Marine engineering vol 2 part 16

MARINE ENGINEERING PRACTICE Volume Part 16 SHIP'S GEAR: A REVIEW OF DECK MACHINERY by D H BEATTIE and W M SOMERVILLE THE INSTITUTE OF MARINE ENGINEERS Published by The Institute of Marine Engineers 80 Coleman Street London EC2R 5BJ Copyright © 1978 The Institute of Marine Engineers A Charity Registered in England and Wales Reg No 212992 Reprinted 1991 Reprinted 1994 Reprinted 1998 Reprinted 2000 All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form of by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher Enquiries should be addressed to The Institute of Marine Engineers ISBN: 900976 78 Printed by Hobbs the Printers in the UK CONTENTS 1.1 1.2 1.3 2.1 2.2 3.1 3.1.1 3.1.2 3.2 3.3 3.3.1 3.3.2 3.3.3 4.1 4.2 4.2.1 4.2.2 4.2.2.1 4.2.2.2 4.2.2.3 4.2.2.4 4.2.2.4.1 4.2.2.4.2 4.2.2.4.3 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.9.1 5.9.2 5.9.3 5.9.4 5.9.5 5.9.6 Anchor Handling Equipment Windlasses WinchWindlass Anchor Capstan Mooring Equipment Non-automatic MooringWinches Automatic MooringWinches Cargo Handling Equipment Derrick Rig Systems Fixed Outreach Systems SwingingDerrick Rigs Heavy Lifting Systems Deck Cranes Cargo Cranes (hook) Twin Cranes Grabbing Cranes Control of Deck Equipment Steam Electrical Control Systems Direct Current Supplies AC Systems Squirrel CageMotors Wound Rotor Induction Motors Ward Leonard Controls for AC Ships Electronic Control Systems Electronic Control of Ward Leonard Systems Direct Electronic Control of AC Motors Direct Electronic Control of DC Motors Maintenance General Motor Bearings Squirrel CageInduction Motors Wound Rotor Induction Motors DC Motors Ward Leonard Sets Brakes Cable terminations Controls Open Contactors Block Contactors Relays Resistances Rectifiers Thyristors Fault fmding Page I 2 4 6 7 10 10 10 13 17 17 18 18 24 24 27 30 35 37 39 39 46 46 46 47 47 48 49 49 51 51 52 53 53 54 55 55 57 LIST FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG 12345678910 11 12 13 14 - OF ILLUSTRATIONS Typical windlass arrangement Typical winch/windlass arrangement Typical anchor capstan arrangement Union purchase rig Patented swinging derrick system Heavy derrick rig Patented heavy lift derrick A S-ton deck crane Two 1S-ton twin deck cranes Heavy lift deck crane combined with S-ton deck crane Typical electro-hydraulic grab Typical 4-rope grab Steam valves for one double acting cylinder of a two-cylinder steam engine Back pressure valve for automatically regulating differential pressure across mooring winch engine FIG.15 - Relationship between speed and load for shunt, series and compound d.c motors at rated supply voltage FIG.16 - Variation of speed with load for various resistances in series with shunt motor armature at fixed field strength FIG 17 - Contactor switched series resistance control of D.C winch FIG 18 - Single-speed A C motor reversing drive FIG 19 - Typical torque/speed curves for single and double-cage rotor induction motors FIG 20 - Two-speed reversing power circuit for A.C motor with independent windings FIG 21 - Two-speed reversing power circuit for A.C motor with tapped winding FIG 22 - Schematic diagram for three-speed pole-changing cargo winch induction motor FIG 23 - Typical load/speed characteristics for a slipring induction motor with rotor resistance control FIG 24 - A C slipring motor control system for windlass drive FIG 25 - Basic Ward Leonard control system FIG 26 - Speed/load characteristic of basic Ward Leonard system FIG 27 - Modified Ward Leonard control system FIG 28 - Speed/load characteristic of modified Ward Leonard system FIG 29 - Control schematic for hoist, luff and slew motions of Ward Leonard driven deck crane FIG 30 - Differential crane limit switch arrangement FIG 31 - Slack rope switch FIG 32 - A selection of thyristors, illustrating range and encapsulation FIG 33 - Typical thyristor characteristics FIG 34 - The control of voltage and power by delaying the thyristor gate signal FIG 35 Schematic power circuit for the thyristor control of a Ward Leonard drive FIG 36· Thyristor and diode reversing drive for squirrel cage induction motor FIG 37 - Back-to-back thyristor reversing drive for slipring induction motor FIG 38 - Torque/speed curves for thyristor-controlled induction motor drive FIG 39 - Full bridge thyristor power circuit FIG 40 - Phase and d.c voltages relating (0 full thyristor bridge at firing pulse delays of 0° 30° 60° 90° and 120° FIG 41 - Transformer-fed half-bridge circuit FIG.42 - Voltage-wave form from controlled transformer-fed half bridge FIG 43 -Armature reversing thyristor motor control scheme FIG 44 - Field reversing thyristor motor control scheme FIG.45 - 'Back-to-Back' bridge or 'static' thyristor motor control scheme FIG 46 -A Typical Arrangement of one type of watertight motor brake The authors would like to thank the undernoted permission to reproduce illustrations FIG I FIG FIG FIG FIG FIG FIG FIG FIG FIG.10 FIG 11 FIG 12 companies for their kind Clarke Chapman Marine Clarke Chapman Marine Clarke Chapman Marine Clarke Chapman Marine Cargospeed Equipment Ltd British Standards Institution Blohm & Voss A G Clarke Chapman Marine Clarke Chapman Marine Clarke Chapman Marine Clyde Booth - Rodley Butters Cranes Ltd INTRODUCTION This booklet describes electrical and steam-powered machinery including its control system Hydraulic power transmission is covered in Marine Engineering Practice Volume I Part - Hydraulic Power Transmission in Marine Machinery by C.M Joy C.Eng and electric power is covered in Electricity Applied to Marine Engineering by W Laws The range of deck machinery currently in use is extensive and varied to suit the owner's particular requirements However, the equipment generally used can be classified into three categories: 1) Anchor handling equipment; 2) Mooring equipment; 3) Cargo handling equipment Although other types of deck machinery are in use e.g towing winches, trawl winches, etc, it is not the intention to discuss these highly specialized machines, but merely to describe, in general terms, the type of equipment to be found on the decks of most modern vessels ANCHOR HANDLING EQUIPMENT 1.1 WINDLASSES (see Fig 1) The efficient working of the anchor windlass is essential to the safety of the ship and therefore its design and performance is subject to the approval of the appropriate classification society Classification society rules governing windlass performance vary Basically they require that: a) the windlass cable lifter brakes are able to control the running anchor and cable when the cable lifter is disconnected from the gearing during "letting go"; average cable speeds vary between 5-7.5 m/s (1000-1500) during this operation; b) the windlass can heave a certain weight of cable at a specified speed; this "full load" varies but is generally between and times the weight of one anchor and the speed of haul at full load is usually between 0.12-0.2 m/sec (25-40 ft/min) The normal windlass arrangement utilizes one prime mover to drive two declutchable cablelifters and also two warping ends The warping ends are not declutchable and rotate continuously when the windlass is in use When mooring, light line speeds of 0.75-1.0 m/sec (150-200 ft/min) are required Due to the low speed of rotation of the cablelifter whilst heaving anchor (2-7 rev/min), a high gear reduction is required when the windlass is driven by a high-speed electric or hydraulic motor This reduction is generally obtained by the use of a high-ratio worm gear, followed by one or two steps of spur gearing between the warping end shaft and the cable lifter Alternatively, multi-steps of spur gearing are used As windlasses are required for intermittent duty only, the gearing is designed with an adequate margin on strength rather than wear Slipping clutches are commonly fitted on electrically driven windlasses, either between the motor and the gearbox or incorporated in the gearbox This avoids the inertia of the driving motor being transmitted through the gear system in the event of shock loading on the cable Such shocks can occur, for example, when the anchor is pulled hard into the hawse pipe when being housed Windlasses are normally controlled from a local position, the operator manually applying the cablelifter brake, as required, to control the speed of the running cable Whilst heaving anchor, the operator is positioned at the windlass or at the ships side if he needs to watch the anchor being housed Remotely cOntrolled systems are available which permit all normal windlass functions to to be carried out from the bridge, thus obviating the need for crew members to be on standby duty on the forecastle for long hours while the ship is negotiating an estuary or other restricted waterway The windlass is in the most vulnerable position as far as exposure to the elements is concerned and should be designed and constructed so that maintenance is reduced to the absolute minimum Normally primary gearing is enclosed and splash lubricated, maintenance being limited to pressure grease points for gunmetal sleeve bearings However, due to the large size of the final set of bevel or spur reduction gears, and the clutching arrangements required, these gears are often of the open type and are lubricated with open gear compound 1.2 WINCH WINDLASS UNIT This arrangement (Fig 2) uses a forward mooring wi!1ch to drive a windlass unit thus reducing the number of prime movers required The port and starboard unit can, if required, be interconnected mechanically by means of clutches to provide the following facility: a) b) a standby drive should one prime mover fail; the power of both prime movers to one windlass should this be required 1.3 ANCHOR CAPSTAN With this type of equipment the driving machinery is situated below deck and the cablelifters are mounted on ve"rtical shafts The capstan barrel may be mounted on top of the cablelifter but on larger equipment above 76 rom (3 in.) diameter cable - it is usual to have the capstan barrel mounted on a separate shaft as shown in Fig 2 MOORING EQUIPMENT These are, at the present time, no accepted Classification Society rules for the selection of mooring equipment, the size and type of equipment adopted for a vessel generally being based on past experience However, certain independent authorities and major oil companies have instituted their own investigations into the question of mooring techniques and equipment and a basis for selection of tanker mooring equipment is available Hauling load duties of warping capstans and mooring winches vary between 30-300 kN (3-30 tons) at 0.3-0.6 m/sec (60-120 ft/min) and twice full load is normally provided for recovering light lines The size of wire rope used on mooring winch barrels is limited by the weight of wire manageable by the crew; this is currently accepted as 48 mm (2 in ) diameter maximum The basic problems associated with the use of wire ropes is that they are difficult to handle, they not float and when used in multilayers, due to inadequate spooling, the top tensioned layer cuts down into the underlying layers causing damage In order to counteract this latter problem, a divided barrel can be used so that the wire may be stored in one portion and a single layer of wire transferred to the second portion when tensioned The low density, high breaking strength synthetic rope (polypropylene, nylon, terylene, etc.) offers certain advantages over the wire rope, its one main disadvantage being a tendency to fuse if scrubbed against itself or the barrel These ropes are currently in use with double drum warping equipment and storage reels on tankers and bulk carriers The fitting of synthetic ropes direct to mooring barrels is also currently being tested in practice, apparently with some success Mooring winches are currently manufactured with steam, electric or hydraulic drives The two basic types are described below 2.1 NON-AUTOMATIC MOORING WINCHES These winches provide the facility for tensioning the hauling wire up to the stalling load of the winch, usually 1.5 time the hauling load; thereafter the load is held by the prime mover brake or preferably by the barrel brake with the barrel de-clutched The winch cannot payout wire unless the brake is overhauled (when the rope tension overcomes the braking torque) or recover wire unless manually operated Thus wire will become slack during service unless constantly attended, because of tidal variations, loading/unloading, etc 2.2 AUTOMATIC MOORING WINCHES These winches provide the maRual control facilities of the non-automatic winches However, in addition they incorporate a control feature such that, in the "automatic" setting, the winch may be overhauled and wire is paid off the barrel at a predetermined maximum tension In addition, wire is recovered at a lower tension should it tend to become slack Thus there is a certain range of Armature voltage control may be readily obtained by controlled rectification of the ship's a.c supply, using a thyristor bridge Up to 10 hp a single-phase bridge is more economical but for the larger powers associated with deck equipment a three-phase bridge would be used to balance the load on all three supply lines Such a bridge arrangement is shown in Figure 39 Since each arm of the bridge is "fired" in sequence it follows that the ripple frequency will be six times that of the supply frequency The inductance of the armature winding is better able to smooth out this higher frequency voltage ripple The resulting more nearly constant current improves the commutation of the motor The wave form of the output from such a bridge is shown in Figure 40 If the motor is designed for a voltage which is not compatible with the rectified ship's supply voltage, or if isolation is required, a transformer can be used Neutral connection to a three-phase rectifier system may be used, reducing the number of thyristors and at the same time halving the ripple frequency This basic circuit and the resultant waveform are shown in Figures 41 and 42 respectively The thyristors are efficient control elements but have a small voltage drop when conducting which generates heat A thyristor conveying a mean current of 100 A dissipates some 120-150 Wand it is common for thyristors of more than a few amps rating to be clamped to a cooling fin o{heat sink A special grease of high thermal conductivity is smeared on the mating surfaces to ensure intimate contact To improve clarity, the devices necessary to protect the thyristors from surges are not shown on the above diagrams Consisting of resistances or capacitors or semiconductor avalanche voltage limiters, voltage dependent resistors, they will be found close to the thyristor When necessary other protective devices such as air-cored chokes can limit rate of current rise The controlled rectification from this application of thyristors means that, with a given motor connection, torque will only be produced in one direction To provide a reversal of torque it is necessary to reverse either the armature or field connections or to provide a second thyristor bridge connected in the reverse sense These alternatives are shown in Figures 43-45, respectively The armature reversal scheme is the simplest as it is easy to turn off the current, change over the direction-selecting contactors, and re-advance the firing pulses This takes a fraction of a second and even for hoist motions on full load there is no perceptible loss of control when the motor torque is removed, due to the inertia of the motor armature which is in effect multiplied by the square of the overall gear ratio Field reversal can also be performed rapidly by using field forcing techniques and without switching Circuits similar to that used for Ward Leonard generator field control are used (see section 4.2.2.4.1.) As the field strength is reduced, the motor back emf is reduced and the armature current will increase rapidly to short-circuit proportions To prevent this the armature supply rectifier control 42 system is provided with an automatic current limit control which reduces the applied voltage as the motor back emf falls The use of reverse-connected rectifier bridges is in some respects simpler but care has to be taken in the design of the control logic to ensure that the opposing rectifiers can never be fired simultaneously as this would short circuit the supply For safety, especially on hoist drives, it is good practice to initiate the brake application when an armature or field reversing sequence is in progress The brake is then re-energised (released) when the armature circuit is restored or when the field is again above the minimum working value This may be done simply by switch interlocks on the reversing contactors and a current-sensitive field-failure relay, respectively In practice the decay in the magnetic flux of the brake release magnet takes a finite time and the brake does not "drop on" during a normal torque reversing sequence A similar provision can be made in the third system but this is a more complex arrangement and reference should be made to the manufacturers' service manual The design possibilities with electronic control are virtually unlimited and it is common practice to make some of the features automatic One such, already mentioned, is the current-limit system This can be made to depend on the selected speed so that higher currents are permitted at stall to aid the initial acceleration Again, the light-hook speed may be introduced automatically depending on load; or may be limited to the control range when top speed is demanded This is achieved by allowing the motor field to weaken when the armature current falls below a selected value; or, in the latter case, by linking the field weakening system to the last fraction of the armature voltage control, say from 80 to 100% ofvoltage In this case, as the field weakens with rising voltage and a partial load, the current builds up and will eventually initiate the current limit control which reduces armature voltage and so stabilises the field current This system is better for high-duty applications as the average armature current, and hence motor heating, are reduced when operating below base speed 45 MAINTENANCE 1~.1 General The objective of a maintenance schedule is to keep the equipment in perfect working order and as near to its original condition as possible The manufacturers of deck machinery indicate in their manuals the appropriate periods at which, in average conditions, attention to various working parts is needed Conditions vary considerably between ships, types of cargo, ports of call and climates and the necessary intervals between service will vary accordingly Equipment on deck which is used infrequently is particularly prone to damage by corrosion of exposed working parts A few minutes devoted to operating the equipment and greasing working parts when the lubricant has been washed out by spray or rain can save many hours or even days needed for stripping and freeing parts which have seized At suitable intervals intermediate inspection should be carried out to ensure that any change in condition is noted and action taken in good time Particular aJtention is necesSllry after storms to, ensu.re that w;ater has not pel,letra ted any critical parts such as controllers,' panels, motors and geai:cases: Any affected equipment must be dried out before corrosion damage becomes a problem Good preventative maintenance will greatly reduce the need for fault finding and the latter is handled with greater efficiency the more familiar the engineer is with his equipment The author makes no apology for stating what is obvious common sense in this introduction to the subject as these elementary precautions are too frequently ignored, even on new ships Once a period of neglect has been allowed it becomes a major effort to bring all the equipment back to standard This section will be devoted to maintenance and fault rmding on electrical control gear and machinery, as the main points on steam and hydraulic equipment are deal with elsewhere in this series 5.2 Motor Bearings The bearings of electric motors are nearly all of the ball or roller type and are normally grease-lubricated and sealed The lubrication requirements of such bearings are quite modest, depending on running time and temperature The normal requirement is two strokes of a grease gun every six months Excessive amounts or too frequent application will eventually fill the voids of the bearing raceway and the resulting churning action will cause the bearing to overheat, destroying the grease and damaging the seals The same problem can occur when replacement bearings are fitted if the housing is packed with too much grease on assembly Some motors are fitted with a lip seal on the outside of the bearing and a labyrinth seal on the inner side to allow excessive grease to escape and in this type of assembly excess grease will build up inside the machine where it will be a nuisance 46 5.3 Squirrel cage induction motors The simplest motor to maintain is the squirrel cage motor In normal use this will only need periodic greasing of the bearings and checks to ensure that the anticondensation heater is operating The insulation resistance of the main windings should be measured and logged at least once a year and preferably at six monthly intervals The insulation should also be checked if evidence of condensation or water ingress is found on inspection Depending on a number of factors the insulation resistance will vary from several megohms to several hundred megohms between line connections and earth If the value has fallen to one megohm or less the presence of moisture in the winding is likely and drying out should be put in hand Methods vary, depending on the urgency, from ventilating the motor casing forcibly with a hot air gun to placing lamps inside the casing and leaving a small opening for the warm, moist air to escape When resealing the motor gasket, jointing should be replaced where damaged to restore a watertight enclosure and minirnise further problems If the in~laiion resistance is less· than 250,000 ohms the motor should not be started until the figure has risen appreciably, otherwise there will be a fair risk of insulation breakdown and the winding will be burned out or seriously damaged When the winding is found to be virtually short-circuited to the motor frame and the insulation resistance does not recover on drying out, water has fully penetrated the insulation and an earth fault path has been formed The motor will then require rewinding, either by the original manufacturer or a competent repair specialist 5.4 Wound rotor induction motors The general remarks in the previous section apply also to this type of motor The rotor winding in this case is fully insulated from the rotor and the ends of the windings are connected to sliprings mounted on the shaft The insulation of this winding must be checked in the same manner as the stator Current is collected from the slipring by carbon and copper composition The condition of the brushes and rings should be checked periodically to ensure that they make full contact The brush guidance system and pressure springs should also be checked to ensure they are free and provide adequate contact pressure When brushes are worn they should be replaced before the springs or support arms come into contact with the sliprings New brushes must be bedded to obtain a full arc of contact This is done simply by placing a strip of glasspaper (do not use emery or other metal abrasive tapes) in tight contact with the slip ring and the abrasive face in contact with the new brush The strip is slid back and forth around the circumfenmce of the slipring until the full face of the brush conforms to the curvature of the slipring Carbon dust produced by this process should be collected by a cloth or by vacuum Blowing out should be avoided as it is inevitable that some of the carbon will lodge in crevices in the windings and may contribute to failure at a later date 47 5.5 Direct current motors Direct current motors require regular inspection and cleaning 'to ensure that the commutator is kept in good condition The brushes are softer than those used on slipring motors and are available in a variety of graphite compositions The grade should not be changed, without reference to the motor manufacturer, as it will have been chosen for the specific machine application The condition of the commutator can generally be assessed by its colour and surface The colour should be a dark coppery brown with a smooth polished surface The edges of the bars on the commutator should be inspected to check that they are not rubbing over or eroding away', The small gap between the bars where the mica insulation has been undercut should be clean and free of particles After a long period of service the copper will wear down and the mica start to protrude above the surface When this happens the face of the brush will be scored· and circumferential marks will appear The mica must then be cut back to renew a clearance depth of approximately lmm, If the commutator is bright and shining this could be due to too hard a grade of brush or to an extended period of running on no load Excessive blackening and rapid wear of the brushes could be caused by contamination of the brushes or commutator by grease or oil All traces of grease and oil must then be removed before the brushes are replaced and the motor returned to service On some machines dark patterns appear on the surface of the commutator and each tells an experienced observer something of the machine's performance Dark edges on every second or third commutator bar are not generally of any concern unless they are accompanied by erosion or burning away at the edge of the bar or of the brushes When such damage is found check the equipment to the manufacturers recommendations and look for faults such as excessive speed (indicating inadequate field strength) or incorrect speeds forward and reverse drive (indicating incorrect brush position) The appropriate action should then be taken to avoid further damage Other marking should not require action but it is wise to observe the commutator when the motor is working on load Ideally no sparking should be visible between brush and commutator; but minor sparking, just observable in dim light at full load, may be ignored Bright sparks clearly visible in good light may show that action is needed and if no cause can be found the manufacturer should be consulted In replacing brushes the correct grade should be used and bedded down as described for the slipring motor The brushes should be a good fit, yet slide easily in the holder The holders and brush arm should be secure and care must be taken when replacing brushes that the brush holder settings are not disturbed The field system of the d.c motor ngrmally consists of main poles and interpoles, each type wound with coils of wire to suit their respective current ratings The interpole coil carries the armature current and is arranged to counteract the demagnetising effect of this current The series and separate shunt w.indings are fitted to the main pole and may be wound and insulated as separate coils or together as a compound coil 48 The field coils normally have a very high insulation resistance to the frame or earth If it is found low, the coils should be examined for signs of moisture or of abrasion between coil and pole pieces If the insulation resistance of the armature circuit, including series and interpole coils, is low the location of the leak should be established by selectively retesting the circuit in parts The most common cause of low insulation resistance is mois'ture, followed by contamination by ca,rbondust and water-borne residues A low insulation' value can often be restored to an acceptable level by cleaning and drying out the machines in situ Very low insulation resistances indicate that matters have probably progressed too far and repair work is necessary 5.6 Ward Leonard set If the generator runs in reverse, the negative series winding becomes positive and a very large current will be generated in the d.c circuit This can be sufficient to prevent the a.c drive motor reaching running speed and could damage the rotor by over-heating in a minute or less; also, the starter will have to interrupt the full starting current when it is tripped When two generating sets are driven by a common ac motor at least one, if not two, drive couplings will be used These should be checked for wear and backlash as well as alignment Both misalignment and wear can cause vibration in operation Remedial action is then necessary to prevent further damage to bearings and shafts 5.7 Brakes On hoisting machinery in particular a brake is provided for safety Such brakes fail safe, in that they are applied by a spring and electrically released The most common is the disc type, mounted integral with the motor assembly, as this form is easily protected and made watertight A typical brake arrangement is shown in Figure 46 The essential features are the coaxial magnetic assembly and the moving armature plate/friction member which is pushed by springs against the friction material carried on the motor shaft The friction material is permitted some axial movement so that a second face can come into contact with the outer cover, effectively doubling the torque The brake shown has frictional material in the form of plugs which can slide axially in pockets in the rim of the carrier plate which is keyed to the motor shaft An alternative arrangement has frictional material riveted to the plate; which is itself able to move axially on a sliding hub, keyed to the motor shaft The majority of brakes of this type not require adjustment as they are designed to develop the required torque over the full range of wear permitted in the working life of the friction material The rate of wear should be checked at regular intervals with reference to the manufacturers limitations When the friction material has to be replaced the whole of the lining should be replaced and the brake housing cleaned out before 49 reassembly Asbestos is a major constituent of many friction materials and due care must be taken to avoid the inhalation or ingestion of any dust To avoid the hazard of a load remaining suspended in the event of power failure, it is usual to provide means for releasing the brake manually in a controlled manner This may be done by a lever or more simply by "push-off' screws Such mechanisms must be kept free from contamination and lubricated Push-off screws must have the spacing collars replaced before they are locked in place after use Modern electrically driven deck machinery provides most of the duty braking electrically and the mechanical, brake function is mainly in holding or emergency stopping In normal operations the brake may become hot to touch but if it shows signs of excessive heat, such as paint blistering, the machine should be stopped and the cause investigated, as prolonged overheating will distort and damage it 5.8 Cables and terminations Cables not normally require maintenance but it is good practice to examine them periodically Points to check are the condition of the covering, where accessible, with particular attention to support clips and points of entry to ducts and through bulkheads The ever present vibration on a ship can rapidly chafe through the protective covering if there is relative movement at a point of support Cable runs should allow for expansion and contraction due to temperature changes and be secured or protected where they change direction Terminals should be checked at every major inspection and tightened if necessary Power connections may overheat if they become loose and any found discoloured or corroded should be opened and cleaned before retightening Crimped cable terminations are being used widely now as they offer a convenient and reliable connection method It is however vitally important to ensure that the correct size of termination is used to match the conductor and that the correct compression tool is used in good condition Joints made with worn or incorrectly adjusted tools or with the plier type of hand tool may not be correctly indented and cause trouble in time through overheating or intermittent connection 5.9 Controls The controls of deck machinery may be located on the machine, in a separate pedestal nearby, or at some remote position convenient for the operator As for all deck-mounted gear the environmental conditions are severe and condensation and salt water corrosion can cause trouble if the units are not maintained Condensation can be kept under control by means of low-power heaters These should be checked periodically to make sure they are working and switched on at all times when the equipment is not in use Controller spindles, switch shafts and push button sets should be regularly lubricated and tested for freedom of movement Any sign of stiffness should be investigated and rectified before the parts seize This, for obvious reasons, also applies to limit switches, trip bars and emergency stop stations 51 The working parts of electrical control systems are normally grouped together on a panel or framework in a protective enclosure which prevents accidental contact with live conductors and the entry of contaminants A method of isolating the electrical supply locally or of locking a remote isolator is usually provided, for the safety of maintenance staff It is good practice to have an interlock so that the enclosure can not be opened unless the isolator is open For the convenience of experienced electrical maintenance staff it is usually possible to re-energise the equipment when the enclosure is open so that the functioning sequence of relay and contactor operation can be observed No panel should ever be left unattended when open and energised Both ventilated and sealed control panels are advantageously provided with an anti-condensation heater which should be checked periodically 5.9.1 Open contactor The open or "clapper" type of contactor is still widely used, particularly for the control of d.c Its construction permits ready inspection of contacts, arcing tip, shields, pivots and magnet assemblies A periodic examination of these items is needed to monitor wear All assembly screws should be tight and the moving parts free The main pivots should be lubricated sparingly Every three months (or at shorter intervals if in frequent service) the contacts should be examined Main contacts should be clean and bright if copper to copper contact is used They should be cleaned to remove arc products, dirt, etc Badly burned copper contacts can sometimes be restored by filing the profile back to shape, but only where at least three quarters of the contact line can be regained by this method When this is done the removal of metal reduces the contact pressure so that the remaining pressure must be checked to ensure it is adequate On multipole contactors the line up of the contacts should be adjusted to ensure that all poles make and break contact simultaneously Arc tips, which may be of copper or carbon, should be replaced when eroded and the connections and adjustment checked to ensure that the tip makes contact first and breaks contact last Silver·faced contacts should not be filed at any time Light-current silver faced auxiliary contacts can be cleaned sufficiently by drawing a strip of paper between the closed faces if a 'spatula' type relay contact cleaner is not available The magnet assembly should be properly aligned and the faces clean, any contamination should be removed and the faces wiped with an oily cloth Magnets energised by alternating current are fitted with a copper shading ring at the pole face to prevent chatter Damaged shading rings should be replaced if the magnet is noisy in operation, after first checking that the magnet is free to close fully If this type of contactor is fitted with arc shields or magnetic blow-out devices it should never be operated when these items are not correctly in position The magnet coil should be secure to prevent damage by vibration tions should also be secure 52 Coil connec- 5.9.2 Block contactors This type of contactor is increasingly used for switching three-phase a.c pOWf;r as they are compact and competitively priced The working parts slide in guides within the assembly and double·break silver-faced contacts are commonly used Maintenance is simple, requiring only a periodic inspection of the contacts and sliding parts to check for wear Contacts, being silver-faced, should not be dressed Even though black and pitted, they remain serviceable until the silver has been eroded away, when the complete contact set should be replaced Auxiliary contacts breaking very low voltages and currents may not be selfcleaning These may have to be burnished if found to have a measureable contact resistance Plastic guides for the sliding parts not normally require lubrication but should be kept clear of all dust and abrasive contaminants Any springs found damaged or corroded should be replaced 5.9.3 Relays Open relays should be treated in a similar manner to open contactors although the controlled currents are generally smaller and special alloy contact faces are used Such contacts should not normally be dressed with a file or abrasive unless the manufacturers' instruction book permits this Smaller relays are now usually enclosed in a protective cover No action is required to maintain such units and they are normally replaced as a unit Security of circuit connections should always be checked before discarding a relay as faulty On special purpose relays, such as voltage or load current sensing devices, slugged sequence relays and current lockouts, maintenance is normally quite nominal but, with time and wear, set points can vary and adjustment will be required at infrequent intervals All the diverse types of relay cannot be discussed here: equipment manuals should be consulted for the adjustment procedures which must be observed carefully to regain the required settings as some properties of relays are interrelated For example, adjustment of the "pick up" setting will affect the "drop ofP' value and further correction will be needed which will in turn affect the pick-up value Such step by step adjustments can be tedious but are necessary to obtain a reliable and consistent setting Overload relays in common use are thermal or magnetic The thermal type is based on the distortion of a bimetalic strip when heated by a small resistance which carries the load current For heavy ac a current transformer is used to feed the heater resistance and for large dc a shunt With multipole overload relays it is possible to detect load imbalance in the circuits by the differential movement of the bimetallic strips and this feature is sometimes used to advantage, for example in the protection of an induction motor from single-phase operation 53 In recent years a new type of thermal overload protection has been introduced which relies on the change in the resistance value of a semi-conductor Such a 'Thermistor' can be made to undergo a large change in its resistance value at the limiting temperature for safe working One is embedded in each phase winding of the motor but insulated from the winding The thermistors are connected in series with a relay which drops out when they undergo the resistance change, tripping the main supply contactor Thermal overload devices require no maintenance apart from ensuring that connections are secure It is not normally practical to attempt repairs if the units are damaged except for replacement of heaters Faulty units should be replaced with new ones Magnetic overload relays are set so that the armature will not be attracted by safe currents Overload currents increase the attraction and the armature will start to move To prevent instantaneous operation at this point, a drag is applied to the armature by means such as a piston in an oil-filled dashpot The delay obtained is inversely proportional to the excess attractive force At some point in the travel of the armature the piston leaves the working section of the dashpot and the armature completes its motion, rapidly opening the trip or operating contacts quickly to prevent contact burn in the final portion of the movement The oil used in dashpots can become depleted or dirty and may have to be replaced This oil is formulated with a precise viscosity value for each application which does not vary significantly with temperature Only the special oil recommended by the manufacturers may be used Normal lubricating oils are totally unsuitable and may render the overload inoperative, risking burn-out of the protected equipment Timing relays are used to limit the maximum speed at which a control sequence may be executed They may be mechanical, such as an escapement or drag-cup mechanism; pneumatic, using a piston or diaphragm and orifice; or electrical, using a resistor and capacitor The timing mechanism is usually sealed to protect the components The timing element or the whole unit should be replaced if the timer fails to operate or cannot be adjusted to the required time by the means provided 5.9.4 Resistances Resistances used for power regulation on marine equipment are usually of a rustless, unbreakable type which means that the element is made of a ductile, corrosion-resisting alloy with a low thermal coefficient of resistance Maintenance requirements are low but the units should be inspected periodically to ensure that the mountings and clampings are secure Terminations should be checked for tightness If they are locally discoloured the cable should be removed, the contact surfaces cleaned and the joint remade and tightened If the cable is damaged by heat the insulation may have to be cut back and the end re-taped with heat-resisting tapes 54 If power re.sistors are fitted with forced air-cooling the fan motor will require regular attention Resistors for field and brake control may be quite large, carrying several amps Maintenance is again minimal, requiring only inspection of terminations and mountings for tightness Any resistor showing signs of overheating and discolouration should be investigated Bad connections can cause local damage at the terminals and with some type of resistance it is possible to unwind one turn of wire and remake the connection if no spare is available Small resistances should be replaced with a similar unit of equal ohmic value and wattage rating as repair is not possible 5.9.5 Rectifiers Rectifiers used in control equipment only require cleaning at infrequent intervals and a periodic check of the security of connections Care is required to protect the rectifier if insulation tests are being made with a high-voltage tester such as a "Megger" as the voltage may be sufficient to destroy the rectifier The a.c; and d.c terminals should be bound with a,corilinon conducting wire, effectively shorting out the rectifier for such tests This binding wire should be clearly tagged to ensure that it is seen and removed before power is restored It should also be noted that bell sets and buzzers can generate dangerously high voltage pulses Rectifiers are not subject to partial failure If faulty, they are usually open circuit or, more likely, short circuited The arms of a rectifier bridge may be checked readily by using a multimeter with an ohms range and at least a 3V internal battery The resistance in the conducting direction should be appreciably lower than in reverse A healthy rectifier will always show a measurable forward resistance as 0.75-1.5 V is needed to turn the device on The terminal polarity of a multimeter is usually reversed when operating on the ohms range 5.9.6 Thyristor equipment Electronic control gear has no working parts to be maintained in the control panel but the system may employ auxiliary circuits with contactors and relays which require periodic attention as already described The thyristor stack assembly should be kept clean and connections and mountings checked for tightness during routine maintenance Any printed circuit control boards should also be kept clean and fully inserted into the connection socket The circuit side of the control boards should be inspected for cleanliness and absence of corrosion and, if necessary, cleaned and varnished to restore the protection Adjustable components and contacts should be protected from the varnish Megger sets, bells and buzzers must not be used on thyristor circuits to cheCk wiring as the high voltages from these units can easily destroy the thyristors 55 as well as the low voltage transistors Instead a multimeter or a special electronic circuit continuity tester should be used to ensure that no damage can be done If forced cooling is used to ventilate the thyristor cooling fins the fan and motor will require periodic maintenance FAULT FINDING There is unfortunately no easy road in fault finding on defective equipment To be successful in this task it is necessary to have a knowledge of the correct functioning of the equipment The location of a fault is a logical, step by step, process of elimination A useful aid in this is a written sequence of tests progressing from energisation through start-up to operational control By this means it is possible to determine quickly the point in the sequence where the fault appears and, by observation and deduction locate the problem in a definite part of the system A reliable and factual report from the operator at the time of failure can also be a valuable aid as it may give information on probable causes or earlier symptoms which will assist in the deductive process Fault finding charts can be prepared or obtained from the manufacturers of equipment but these are only of real value on complex equipment where many circuits interact with one another Generally ship's deck equipment employs relatively simple control schemes and the method of elimination described above is the quickest method Electronic equipment may be provided with self-checking circuits or the manufacturer may specify a routine for checking that the controls are functioning correctly As a general rule, even with electronic controls, it is best to suspect a simple fault such as a blown fuse, broken connection or jammed limit switch in the first instance These simple faults can usually be eliminated very quickly All external circuits should be checked before disconnecting sections within the control panel A visual inspection for damage due to overheating and for broken or loose connections should also be made before disconnecting or removing any suspect component Failure of a mechanical or pneumatic timing device can be checked with the power off by operating the assembly manually Electrical timing circuit faults can only be checked when energised Whilst detailed knowledge and operating experience of a control system is essential for speedy fault finding -by 'intuition' a calm and orderly, logical approach will generally produce results but take slightly longer Disorganised 'check-and-try' methods must be avoided as such short cuts almost invariably produce some additonal defects and make the task more difficult and time consuming 56 ... Marine Engineers ISBN: 900976 78 Printed by Hobbs the Printers in the UK CONTENTS 1.1 1 .2 1.3 2. 1 2. 2 3.1 3.1.1 3.1 .2 3 .2 3.3 3.3.1 3.3 .2 3.3.3 4.1 4 .2 4 .2. 1 4 .2. 2 4 .2. 2.1 4 .2. 2 .2 4 .2. 2.3 4 .2. 2.4... 3.3 .2 3.3.3 4.1 4 .2 4 .2. 1 4 .2. 2 4 .2. 2.1 4 .2. 2 .2 4 .2. 2.3 4 .2. 2.4 4 .2. 2.4.1 4 .2. 2.4 .2 4 .2. 2.4.3 5.1 5 .2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.9.1 5.9 .2 5.9.3 5.9.4 5.9.5 5.9.6 Anchor Handling Equipment Windlasses... Page I 2 4 6 7 10 10 10 13 17 17 18 18 24 24 27 30 35 37 39 39 46 46 46 47 47 48 49 49 51 51 52 53 53 54 55 55 57 LIST FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG FIG 123 45678910 11 12 13