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Deck Machinery

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Title: Deck Machinery


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Deck Machinery
  • Windlass
  • Mooring winches
  • Hatch cover openers (pull wire or hydraulic type)
  • Winches and derricks or cranes
  • Gangways and motors
  • Cargo pumps for LPG/LNG or chemical carriers
  • Whistle/Horn
  • Life boat winch and safety equip. drives

6
Anchor Handling
  • Efficient working of the anchor
    windlass is essential to the safety of the ship.
    Its design and performance is subjected to
    strict classification society rules. Basically
    they require that
  • Cable lifter brake shall be capable of
    controlling the cable and anchor when
    disconnected from the gearing at letting go. The
    Av. Speed of cable shall be 5-7 m/s.
  • The heaving capacity shall be 4-6 times the
    weight of one anchor at speeds between 9 and 15
    mts/minute. The lifting wt shall be between 20-70
    tonnes.
  • The braking effort obtained at the lifter shall
    at least 40 of the breaking strength of the
    cable.
  • The windlass must be capable of pulling the
    anchor from a depth of 25 of the total cable
    carried, i.e. 50 of the length of chain on one
    side.
  • It should be capable of lifting the anchor from
    82.5m to 27.5m at 9m/min.
  • Normal anchor handling equipment incorporates
    warp ends for mooring purposes with light line
    speed of up to 1m/sec.

7
Drives 1
  • Electric or Electro hydraulic drives are used
    for dry cargo
    deck machines
  • Electric drives
  • Should be totally enclosed
  • DC drives are still used because they got good
    torque range over the full speed though they need
    regular attn..
  • Control of contactor operated armature resistance
    is fully replaced with Ward Leonard system for
    good regulation especially at lowering loads (
    The present day Ward Leonard generator is driven
    by an AC motor)
  • DC motors may also be controlled by thyristors
    which converts AC to variable DC voltage
  • AC Induction motors can be wound rotor or cage
    type. Speed control being pole changing or rotor
    resistance change type. Another form of AC motor
    control being VFD drives which controls the
    applied frequency and voltage.

8
Drives 2
  • Hydraulic Systems provide a good means of
    distribution of power obtained from pump driven
    by a constant direction/speed AC motor. This oil
    can be made to drive thro hydraulic motors to
    power the actuating devices. Both constant
    delivery and variable delivery type pumps and
    motors are commonly used
  • The fixed output pumps can be of the Woodward
    hydraulic engine governor type which maintain
    reserve oil at pressure to cater to demands
  • Variable displacement pumps can be of axial or
    radial piston types where operational valves can
    be avoided.

9
Hydraulic System Design
  • Careful design, selection, layout, and
    installation of components essential for the
    trouble free operation It is very essential for
    all hydraulic systems be provided with
    interlocking arrangements for pump and motors so
    that control levers remain automatically in
    neutral to avoid inadvertent start ups. Overload
    protection thro relief valves to safeguard
    system at 30-40 over pressure Atmospheric
    contamination isolation, oil compatibility,
    system cleanliness, regular routine maintenance
    etc. can see thro long periods of trouble free
    operation

10
Conventional equipments
  • Conventional type of equipments are
  • Mooring windlass. Normally either an electric or
    Hydraulic motor drives 2 cable lifter and 2 warp
    ends. There are many designs but due to slow
    speed of cable lifter(3-5rpm) a slow speed worm
    gear and a single step spur gear between cable
    lifter and warp end is used
  • Anchor Capstans. Vertical capstans use a vertical
    shaft, with the motor and gearbox situated below
    the winch unit (usually below decks. With larger
    cables the capstan barrels is mounted separately
    on another shaft
  • 3. Winch windlasses. This arrangement uses
    a mooring winch to drive the windlass.
    Both port and starboard units are
    interconnected to facilitate standby and
    additional power should the situation
    arise

11
Control of Windlass
  • As the location is very vulnerable, the equipment
    shall demand less maintenance and the design and
    layout shall reflect this.
  • Design on adequate margin of the strength rather
    than on life is the main criteria while on the
    planning stage. Slipping clutches safe guard
    against shocks. Enclosed oil lubricated and open
    gears are common depending on sizes
  • Normally these are controlled locally like
    starting and manual application of brake while
    letting go the anchor etc.
  • But remote controls are getting popular in the
    recent times

12
Anchoring equipment
The anchoring equipment fitted to the majority of
vessels consists of two matched units, offering a
degree of redundancy. These units consists of an
anchor, chain (or for smaller vessels wire), a
gypsum or chain lifter wheel, brake, lift motor
and various chain stopper arrangements. When not
in he use the chain is stowed in a chain
locker. Systems fitted with wire are stowed on a
drum in the same way as winches.
  1. The windlass must be capable of pulling the
    anchor from a depth of 25 of the total cable
    carried, i.e. 50 of the length of chain on one
    side
  2. It should be capable of lifting the anchor from
    82.5m to 27.5m at 9m/min.

13
Chain locker
A false bottom is fitted to the chain locker
consisting of a perforated plate. This allows
water and mud to be removed from the space. The
end of the chain is attached to the hull by a
quick release mechanism known as the 'bitter
end'. The strength of this will not be
sufficient to prevent a run away unbraked chain.
The arrangement must be easily accessible.
14
Hawser
The chain is led overboard by a strengthened and
reinforced pipe called a Hawser. One of the
reasons for bow flare is to allow the anchor and
chain to lie well clear of the hull when in use,
preventing damage.
15
Chain stopper
For anchoring operations the stopper bar is
locked upright. When it is required to fix the
position of the chain the stopper is lowered into
the position shown. This allows the brake to be
released and is typically used for stowing the
anchor. chain stopper arrangements are not
designed to stop a runaway chain. Alternately an
arrangement known as the 'devil's claw' may be
used which has a forked locking piece. For
smaller vessels, and where extra security is
required bottle jacks with wire straps passed
though the chain may be used.
16
Chain
End pull will cause the link to collapse in. This
repeated many times will lead to fatigue failure.
Hence, stud linked chain is insisted upon
Here a stud is welded on one side in the
link to brace it against deformation. An
alternative to this albeit in limited use is
shown below. Chain sizing Each vessel is given
an equipment number which is calculated with use
of a formula and takes into account the vessels
size, underwater area and sail area. From this a
'look-up' table may be used to give an
appropriate size of cable. The diameter of the
chain may be read from this table and differs
depending on the grade of steel. This grade of
steel varies from U1 ( mild steel), U2 (Special
Steel) to U3 (extra special steel).
17
Chain
The size of cable that is to be used is found by
the use of a formula which is Equipment number
D2/3 2Bh A where D Displacement B
beam h Freeboard height of deckhouses over
B/4 wide A Transverse area including deckhouses
over B/4 wide
18
Ranging Anchor Chain
Ranging Anchor Chain During docking the anchor
chain is lowered from the chain locker to the
dock bottom and laid out for inspection. This
allows the inspection of the chain for broken or
lost chain studs. A random set of links are
measured from each shackle length ( Shackle
refers to a standard length- nominally 27.5m), of
chain joined to other shackle lengths by a
splitable link. There is an allowable wear limit
allowed nominally 12.
19
Anchor designs
Anchor shown below is of the 'flipper' type.
Regulations allows these to be smaller than
standard types used in many small to medium sized
tankers
20
Mooring equipment
  • Duties of warping capstans and mooring winches
    vary between 3-30 tonnes _at_ .3-.6 m/s and twice
    the speed for recovering light lines. Steel rope
    up to a max. circumference of 140 mm is used
  • Mooring winches tightens the wire up to the
    stalling capacity of the winch (normally 1.5
    times full load) then the load is held by the
    motor brake
  • Auto mooring winches incorporates controls which
    let off or overhaul at preset tension. There is a
    certain range of tension associated with each
    action. This is to limit the hauling capacity of
    the winch, safe guard against rope breakage, and
    slackness etc. Spring loaded gear wheels, torsion
    bars and fluid pressure sensing are common as
    sensing device in the auto system monitors
  • Normally locally controlled however remote
    control too is popular
  • To facilitate easy reversing spur gears are used
    however worm gearing is also not uncommon

21
Cargo Handling
  • Lift load at suitable speed
  • Hold the load from running back.
  • Lower the load under strict control.
  • Smoothly take up of slackness of sling.
  • Dropping the load as reqd.
  • Allow the winch to stall on oload and restart
    when the stress is relieved.
  • Have good acceleration and retardation.
  • Also when electrically driven
  • Lowering speed shall be safe for the motor
    armature
  • Stop running back in the event of power failure
  • Prevent the winch from restarting on power return
    w/o manually starting up.

22
Cargo Handling Drives
  • Electric and hydraulic systems quite common for
    the cargo winches
  • Electro-hydraulic cranes are self contained units
    with all machinery enclosed in the crane house.
    This protects it from the weather, corrosion and
    damage. The standard range covers lifting
    capacities from 25 to 90 tonnes, with outreaches
    up to 32 m. Each crane is normally tested
    electrically, hydraulically and mechanically
    before installation on board.

23
Derricks
  • For the conventional Union Purchase arrangement
    or the slewing derrick systems, standard cargo
    winches are used for all the activities like
    hoist, luff and slew.
  • Cargo winch nos. and capacity are decided in
    advance keeping in mind the no of hatches and the
    size to work.
  • The speed varies from 0.45 m/s at full load to
    1.75m/s at light load with 40 kw at full load of
    7 T and 20 kw for 3 T
  • Advantage of the derrick system is that only 2
    winches are reqd. and has a faster cycle time.
    But safe working load is less and takes quite
    some time to rig up the system prior to cargo
    work.
  • Slewing derrick system was an exception to the
    above and which could be rigged up and change in
    set up was faster.

24
Deck Cranes
25
Deck Cranes
  • Presently large no. of ships are fitted with the
    cranes which can be operational faster and spot
    the cargo easily.
  • Pole changing motors are being replaced with Ward
    Leonard system or Electro hydraulic system are
    popular.
  • Most crane makers incorporate a rope system for
    luffing and this is commonly rove to give a level
    luff. The cable geometry is so arranged that the
    Jib and luffing motor need not be designed to
    lift the load. However different heel angles can
    put a strain on the winch and shall be included
    while designing.
  • Some crane manufacturers use a hydraulic ram for
    the luff. Pilot operated leak valves ensure
    safety in the event of loss of pressure. Auto
    limiting devices are built-in to safeguard
    against operation beyond permissible jib radius.
    Some cranes are provided with varying speed
    depending on the load.

26
Crane Mounted Load Computer
To carry out a safe lifting operation a set of
variables must be known these consist of the
following The weight of the lift. The height of
the lift The Radius of the lift Obstructions
within the lift area The Sea State The newer
version of Cranes have a load computer which
measures the load weight, Boom Extension and Boom
angle. Form this it can compare computed load
against a model stored within its memory. As the
load approaches overload, alarms are sounded. The
computer has an extra mode which takes into
account operation with the fly boom. This load
computer is there as a safety factor and in no
way should be considered to replace proper
planning.
27
Weight Of lift
This may be either a known weight i.e. a weight
which is certified and clearly marked, or an
unknown estimated weight- in which case the
weight is estimated and a factor of safety
applied To be added to the lift weight is the
weight of the hook and lifting accessories before
calculations are carried out. For the hook this
is given as a test weight of 0.20 tonne for 10t
hook and headache ball 0.65 tonne for 50t 3
sheave block Note that unless the lift weight
is certified it is always classed as estimated in
all circumstances.
28
Height of the Lift.
  • This is measured form the boom pivot point and
    not the deck


29
Radius of Lift
  • In a similar fashion the radius is measured
    from the pivot point and not the centerline of
    the crane. The distance from the pivot to the
    centerline

30
Special instructions
  • Obstructions within lift area
  • The area not only where the load will be
    lifted and put down, but also the area covered
    whilst the crane is slewing. Should this be of
    particular concern a lifting plan should be
    created and discussed with the crane driver
    highlighting areas of concern and how best the
    Crane drive may avoid them. It should be
    understood that the crane driver may be unsighted
    of some of these obstructions therefore where
    this is considered to be a high risk a lift
    supervisor should be designated to guide the
    crane driver at all times.
  • Special consideration has to be given to
    lifts of unusual shape or where spreader bars are
    in use.

31
Special instructions
  • The Sea State
  • Vessel lift operations differ from shore
    based operations in that dynamic load forces have
    to be taken into consideration. The worst sea
    state condition considered to occur during the
    whole operation should be used and lift
    calculations based on that The Dynamic Loading
    factor stated in QGPS Lifting Equipment
    Regulations is 2.4 times for routine
    loading/unloading. A factor of 1.35 may be
    applied after written consent. maximum wind speed
    is given as 25knots and maximum wave height of 2m
  • Lifting tackle Inspections
  • A lifting tackle inspection by a competent person
    is required on all lifting accessories every 6
    months. However, it is also required that all
    lifting accessories are examined for defects
    before use and this includes all crane
    operations. Appendix C gives a listing of the
    failure parameters applicable to typical lifting
    accessories

32
Calculation of Boom extension
  • The easiest way to do the following is with
    graph paper with suitable scaling
  • However it is possible to calculate the
    required boom length.

33
Checking the Cranes Capability
34
Checking the Cranes Capability
  • Here we can see that at 20m radius/28.04m
    boom extension the lift capability is 11.9 tonne.
    For a 22m radius with same boom extension the
    lift capability is 10.5 tonne. As are lift is 6.4
    tonne the crane is suitable.
  • We therefore instruct the crane driver to Gib Up
    and Boom out to 27.5 m placing the Gib 2 metres
    above the lift
  • These instructions may also be used for shore
    crane operations. On the capability chart a
    darkline denotes the limit of stability and
    refers to lifting weights with the boom at right
    angles to the bed rather than over the cab. For
    shore operations the capability chart refers to
    full outrigger extension only and a separate
    chart must be in place if half outrigger
    extension is to be used

35
The Effects of Dynamic Loading
  • For this document 'Dynamic loading refers only to
    the effects of movement of the vessel due to
    rolling only. The effects of Pitching, lift and
    lower acceleration and deceleration, relative
    movement between vessel and platform from which
    weight is being lifted or lowered to is not
    considered.
  • Effects of Heel Angle

36
Sling Angles
The above shows the loading in slings depending
on the included angle. It can be seen that
fitting too short a pair of slings and thereby
creating too great an included angle can
substantially increase the loading in the sling
and cause it to fail . Hence should not consider
any lifting operation with an included angle
greater than 90 degrees and then should give a
1.5 factor for the slings i.e. the slings should
be at least 0.75 tonne each to lift the 1 tonne
weight
37
Hatch Covers
  • State-of-the-art hatch covers can be divided into
    three basic types
  • Lift-away hatch covers.
  • Rolling hatch covers
  • Hydraulic folding hatch covers
  • All these types share
  • Weather tightness
  • durability
  • optimized weight/strength ratio

38
Lift-away hatch covers.
Single-opening Multi-opening. Can be operated
by the ships crane or external help. Sealing
between hatch covers and coaming is generally
achieved by sliding rubber packing
39
Hydraulic Folding Types
The folding pair is operated by hydraulic
cylinders acting directly on the end hinge arms
which are connected at stools on the deck. When
the cylinders push the end panel up from the
closed position, the cover is folded and the
second panel, fitted with wheels, rolls on the
rails to the stowage position
40
Rolling types for combination/dry bulk carriers
  • Side-rolling hatch covers stow in a transverse
    direction while end-rolling types stow
    longitudinally. The traditional side-rolling
    cover consists of two panels per hatch, each
    panel rolling sideways on a pair of transverse
    ramps, thus presenting a minimum obstacle when
    loading. In some cases both panels can be stowed
    together on one side to further enhance access
    when loading and unloading. This alternative
    reduces daylight opening by approximately 50.
  • Rack and pinion drive  
  • Chain drive  
  • Roll-up-Roll are normally used for operation

41
Variable Frequency Drives
42
A variable-frequency drive (VFD)
  • Since the voltage is varied along with frequency,
    these are sometimes also called VVVF (variable
    voltage variable frequency) drives.
  • RPM 120f/p Variable frequency drive controllers
    are solid state electronic power conversion
    devices. The usual design first converts AC input
    power to DC intermediate power using a rectifier
    bridge. The DC intermediate power is then
    converted to quasi-sinusoidal AC power using an
    inverter switching circuit. The rectifier is
    usually a three-phase diode bridge, but
    controlled rectifier circuits are also used.
    Since incoming power is converted to DC, many
    units will accept single-phase as well as
    three-phase input power (acting as a phase
    converter as well as a speed controller) however
    the unit must be derated when using single phase
    input as only part of the rectifier bridge is
    carrying the connected load.

43
Variable Frequency Drives
  • AC motor characteristics require the applied
    voltage to be proportionally adjusted whenever
    the frequency is changed in order to deliver the
    rated torque. For example, if a motor is
    designed to operate at 400 volts at 50 Hz, the
    applied voltage must be reduced to 240 volts when
    the frequency is reduced to 30 Hz. Thus the
    ratio of volts per hertz must be regulated to a
    constant value (400/50 8 V/Hz in this case).
    For optimum performance, some further voltage
    adjustment may be necessary, but nominally
    constant volts per hertz is the general rule.
    This ratio can be changed in order to change
    the torque delivered by the motor.

44
VFD
  • The latest method used for adjusting the motor
    voltage is called pulse width modulation PWM.
    With PWM voltage control, the inverter switches
    are used to divide the quasi-sinusoidal output
    waveform into a series of narrow voltage pulses
    and modulate the width of the pulses.

45
Life Boat
Schematic Of Launch
46
Life boat.
When lowering no mechanical assistance except
gravity shall be applied. The only physical work
needed being release of winch hand brake hold at
the off position during the lowering sequence.
The centrifugal brake provides controlled speed
(36m/minute) to the lowering when hand brake is
released. If the operator looses balance and fall
off, the brake gets engaged due to the weight in
the handle the life boat shall remain
stationary at the place of stop. A ratchet
mechanism in the hoisting arrangement ensures
that the drum will not reverse and the boat fall
back into the water to provide safety in the
event of power failure while lifting.
47
Gravity davits
48
Skate
49
Totally Enclosed Machinery Propelled Survival
Craft
TEMPSC
50
Main Features of TEMPSC
51
Sirens whistles
Signal indicates the presence of the ship in poor
visibility or the vessels intension of movement.
Steam, air and electric whistles are commonly
used. Some have audible range of 9 nautical
miles. Air and steam operate on the same
principle viz. the working fluid to cause the
diaphragm to vibrate and the consequent sound
waves to be amplified in a horn. They operate
with pressures in the range of 6 40 bar with
air/steam consumption in the range of 25
35-lts/sec. The types of electrically operated
ones work on the principle of an electric motor
drives a reciprocating piston thro a gear train
and crank. This generate an air pressure which
operates a diaphragm In all the cases clean dry
medium is essential for the trouble free
performance of the whistle.
52
Water tight doors
Adequate water tight subdivisions of the ship is
effected by steel watertight bulkheads from
double bottom tank top to freeboard deck of the
ship. It may be necessary to provide doors in
some of this bulkheads, and these doors must be
properly watertight and be able to close and open
from both sides and from remote in the event of
emergency. Where a local hand operated pinion is
provided for opening or closing the door and an
extended spindle above the water line is provided
for remote operation. A vessel which have so many
water tight bulkheads pierced by water tight
doors below water line, a powered remote system
is essential for its operation. Hydraulic or
electric drive are common. Local control also
shall be available. In bridge control, maxm. of
20 doors shall be closed with in 60 secs. This
include a 10 sec audible alarm at each door
prior to closing. The alarm shall sound till each
door is fully closed. In these event too each
door shall be operated locally and on release of
local handle the door shall fall back closed.
There shall be indications of the status of the
doors at the bridge and at the manually operated
emergency pump at the bulk head deck.
53
Gas carriers
Liquefied gas carriers are classified as
suitable for transport of LPG and ammonia or LNG
or both if appropriately equipped. LPG term
for gasses such as propane, butane, propylene,
butylenes, C4- isomers. These can be liquefied at
modest pressures. LNG Methane and mixtures
containing ethane and traces of other
gasses. Liquefied chemical gas ammonia, vinyl
chloride, chlorine. The pressures are important
as upper critical pressure and temperature plays
an important role in deciding the tank design
These are the limiting feature. Critical
pressure The minimum pressure which would suffice
to liquefy a substance at its critical
temperature. Above the critical pressure,
increasing the temperature will not cause a fluid
to vaporize to give a two-phase
system. Similarly every gas has a critical
temperature above which a gas cannot be liquefied
irrespective of the pressure
54
Gas carriers principle
  • For temp down to -55C special carbon manganese
    low carbon steel for tanks and hull (sec.
    barrier)
  • Nickel alloyed high tensile steel is only allowed
    for temp below -55C.
  • Lower the temp. higher the Ni content
  • Ni as high as 9 is reqd. for -165C LNG
    transport or Austenitic steel is generally used
    for membrane type of tanks.
  • Same stringent regulation applies to insulation ,
    supports etc. Special wood and foam is used for
    this purpose.

55
Gas carriers operation
For LNG the boil off is used as fuel for the
engine. Pressurized vessel need simple / lesser
equipment for cargo discharge. However low
temperature vessels need complicated equipment
such as compressors, heat exchangers and lots of
secondary equipments and control gear. Most of
these are situated in deck house on the main deck
divided into 2 compartments namely compressor
room with liquefaction plant and a separate motor
room. The cargo pipe system consists of liquid,
vapor, condensate, drain, purge and vent lines.
Valves for remote closing are fitted at pipe
entry into tanks and at cross over manifold
positions. 2 or more compressors are fitted which
can cool down more than the estimated boil off
gas. Capacity to heat up the cargo while
discharging is important as usually the shore
pipes are designed to accept at -10C. Usually
submersible pumps are used in LNG tankers while
deep well pumps are common in LPG tanks. The
pumps being submerged do not allow hydraulic
fluid drives because of temperature. Submerged
pumps do not normally allow any NPSH
complications. The deep well pumps, if fitted
with electric motors shall be of type Ex e
(enhanced safety requirement compliant) or
hydraulic Submerged pumps are usually induction
motor driven and normally are harmless in that
environment .
56
Gas carriers operation
Gas freeing is essential before change of cargo.
This is done by 1)Tanks heated to atmospheric
temperature. Special vaporizer/ heater is used
or compressor heat is used. 2) Purging with inert
gas from an independent inert gas generator. IG
at 0.4 bar is sent via gas freeing line as gasses
are vented thro vent mast till the vented gasses
shows below explosive limit The tanks are then
gas freed usually using the inert gas blower with
fresh air. This is continued till vent shows out
CO2. The tanks are inspected for dirt and
polymers.
Tankers Ballast tanks are inerted to protect
those in the event of tank leaks. Capacity 125
of the cargo discharge rate.
57
Gas carriers operation
Fire prevention System Deck water spray system to
avoid for cooling in case of fire and protect the
ship structures against brittle failures if the
cargo leaks. Water sprays are operated by heat
sensing devices. Cargo deck house, manifold area
etc. are having dry powder and CO2 fire
extinguishers are provided to be operated
remotely. The gas carriers are if classified for
carrying chemicals, are to be provided with foam
fighting system also.

Potentially
the most serious situation occurs when the tank
is almost empty, Chances of mixing with air
causing explosive mixture formation. Hence 2 of
the cargo is left in the tank to maintain an
atmosphere entirely of cargo vapor. With no air
present and the atmosphere entirely of hydro
carbon, the tank is safe. Only when the tank
needs repair or cargo change the tank is inerted
and inspected. The cargo left over are used to
maintain the tank temperature so that undue
thermal stresses are not developed on the
structures. 0.25 -0.3 of the cargo is some
times allowed as boil of to be consumed for
boiler /engine use as reqd.
58
Maintenance of deck machinery
59
General
  • Objective of the maintenance schedule is to keep
    the equipment to its original condition as
    possible. The equipment manufacturer will provide
    maintenance schedule. But conditions very
    drastically between type of ships, cargo carried,
    ports of call, environment etc. and the schedule
    too shall vary accordingly.
  • A few minutes spent on operating and greasing the
    working parts when the lubricant has been washed
    out by rain or spray, can save many hours at a
    later date.
  • At suitable intervals inspection shall be carried
    out for checking any change in condition of the
    working parts and made good any gaps.
  • Elementary precautions shall see the equipment
    thro many trouble free years of service

60
Routines
  • Bearings. 2 stroke of the grease gun every six
    months is all what is normally needed. Once the
    routine is being done the problem arise while
    replacing the bearing due improper handling and
    other repairs.
  • Induction motors. Apart from bearing, attn is
    needed towards insulation resistance. If the
    value is close to 1 M ohm indicates moisture and
    the cause should be rectified, and insulation can
    be brought up by heating. If this value falls
    close to .25 m. ohm the motor should never be
    started unless insulation can be brought to many
    m. ohms. At times the winding is virtually short
    circuited and if no improvement is observed on
    drying up, winding need to be redone.
  • In the case of wound rotor type motors insulation
    of the rotor winding too need to be checked as
    before. The brush, guiding system with the spring
    and the ring should be checked. Should the brush
    needs replacement, new brush shall after proper
    bedding need be used. Care be taken to avoid
    ingress of carbon dust into vulnerable motor
    parts.

61
Routines contd.
  • DC motor needs regular inspection and cleaning to
    ensure commutator performance. Brushes are softer
    than that for the slip ring and a variety of
    graphite combinations are available . The
    commutator should be dark coppery brown, the gap
    between bars shall be clean. Due to prolonged use
    the copper shall wear out and whenever the mica
    starts protruding out it should be cut to effect
    a 1mm clearance. Quality of the carbon material
    is of paramount importance.
  • Insulation of the armature and field winding
    should be checked at proper intervals and very
    low ohmic values indicate major damage of the
    concerned windings.

62
Routines contd.
  • In the Ward Leonard set, on starting, if the
    generator runs on the reverse it can seriously
    affect the motor driving it. Drive couplings need
    no constant attn. However they need to be in
    perfect alignment.
  • Safety slipping clutches need proper friction
    pads at the correct pressure. Slippage due to
    presence of oil, grease and dirt can lead to
    over tightening and the concerned safety
    failures.
  • Normally fail safe braking system is provided
    where springs close the brake and power releases
    it. Needs cleanliness and gap adjustment.
    Whenever a friction pad needs replacement the
    whole set shall be changed. Where brake shows
    signs of over heating or excessive wear is
    noticed the same shall be investigated and
    corrected.

63
Routines contd.
  • Cables and terminations need to be inspected
    periodically. Cable terminations, bends and
    joints should be checked for signs of heat. Lugs
    and cable shall be correctly matched while
    fitting and the crimping tool shall be proper.
  • Control of the machinery are normally situated on
    deck locally where adverse effect of weather is
    predominant. Salt water corrosion and
    condensation is common. Operating gear shall be
    well maintained properly lubricated. Any sign of
    the effect of environment should be rectified.
    This applies to limit switches trip bars,
    emergency stop stations etc.
  • Extra care should be taken when working on live
    panels.
  • Anti condensation heaters whenever provided
    should be checked for the correct functioning.

64
Routines contd.
  • Open contactors should be maintained clean and
    any silver plating should never be ground. The
    magnet coils should be checked for looseness and
    vibration.
  • Block contactors seldom need maintenance if
    operated properly and cleanliness is maintained.
  • Relays and smaller contact comes in the form of
    sealed units. They seldom need replacement as the
    load is very small. Should they need replacement
    the specification need be strictly adhered to.
  • Thermal overload relays are made use of the
    distortion of a bimetallic strip to trip a
    circuit. In recent time a resistance changing
    semiconductor thermistors are used. Magnetic
    overloads work on the principle of over current
    attracts an armature tripping the circuits,

65
Routines contd.
  • Power regulation resistances may need attn when
    signs are visible for color, insulation damaged
    etc. If fan cooled power regulators are used the
    same may need normal attn.
  • Rectifiers, thyristors, etc need no spaecial
    maintenance other than cleanliness and inspection

66
Care to be taken with hydraulic system
  • Filtration and system cleanliness
  • One of the most difficult and controversial
    feature of hydraulic technology and remains the
    single factor in user education towards
    this. Basic filter construction varies from
    coarse metal mesh (100-150 microns) to high level
    filtration of (1 micron).
  • Generally 2 types filter body construction
    available.
  • LP working pressure up to 20 bar and
  • HP type with working pressure up to 400 bar.

67
Filtration terminology
  • Many methods indicating the filtering
    characteristics of the element exists. But these
    two are quite common.
  • Absolute rating based on 99 efficiency
  • Nominal rating based on an arbitrary efficiency,
    from a test curve showing the percentage of known
    size particles transmitted by the media. This
    shall be typically 95 and the particles stopped
    defines the nominal efficiency.
  • Pressure drop

68
Source of contamination
  • With proper procedures hydraulic system
    reliability is achieved in filthy environments
    viz. earth moving, mining and marine
    environments.
  • In any circuit debris may be present due to a.
    Inadequate preparation like welding or
    accidental damages of pipe runs or parts b.
    Ingress due to mishandling c. Self generated by
    the machines Of the above, a and b can aggravate
    the problems arising at c Equipment which are of
    an efficient design and well laid out components
    ease the task of maintenance.

69
Basic
  • Commissioning procedures, tank, piping equipment
    design, cooling, material selection, choice of
    the fluid etc add immensely to the behavior of
    the system.
  • This is highly true with hydraulic mineral oils
    containing special additives to cover lubricity,
    anti foaming, corrosion resistance, VI improver
    etc. when subjected To severe duty conditions as
    in marine appln., if not maintained proper , can
    lead to extensive service difficulties.

70
Deterioration of hydraulic fluid
  • Water was used earlier , even now like in lock
    gate or moving bridge operation water is used as
    the hydraulic fluid. Due to inherent problems
    associated with lubrication ,rusting, operating
    temperature range do not find favor with.
  • Present day practice is to use straight mineral
    oils with additives to enhance properties of
    oxidation stability, film strength, rust
    prevention, foam resistance demulsibility, pour
    point depressant anti wear property, VI
    improver, lubricity etc.
  • Mineral oils degenerate very slowly but rigorous
    marine duty conditions make this oil susceptible
    to decay in presence of products of corrosion or
    metal wear. Oxidation products tend to increase
    the viscosity and cause sludge deposit. Also tend
    to encourage formation of emulsion when traces of
    water is present.
  • Water can promote rusting which can cause immense
    damage to the system. Condensation, leaky shaft
    seals, system coolers etc are the source which
    need periodic attn or when ever defects are
    detected.
  • Fine metal wear is inevitable which are abrasive
    is removed by fine filters along with rust and
    any grits which find its way into the system

71
Fault Finding
  • Ships deck equipment like windlass and mooring
    winches employs relatively simple control schemes
    and a logical method of elimination is the
    quickest method.
  • Electrical and electronic equipments are usually
    provided with manufacturers control charts which
    details the logical steps for the maintenance.
  • The simplest of suspects like a jammed limit
    switch, a blown control fuse, weak relay coil, a
    loose or broken wire etc should never be
    overlooked.
  • Mechanical or pneumatic timing devices can be
    checked with power off however electrical timing
    circuits or encoders needs to be energized.

72
Fault Finding contd.
  • A detailed knowledge and operating experience of
    a control system is essential for speedy faulty
    finding, a calm orderly and logical approach will
    definitely produce results.
  • Disorganized check and try shortcuts can
    produce some additional defects and make the task
    more difficult and time consuming and must be
    avoided at any cost.
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