Deck Machinery
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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…
Anchor Handling
Efficient working of the anchor windlass is essential to the safety of the ship.
It’s design and performance is subjected to strict classification society rules.
Basically they require that
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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 57 m/s.
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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.
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The braking effort obtained at the lifter shall at least 40% of the breaking
strength of the cable.
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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.
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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.
Drives 1
Electric or Electro hydraulic drives are used for dry
deck machines
cargo
Electric drives
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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.
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.
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
Conventional equipments
•
Conventional type of equipments are
1.
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
2.
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
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
Anchoring equipment
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.
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.
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.
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.
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.
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).
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
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%.
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
Mooring equipment
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Duties of warping capstans and mooring winches vary between 3-30
tonnes @ .3-.6 m/s and twice the speed for recovering light lines.
Steel rope up to a max. circumference of 140 mm is used
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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
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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
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Normally locally controlled however remote control too is popular
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To facilitate easy reversing spur gears are used however worm
gearing is also not uncommon
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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 o’load 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.
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.
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.
Deck Cranes
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.
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.
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.
Height of the Lift.
This is measured form the boom pivot point
and not the deck
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
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.
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
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.
Checking the Cranes Capability
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
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
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
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
Lift-away hatch covers.
Single-opening & Multi-opening. Can be operated by
the ship’s crane or external help. Sealing between
hatch covers and coaming is generally achieved by
sliding rubber packing
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
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%.
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Rack and pinion drive
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Chain drive
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Roll-up-Roll are normally used for operation
Variable Frequency Drives
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 threephase 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.
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.
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.
Life Boat
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.
Gravity davits
Skate
Totally Enclosed Machinery Propelled Survival Craft
TEMPSC
Main Features of TEMPSC
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.
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.
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, C4isomers. 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
Gas carriers principle
• For temp down to -55’C special carbon manganese low
carbon steel for tanks and hull (sec. barrier)
• Nickel alloyed high tensile steel is only allowed for temp
below -55’C.
• Lower the temp. higher the Ni content
• Ni as high as 9% is reqd. for -165’C 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.
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 -10’C. 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 .
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.
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.
Maintenance
of
deck machinery
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
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.
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.
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.
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.
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,
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
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.
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
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.
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.
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
Fault Finding
• Ship’s 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 manufacturer’s 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.
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.