mainly d.
    c., has now largely been superseded by a variety
    of Ward Leonard type control systems which give a
    better, more positive control particularly for
    controlled lowering of loads.
  • The Ward Leonard generator may be driven by
    either a d. c. or an a. c. motor.

15
Electric drives (3)
  • The most important feature of d. c. drive is its
    efficiency, particularly in comparison with a. c.
    drives, when operating at speeds in the lower
    portion of its working range.
  • The d. c. motor is the only electric drive at
    present in production which can be designed to
    operate in a stalled condition continuously
    against its full rate torque and this feature is
    used extensively for automatic mooring winches of
    the live motor type.

16
Electric drives (4)
  • The majority of d.c. winch motors develop full
    output at speeds of the order of 500 rev/min and
    wherever necessary are arranged to run up to two
    to four times this speed for light line duties.
  • Windlass motors on the other hand do not normally
    operate with a run up in excess of 21 and
    usually have a full load working speed of the
    order of 1000 rev/min.

17
Electric drives (5)
  • D.C. motors may also be controlled by static
    thyristor converters which convert a.c.
    supply into a variable d. c. voltage of the
    required magnitude and polarity for any required
    armature speed.
  • These converters must be of a type capable of
    controlled rectification and inversion with
    bi-directional current flow if full control is to
    be obtained (Figure9.2) .

18
Figure 9.2
Load/speed characteristic of Ward Leaoard
thyristor controlled winch.
19
Electric drives (6)
  • A.C. motors, either wound rotor or cage, are
    also in common use.
  • With these the speed may be changed by means of
    pole changing connections or, in the case of the
    wound rotor induction motor, by changing the
    value of the resistance connected to the rotor.
  • Both methods involve the switching of high
    currents at medium voltage in several lines
    simultaneously and the use of multi pole
    contactors is common.
  • These drives offer a very limited choice of only
    two or three discrete speeds such as 0.65,0.325
    and 0.1025 m/sec corresponding to 4.8 and 24 pole
    operation.

20
Electric drives (7)
  • The wound rotor type is slightly more flexible in
    hoist control but, as with the resistance
    controlled d.c. motor, difficulty is experienced
    in providing effective control of an overhauling
    load e.g lowering a suspended load.
  • These disadvantages are often outweighed by lower
    cost, particularly of the cage induction motor.
    in comparison with the more flexible d.c.
  • Typical performance curves are shown in Figure
    9.3.

21
Figure 9.3
Performance curves of a 3 tonne winch.
A C Pole-changing cage motor.
22
Electric drives (8)
  • Another form of induction motor control system is
    based on the relationship between output torque
    and applied voltage, the torque being
    proportional to the voltage squared.
  • The controller takes the form of a three-phase
    series regulator with an arm in each supply line
    to the motor.
  • A stable drive system can only be achieved by
    this means if a closed loop servo control system
    is used in conjunction with a very fast acting
    regulator which automatically adjusts the output
    torque to suit the load demand at the set speed.

23
Electric drives (9)
  • Control of an overhauling load is possibly by
    means of injection braking techniques.
  • A combined system employing both these control
    principles can provide full control requirements
    for all deck machinery.
  • The a. c. drives described operate at the supply
    frequency and consequently rapid heating of the
    motor will occur if the drive is stalled when
    energised .
  • The majority of a.c. motors on deck machinery run
    at a maximum speed corresponding to the 4 pole
    synchronous speed of 1800 rev/min on a 60 Hz
    supply.

24
Electric drives (10)
  • These speeds are similar to the maximum speeds
    used with d.c. drives and the bearings and shaft
    details tend to be much the same.
  • The motor bearings are normally grease
    lubricated however, in some cases where the
    motor is flange mounted on an oil bath gearcase,
    the driving end bearing is open to the gearcase
    oil and grease lubrication is not required.
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