Marine Machinery 7 E Part 11 docx

390 Heating, ventilation and air conditioning Table 12.3 Schedule of air changes Air changes I hour Spaces served Deck Wheeihouse Nav. Bridge W.C. Captains, chief officer's and deck officers' accommodation Radio office Motor gen. room, gyro and electronics room Bridge Officers' toilets and drying room Baggage room Officers' smoke room and bar, games room Chief engineer's and engineers' accommodation, pilot and owners representatives Laundry Boat Switchboard room, telephone exchange Engineers' toilets and change room, pantry, drying room, equipment locker Lockers Cadets, catering officer, PO's and junior engineers Cargo control room, dining salons, crew's mess room, crew's smoke room Poop Hospital Medical locker Galley Cadets', engineers', catering officer's and PO's toilets Games room Crew accommodation Laundry Motor room Bedding, beer, dry provision and bonded and equipment stores Upper Crew toilets, change room, laundry, drying rooms Handling space Supply 6 _ 9 12 15/30* _ — 12 9 6 30* _ — 9 12 12 __ 20* — 12 9 6 30* 10* _ - Exhaust _ 15 _ _ 15/30 15 10 _ _ 15 30 15 10 _ _ 0.14mVst 10 40 15 _ _ 15 30 _ 15 12.5 * Air at atmospheric temperature t Through WC and bathroom. Heating, ventilation and air conditioning 391 conditioners, to operate on 440 v, 3-phase, 60 Hz supply. Power consumption 1.2kW per unit. At least 7 litres/s of fresh air per occupant of room should be taken from machinery space system. The shipbuilder should pipe condenser cooling water from ship's services. Erosion of condenser piping may be prevented by fitting a 'Constaflo' control valve in each unit to limit flow to 0.15 litre/s per unit. This proposal is exclusive of heating. The shipbuilder should supply and fit suitable bases for units, provide switches, wire up to motors and switches, and supply and fit cooling water drain piping and fittings. Installation serving the cargo pump room The cargo pump room is ventilated by two axial flow exhaust fans each to extract 1.4 mVs against 3.1 mbar static, requiring a total of 2.25 kW. The fans should be of split case bevel gear driven type enabling the fan motor to be mounted in the adjacent engine room. Motor and controller spare gear must be provided. Air is extracted from two low level points through wire mesh grids fitted on galvanized steel ducting. The shipbuilder must supply and fit air outlet jalousies with hinged water tight covers, and natural ventilation to operate in conjunction with the mechanical system. Further reading Merchant Shipping Notice No. Mil 15 Contamination of Ships' Air Conditioning Systems by Legionella Bacteria. 13 Deck machinery and cargo equipment The operation of mooring a vessel has traditionally required the attendance of a large number of deck crew fore and aft. Supervision of the moorings was also necessary to maintain correct tension through changes due to the tides and the loading or unloading of cargo. The installation of constant tension mooring winches, which maintain tension in ropes through any rise and fall, has removed the need for constant attendance and equipment is available for tying up which is designed for operation by as few as two men. Large container ships may have four mooring winches on the after deck; each of the seif-tensioning type with its own rope drum. Controls are duplicated and are situated at each side of the vessel, giving a clear view of the operation. Mooring ropes are paid out directly from the drums as they are hauled by the heaving lines from the quay. With the loop in place on the bollard, the capstan is set on auto-tension after slack is taken up and the ship is correctly moored. A common arrangement forward is for two similar winches plus rope drums for auto-tensioning on each windlass. The introduction of steel hatchcovers not only speeded up the operation of opening and closing the covers but also reduced the number of personnel required for the task. Rolling and folding covers may be operated by a pull wire or hydraulically. Covers for large container ships may be lifted bodily by crane and there are now hatchcoverless container ships in service. Cargo handling may be by winches and derricks or cranes. Some geared bulk carriers have overhead cranes arranged to travel on rails. Most deck machinery is idle during much of its life while the ship is at sea. In port, cargo equipment will be in use for one or more days but the machinery for anchoring and mooring is used for a very limited time. Deck machinery with a restricted and intermittent duty may be designed with drives with a rating limited from 30 minutes to one hour. Despite long periods of idleness, often in severe weather conditions, machinery must operate immediately, when required. Cooling vents, open when machinery is working, must be closed for the sea passage. It is essential that deck machinery should require minimum maintenance. Totally enclosed equipment with oil bath lubrication for gears and bearings is now standard but maintenance cannot be completely eliminated and routine checking and greasing should be carried out on a planned basis. There are many instances where remote or centralized control is of great advantage, for example, the facility for letting go anchors from the bridge Deck machinery and cargo equipment 393 under emergency conditions; the use of shipside controllers with mooring winches; or the central control positions required for the multi-winch slewing derrick system. The machinery on the deck of an oil tanker is limited to that used for anchor handling and mooring plus pumproorn fans and equipment for handling the gangway and stores. Power was universally provided in the past by steam. Hydraulic equipment is now common, sometimes with air motors for gangway duties. The availability of safe electrical equipment means that electric motor drives can be used where appropriate. Liquefied gas carriers and product or chemical tankers have similar deck machinery installations but the drive motor for deepwell pumps may be an induction motor of the increased or enhanced (Ex e) safety type. Either electric or hydraulic drives are installed for the deck machinery of dry cargo vessels, Electric drives Electric motors on vulnerable deck areas may be protected against ingress of water by being totally enclosed in a watertight casing. Vents are provided on some winches, which must be opened when the motor is operating in port. The direct current (d.c.) motor, although it is relatively costly and requires regular brush gear maintenance, is still used for deck machinery because it has a full speed range with good torque at any speed. The control of d.c. motors by contactor-switched armature resistances, common in the days when ships' electrical supplies were d.c., has long been replaced by a variety of Ward-Leonard type systems which give a better, more positive regulation particularly for controlled lowering of loads. The Ward-Leonard generator is normally driven by an a.c. motor. An important feature of the d.c. drive is its efficiency, particularly in comparison with a.c. drives, when operating at speeds in the lower portion of the working range. The d.c. motor is the only electric drive at present in production which can be designed to operate in a stalled condition continuously against its full rate torque and this feature is used for automatic mooring winches of the 'live motor' type. The majority of d.c. winch motors develop full output at speeds of the order of 500 rev/min and where necessary are arranged to run up to two to four times this speed for light line duties. Windlass motors on the other hand do not normally operate with a run up in excess of 2 : 1 and usually have a full load working speed of the order of 1000 rev/min. Direct current motors may also be controlled by static thyristor converters which convert the a.c. supply into a variable d.c. voltage of the required magnitude for any required armature speed. These converters must be of a type capable of controlled rectification and inversion with bi-directional current flow if full control is to be obtained (Figure 13.1). Alternating current induction motors, of either the wound rotor or of the cage type are also in common use. With these the speed may be changed by 394 Deck machinery and cargo equipment Figure 13.1 Load/speed characteristic of Ward-Leonard thyhstor controlled winch. See Figure 13.2 for conversions to m/sec (Clarke, Chapman Ltd) means of pole changing connections and in the case of the wound rotor induction motor, also by changing the value of the outside resistance connected in the rotor circuit. The pole change method involves the switching of high currents at medium voltage in several lines simultaneously, requiring the use of multi-pole contactors. The pole change speed control method offers a choice of perhaps three discrete speeds such as 0.65, 0.325 and 0.1025 m/s corresponding to 4, 8 and 24 pole operation. The wound rotor motor is flexible when hoisting a load, because the starting resistances can be reintroduced into the rotor circuit and the load will cause the motor to slip. The slip gives a range between the speeds dictated by the pole arrangement. As with resistance controlled d.c. motors, difficulty is experienced when providing speed control of an overhauling load, i.e. lowering a suspended load. The disadvantages must be balanced against lower cost, particularly of the cage type induction motor, in comparison with the more flexible d.c. motor. Typical performance curves are shown in Figure 13.2. Another form of induction motor control system is based on the relationship between output torque and applied voltage, the torque being proportional to the voltage squared. The controller takes the form of a three-phase series regulator with an arm in each supply line to the motor. A stable drive system Deck machinery and cargo equipment 395 Figure 13.2 Performance curves of a 3 tonne winch. AC pole-changing 'cage' motor. (Clarke, Chapman Ltd) can only be achieved by this means if a closed loop servo control system is used in conjunction with a very fast acting regulator which automatically adjusts the output torque to suit the load demand at the set speed. Control of an overhauling load is made possible by using injection braking techniques. A combined system employing both these control principles can provide full control requirements for all deck machinery. The a.c. drives described operate at the supply frequency and consequently rapid heating of the motor will occur if the drive is stalled when energized. The majority of a.c. motors on deck machinery run at a maximum speed corresponding to the 4 pole synchronous speed of 1800 rev/min on a 60 Hz supply. These speeds are similar to the maximum speeds used with d.c. drives and the bearings and shaft details tend to be much the same. The motor bearings are normally grease lubricated. However, where the motor is flange mounted on an oil bath gearcase, the driving end bearing is open to the gearcase oil and grease lubrication is not required. 396 Deck machinery and cargo equipment Hydraulic systems Hydraulic systems provide a means of distributing power and of obtaining it from a constant speed and constant direction drive such as an a.c. electric motor. The oil pressure can be used to provide variable speed drives through hydraulic motors and power for actuating devices. Hydraulic power is used extensively for deck machinery and remote control of valves. Hydraulic systems The three essential components for a hydraulic circuit, are the hydraulic fluid held in a reservoir tank, a pump to force the liquid through the system and a motor or cylinder actuator to convert the energy of the moving liquid into a working rotary or linear mechanical force. Valves to control liquid flow and pressure are required by some systems. Hydraulic fluid Water was the original hydraulic fluid and is still used for heavy duty such as operation of lock gates or moving bridges. The disadvantages with water are that it promotes rusting and other forms of corrosion, it is not a good lubricant and it has a limited temperature range. Hydraulic oils may be straight mineral or special additive oils. Properties of these, enhanced by additives, include oxidation stability, film strength, rust prevention, foam resistance, demulsibility and anti-wear characteristics to enable the fluid to stand up to the higher operating temperatures and pressures of modern systems. Pour point depressants are used to prevent freezing in low temperature conditions. Other fluids used in hydraulic systems may be synthetics or emulsions. Emulsions have been used in systems such as the telemotor, where force is applied and received by pistons. Oils are preferred for systems using rotating pumps and motors, where good lubrication is essential. In an emergency where short term expediency is the criterion, any thin oil could be used in a system. Deterioration of hydraulic oils Hydraulic fluids which are basically mineral oils, will degenerate very slowly over time due to oxidation. The factors which encourage oxidation are the heating and agitation of the oil in the presence of air and metal, particularly copper. The process of oxidation is accelerated by overheating and also by contamination with products of corrosion or the presence of metal wear particles. Oxidation products, both soluble and insoluble, increase the oil's viscosity and cause sludge to be deposited. Oxidation tends to encourage the Deck machinery and cargo equipment 397 formation of emulsions with any water from leakage or condensation. Acidic products of oxidation will cause corrosion in the system. Contamination of oils Water promotes rusting of steel and must be excluded from hydraulic systems. Rust can be detached and when carried around a circuit can cause the jamming of those valves with fine operating clearance, as well as hastening deterioration of the oil. Sea water can enter through the shaft seals of deck machinery and via system coolers. Condensation on the cold surfaces of reservoir tanks which are open to the atmosphere, is a common source of contamination by water. Tanks should not be constructed such that cold hull plating forms one wall Metal wear is inevitable and fine filters are installed to remove these and corrosion particles together with any other grit or dirt that finds its way into the system. Care is necessary with hoses, funnels and oil containers used for filling and topping up reservoir tanks, to ensure that they are clean. Fine metal wear particles can act as abrasives causing further wear. All particles could cause blocking of small passages or the jamming of valves. Systems and components Pump and motor systems are used for powering deck machinery such as winches and windlasses. Pump and actuating cylinders are normally employed for hatch covers. One or more pumps will be used to supply the volume of fluid at the pressure required to operate one or more motors. Pumps may be classified into two groups: 1 those with a fixed delivery when running at a given speed; 2 those with a variable delivery at a given speed. Fixed delivery pumps can have their constant output bypassed via control valves until required or output can be matched to requirements by incorporating a relief/accumulator, then stopping and starting, varying speed, or connecting a variable delivery pump in parallel. Variable delivery pump output can be controlled to give full flow in either direction, and volume output can be varied from maximum down to zero. Fixed delivery pumps Constant output pumps of the gear or lobe type (see Chapter 5) are precision made to provide high pressure with minimum back leakage. The former operate on the principle that as gears revolve, fluid is carried around the outside between the gear teeth and the housing from the suction to the discharge side of the pump. Fluid from the discharge side is prevented from returning to the intake side by the close meshing of the two gears and the small clearances 398 Deck machinery and cargo equipment between the gears and housing. At the discharge side the fluid is discharged partly by centrifugal effect and partly by being forced from between the teeth as they mesh. Gear pumps may be of the conventional kind or of the type with meshing internal and external gears. Lobe pumps (Figure 5.28, p. 173) are a variation of the latter. Axial cylinder pumps can be made to deliver a fixed output by setting the swash plate for continuous full stroke operation. Variable delivery pumps Variable delivery pumps are used in hydraulic installations as the means of regulating pump output to suit demand. Steering gears are controlled directly by varying the pump output and swash plate pumps are used to supply a range of hydraulic deck machinery. Automatic stroke control can be used to adjust the output. Constant delivery pump systems Hydraulic steering gears which are fitted with constant volume or fixed output pumps may have a simple control valve arrangement which either delivers full pump output to the steering gear or bypasses pump output completely. System pressure rises sharply when oil is channelled to the gear. The fixed output pumps of Woodward type hydraulic engine governors, supply to accumulators, which maintain system pressure and hold a reserve of operational oil against demand which may temporarily exceed pump capacity. For general hydraulic systems where the pump delivers a constant volume of oil, speed control of the hydraulic motor can be obtained by delivering the required amount of oil to the motor through a control valve and diverting the remainder through a bypass to the pump suction. The pump discharge pressure is determined by the load. Speed and direction of rotation are controlled by a lever operated balanced spool valve. Unit type of circuit The basic components of a hydraulic system of the Norwinch design are shown in Figure 13.3. The pump in this case is of the vane type which consists of a slightly elliptical case with a cylindrical rotor. The latter has radial slots containing closely fitting rectangular vanes which are forced out against the casing by centrifugal effect and oil pressure. As the rotor turns, the expanding and contracting clearance between it and the casing produces a pumping action. Both mechanical and magnetic filters and a relief valve are provided. The expansion tank contains a reserve of oil. The hydraulic motor is also of the vane type, with vanes mounted in a cylindrical rotor working in a housing Deck machinery and cargo equipment 399 Figure 13,3 Norwinch single hydraulic drive which incorporates two pressure chambers. When the motor is required to exert maximum torque, oil flow from the pump is directed into both chambers. For lighter loads an operating lever is actuated to direct the full flow to only one of the pressure chambers. This system provides two variable speed ranges. The system shown is for mooring winches which are self-tensioning. Pumps for hydraulic installations, such as the one described, run at constant speed and are driven by an electric motor or directly by a prime mover. With the pump running there is a continuous flow of oil through the system whether the motor is in operation or not. When the winch is not in use the oil merely passes through the operating valve, bypassing the hydromotor and returns to the pump. Oil pressure is negligible when the hydromotor is idle, reducing power required to a minimum. Oil in the pipelines to and from the motor always flows in the same direction. At the motor controls the flow direction can be reversed to change the rotation of the winch. Many of the hydraulic systems, fitted to deck machinery are of the 'unit' type, with one pump driving one motor, but there are great advantages to be gained by the use of a ring main system. With the latter type of system, one centrally located hydraulic pump is able to cater for the needs of a number of auxiliaries which can work simultaneously or alternately at varying loads. As the equipment powered from this central pumping installation need not be restricted to deck machinery or to one type of equipment, the system offers considerable savings on capital cost. Variable displacement pump systems The hydraulically operated steering gear with an axial piston (vsg type) or radial piston (Hele-Shaw type) variable delivery pump, is an example of variable displacement pump system. The pump itself controls the liquid flow to [...]... be needed for the radiator in cold weather An emergency pump has an independent diesel drive or some alternative such as an electric motor powered from the emergency generator Pipelines Where steel pipes are used, they are galvanized after bending and welding Their diameter is between 50 mm and 178 mm depending on the size and type of ship Engine room hydrants must have hoses and nozzles for jet and... diesel engine supplied with cooling water from the fire pump a header tank will be provided to ensure that the engine is cooled while the fire pump is being primed The engine could have a closed circuit fresh-water system, with the water being cooled in a radiator It is usual however, to fit an air-cooled diesel engine Where a closed-circuit fresh-water cooled engine is installed anti-freeze may be... 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 of the bevel or spur Deck machinery and cargo equipment 405 reduction gears, and the clutching arrangements required, these gears are often of the open type and are lubricated with open gear compounds Mooring equipment Full load duties of warping... commonly rove to give a level luff — in other words the cable geometry is such that the load is not lifted or lowered by the action of luffing the jib and the luffing motor need therefore only be rated to lift the jib and not the load as well Generally, deck cranes of this type use the "Toplis' three -part reeving system for the hoist rope and the luffing ropes are rove between the jib head and the superstructure... passenger vessels and passenger ferries must have three such pumps The pumps are fitted with non-return valves if they are of the centrifugal type, to prevent loss of water back through open valves when not running A relief valve is necessary in the system if the pumps are capable of raising the pipeline pressure so that it is greater than the design figure With centrifugal pumps the relief valve is... ensure that the jib is supported in the event of hydraulic pressure being lost and an automatic limiting device is incorporated which ensures that maximum radius cannot be exceeded When the jib is to be stowed the operator can override the limiting device In the horizontal stowed position the cylinder rods are fully retracted into the rams where they are protected from the weather Some cranes are mounted... the two pistons it forces them and the helixes apart thus causing rotation through the mating helixes and operation of the hinge Pressure applied to the outside of the pistons creates a torque in the opposite direction Maintenance Hatch cover equipment like the other deck machinery, has to exist in a very hostile environment and the importance of regular maintenance cannot be over-emphasized Drive... from the water level at light draught conditions Ideally they are installed below the waterline to guarantee avoidance of suction problems There have been difficulties in the past with some steering gear located emergency fire pumps when the ship was in the ballast condition If the location of a centrifugal type emergency fire pump is the steering flat then, because of the high suction lift involved,... seal (Figure 13.13) When closed the covers are held on to the seals by a series of peripheral cleats Rollers are arranged on the sides of the covers to facilitate opening and closing To open a single pull cover the securing cleats are first freed and each panel is raised off its compression bars by hydraulic jacks The cover wheels, which are arranged on eccentrics, are rotated through 180° and locked... windlass can expect to fulfil the following: I The windlass cablelifter brakes must be able to control the running anchor and cable when the cablelifter is disconnected from the gearing when letting go' Average cable speeds vary between 5 and 7 m/s during this operation Deck machinery and cargo equipment 401 2 3 The windlass must be able to heave a certain weight of cable at a specified speed This full . rating limited from 30 minutes to one hour. Despite long periods of idleness, often in severe weather conditions, machinery must operate immediately, when required. Cooling vents, open when. can be veered out to the waterline before letting go or heaved in as required. The windlass is in the most vulnerable position so far as exposure to the elements is concerned . precision made to provide high pressure with minimum back leakage. The former operate on the principle that as gears revolve, fluid is carried around the outside between the gear teeth