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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…. Anchor Handling.
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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…
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 • 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.
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.
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 pressureAtmospheric 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 • 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
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 popularin the recent times
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. • 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.
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 whereD = DisplacementB = beamh = Freeboard + height of deckhouses over B/4 wideA = 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 • 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 • 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
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 • 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 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%. • Rack and pinion drive • Chain drive • Roll-up-Roll are normally used for operation
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/pVariable frequency drive controllers are solid stateelectronic 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.
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 Schematic Of Launch
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.
