Masters
Introduction
It is not the intention of this chapter to attempt to turn the Master into a Chief Engineer. It is merely meant to familiarize the seagoing Master with some basic elements of the activities and developments in the subject of marine engineering. Most serving Masters would have at some time in the past experienced the request from the engine room to reduce speed because of a ‘scavange fire’, but the question should then arise, what caused that fire? The fact that the most common cause is worn piston rings begs the question, why is the vessel operating with worn piston rings in the first place and is the function of planned maintenance fulfilling the vessel’s needs?
The Master should be equipped with a basic under- standing of marine engineering and fundamental control systems within his vessel; however, he should not lose the essential assistance and loyalty of his Chief. ‘Ship command’ has been defined as the authority to direct and control a ship, the purpose of which is to carry out the management of all shipboard operations, not least the indirect operation of the vessel’s machinery.
It is generally when things don’t always go according to plan, for one reason or another, that the ship’s Master and Chief Engineer tend to come together. The prob- lems of faulty steering or loss of sea speed are typical examples when the Master could expect feedback. An understanding of terminology, reference to components and the ability to acknowledge one’s own limitations could well go a long way towards identifying the prob- lem and instigating corrective action.
Main engine power
In order for the Master to function as a ship handler it is essential that main engine power remains available. It is appreciated that a vessel without power can be controlled by external forces, supplied by tugs, but under
normal circumstances a Master expects to have full use of main engines. An understanding of the power that is being produced by the engine and the relationship to the actual propeller power being achieved, to provide the ship’s motion, differ considerably.
Definitions
‘Indicated power’ is defined as the actual power devel- oped in the cylinders, derived from the high pressure, hot gases acting on the piston area.
Indicated power is usually measured daily by the engineering officers to ensure satisfactory performance of all cylinders. To obtain the indicated power of an engine cylinder an ‘engine indicator’ is fitted to a test cock on the side of the cylinder. The device produces an indicator diagram and the measured area represents the pressure acting on the piston through its stroke. ‘Shaft power’ is defined as that power available at the engine output shaft, used to drive the propeller or machinery.
NB. Shaft power will always be less than indicated power because of friction and heat losses that occur within the engine.
Shaft power of an engine can be obtained by employing a ‘torsion meter’ which is used to measure the turning force (twisting force) acting on the shaft. The obtained value is then used to calculate the shaft power being achieved.
‘Propeller power’ is defined as the actual power devel- oped by the propeller due to the revolutions and the pitch angle of the propeller blades.
NB. Propeller power will always be less than the ‘shaft power’ because of friction from bearings and stern tube construction and ‘blade slip’ in the water.
148 The Command Companion of Seamanship Techniques Main engine Flywheel coupling Thrust block Bulkhead gland Stern
gland Stern tube
Tail shaft Propeller Plummer block Intermediate shaft Thrust shaft Thrust key Indicated power Brake
power Developed shaft power
Figure 7.1 Main engine to propeller drive
Figure 7.1 shows diagrammatically the components needed to produce motion at the propeller from the main engine, and Figure 7.2(a) and (b) show typical engine control room console displays.
Engine room records
In the event that a Master is called upon to give evidence to an inquiry or court hearing all sources of information may be required for inspection. These sources may include contemporaneous records such as rough log books and movement books. In the case of the engine room such records may be in the form of:
Data logger information sheets. Engine room telegraph printouts. Bunker records.
Engine Room Log Book. Movement book.
NB. Vessels with less than 150 kW registered power or vessels with unidirectional main propulsion driving controllable pitch propellers whilst on bridge control, and vessels with engines operated by remote control units active from the bridge, are not required to maintain a movement book.
Where vessels are under bridge control, records for engine movements should be contained alongside course
(a)
(b)
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records, echo sounder graphs, telegraph printouts, NAV- TEX reports, etc.
Plant monitoring: unmanned machinery space
With so many different designs of bridge control now in operation it would be unrealistic to lean towards a single system, especially as most operations incorporate all the basic elements needed to provide dual position control. The fundamental system will include bridge instrumentation which monitors and controls:
(a) Propeller speed.
(b) Propeller direction of rotation and/or pitch angle of CPP blades.
(c) Audible and visual alarms on the bridge and in the engineering environment to signal power failure, or other essential control element. (These alarms may be relayed via engineer’s accommodation.) (d) In the case of a diesel engine, ‘air start pressure’
sufficient for manoeuvring.
(e) An independent means of stopping propulsion sys- tems in the event of an emergency.
The alarm system
A total alarm system alerts both engineers and the bridge (when the navigator is the sole watchkeeper) when: (a) a machinery fault occurs,
(b) the machinery fault is being attended to, (c) the machinery fault has been rectified.
The monitoring of systems such as power failure and similar elements will have audible and visual alarm coverage, with means of silencing the audible alarm, but allowing the visual alarm to remain until the fault is cleared. In the event that a second fault develops while the first is being dealt with, the audible alarm is reactivated.
An alarm indicator at a remote station from the machinery space, i.e. bridge, will not automat- ically silence the same alarm inside the machinery space – each and every alarm display once activated will identify the particular fault at either the main control sta- tion or at a secondary station. This effectively increases the more positive response in a shorter time period.
Specific alarm coverage
Where high risk areas such as those subject to fire or flooding are monitored, it would be a requirement
to have two independent monitoring systems interfaced with communications, e.g. bilge level alarm system with direct communication to the duty engineer’s cabin, or a fire alarm from the machinery space direct to the bridge watchkeeping station.
Fire/heat detection systems
Figure 7.3 clearly shows a flame sensor/detector device, in this case fitted to a vessel’s engine room.
Figure 7.3 Flame sensor/detector fitted to ship’s engine room. (Manufactured by AFA Minerva Ltd, Marine and Offshore Division)
Mode of control
It is generally recognized that for a vessel fitted to UMS standards, the normal mode of control will be from the bridge. To effect a change of control from the bridge to the engine room (see Figure 7.4) or vice versa is normally achieved from the machinery space itself. Control station status is of course only initiated with direct communication and on the understanding that the respective station is ready to accept that control.
In the event of system breakdown, the engine room has the capability to revert to full manual control with human intervention. If such an event did occur Masters should be aware that the parameters that were previously automatically recorded and monitored (usually by a data logger) would need to be observed by engineering
150 The Command Companion of Seamanship Techniques
Engine control room
Selector
switch Brige controlnav. bridge
Starting sequence Safety interlocks* * Safety interlocks Acceleration programme Governor Fuel control Starting air Camshaft position
MAIN DIESEL ENGINE
1. No start of main engine with turning gear in position. 2. No start of main engine unless the propeller pitch is
set at zero (CPP).
3. No starting air is admitted once the engine is running. 4. No fuel is admitted unless correct starting sequence
is followed.
5. No astern movement permitted unless engine is first stopped.
6. Main engine cut out if the governor limits are exceeded.
Figure 7.4 Main engine–bridge control: direct reversing diesel engine
staff. This could reflect on response time affecting ship movement as any required change by actuators to attain the desired value would require manual operation as opposed to automatic operation.
Control station change
When changing from one control station to another it is expected that the change takes place simply and effectively. Normal practice dictates that engine room and bridge are both on ‘standby’ and a selector switch is turned to establish the mode of control (see Figures 7.5 and 7.6 for typical engine room features). Once on- line control is accepted the alarm system should be tested and essential control elements checked out as operational.
NB. A basic requirement of operation is that essential machinery could still be controlled manually in the event of bridge control or auto control malfunction.
Emergency fuel shut-off
Most Deck Officers are aware that the ship’s main plant will have remote emergency shut-off controls in such
Figure 7.5 Standby emergency diesel generator turbo-charged air cooler at left hand top end (six cylinder turbo charged engine)
Figure 7.6 Top view of six cylinder, medium speed diesel engine
a position as to be readily accessible in the event of an emergency. The actual positions of these controls will vary from ship to ship but would not be out of place in the Chief Engineer’s office, on an exposed
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boat deck or in a damage/emergency control room. In virtually every case they are a ‘gate valve’ operated mechanically or more usually by electronic solenoid switches, as illustrated in Figure 7.7, to cut fuel supply and so bring machinery to a stop.
Solenoid Closed position Spring Reset lever Open position Emergency push Valve Fuel Oil
Figure 7.7 Mechanically operated ‘gate valve’ used to cut fuel supply
Steam turbines
Data logger links and alarm safeguards for steam turbine plant
ž Lubricating oil pressure for turbines and gearing low.
ž Lubricating oil temperature for turbines and gearing high.
ž Bearing temperature for turbines and gearing high. ž Astern turbine temperature too high.
ž Steam pressure at the gland too high or too low. ž Excessive turbine vibration, generates alarm. ž Axial movement of turbine rotor, if excessive, gener-
ates alarm.
ž Sea water pressure or flow, if reduced, generates alarm.
ž A low condenser vacuum, activates the alarm. ž Condensate level too high, generates the alarm.
Double reduction gearing Double reduction gearing RPM feedback (relayed to bridge and control room) Ahead turbine Astern turbine Actuator Actuator Pressure controller Governor speed controller Speed/pressure transducer Programme timer Programme selector Pressure controller Ahead Stop Astern
Safety interlocks and automatic combustion control Idling cycle Engine control Station isolator selector control Bridge control
Figure 7.8 Steam turbine control system
Figure 7.9 Turbine rotor, exposed and viewed with turbine casing removed
Automatic ‘stop’ occurs if the lubricating oil is lost completely. Speed reduction occurs if the machinery experienced excessive vibration or axial distortion or if condenser problems existed.
152 The Command Companion of Seamanship Techniques
Turbine operations incorporate automatic back-up systems if:
(a) there is any loss of pressure of lubricating oil, (b) the condensate pump slows,
(c) the main sea water circulating pump slows.
The closed feed system
The principle of the closed feed water system (see Figure 7.10) is to generate steam from the water in the boiler to carry the heat energy to drive the plant. The ideal system would be to recover the steam at the end of its cycle and return it as feed water, without incurring any loss. Superheater HP LP Eduction pipe Regenerative condenser Main feed check valve Boiler Economizer Steam drain Surface feed heater Main feed pump Deaerator Surge tank Pump Reserve feed tank
Figure 7.10 Closed boiler feed water system for use with turbines
In the closed feed system there is a need to mini- mize the loss of water and heat – essential savings at any time, but never more so than with a shipboard system. Some heat can be utilized to increase the overall effi- ciency of the plant, and to vent steam off to atmosphere would create a need for considerably greater quantities of ‘feed water’ to be available.
The essential aspects of the feed system are: (a) To transfer the condensed steam (condensate) from
the condenser back to the boiler via the deaerator and feed heater.
(b) To increase the efficiency of the plant by use of feed heaters which employ live steam direct from the turbine or exhaust steam from auxiliaries to increase the feed water temperature.
(c) To provide quality controlled feed water by mon- itored analysis in order to protect the boiler from impurities and the effects of scale.
Figure 7.11 Water tube boiler, viewed from inside the furnace area
The water tube boiler, as seen from inside the furnace area, is shown in Figure 7.11.
Engine room operations and maintenance Cascade system
The cascade system employs a Master controller, which emits an error signal (E), to activate another slave control section. A similar system monitors the level and supply of water delivery to the boiler when steam demand is high.
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Figure 7.12 Piston removal from a slow speed two-stroke crosshead engine
Figure 7.13 Condenser opened for maintenance
Figure 7.14 shows boiler fuel and air delivery being generated from the pressure and flow sensors monitoring the main steam line. When demand by consumables is high an initial error signal activates the master steam controller which subsequently activates the two slave systems controlling the air and fuel.
* *
Boiler
Furnace
Pressure
sensor sensorFlow Adding relay − − − + + + MV MV DV (Master controller) DV DV MV E E E Steam pressure controller Air flow controller Air flow sensor Actuator From combustion air fan
Combustion air damper To boiler burners Fuel valve From fuel pump Actuator Fuel oil sensor Fuel oil
controller Fuel limitingrelay Fuel limiting relay receives
a feedback signal from the air flow sensor and compares required fuel rate with air availability. Fuel rate cannot be increased until an increased air flow signal allows alteration to the desired value setting at the fuel controller.
Steam line
Figure 7.14 Cascade control system: boiler steam
NB. The measured value (MV) is compared with the desired value (DV). If these two values are not similar then an error signal (E) would be generated to activate the controlled element.
Boiler terms
Priming
A fault in the boiler due to overheating, where water is actually carried over with the steam. A highly undesir- able condition which could lead to erosion and the cause of ‘water hammer’.
Shrinkage
An apparent loss of the water level in the boiler due to a reduction in steam demand, e.g. if a vessel is steaming at full speed and drawing full steam supply, and is then suddenly reduced to half speed, a back pressure is momentarily experienced. This is detected by the water level sensor gauge which actuates a top-up by the feed water control.
Swell
The opposite effect to shrinkage where an apparent increase in the water level is caused by increased steam demand.
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Engineering duties Prior to arrival standby
When arriving at a port it is the duty officer’s responsi- bility to keep the engineering department fully informed of the vessel’s progress to ensure that when the engines are required the essential tasks for manoeuvring have been completed. Such duties vary depending on the type of engine but the following example is provided for a ‘slow speed diesel’.
Normal practice includes checking the air start sys- tem, i.e. all bottles are full and ready for operation and all valves are lubricated. Prior to standby, the heavy fuel system is changed to diesel oil and the revolutions are reduced slowly to avoid damage to the pistons.
The manoeuvring handles are oiled and additional personnel placed on standby duty. Once the vessel is placed on standby, the auxiliary scavenge air pump is started and the air start system valves opened up to make the system ready for immediate use.
At full away
Once a vessel has cleared the standby area the Master is expected to order ‘full away’ and the engine room personnel should be actively engaged in bringing the vessel up to full sea speed.
Initially the auxiliary scavenge air pump is shut down, and the engine’s speed gradually increased from full manoeuvring. The change from light diesel fuel to heavy fuel oil for normal running is carried out slowly before the vessel attains ‘full sea speed’. Sea watches are set and additional standby personnel stood down.
At finished with engines
When a position is reached that ‘finish with engines’ (FWE) is ordered the main machinery will gradually be shut down. Initial actions entail opening the drain valves to release the fuel pressures and closing the outlet valves to the high pressure fuel filters, and closing down all fuel pump suction valves leading from gravity tanks to prevent the risk of leakage through the pump and filter drains.
NB. The head of a gravity tank could be sufficient to lift suction valves of a fuel pump.
The circulation of cylinder jackets and pistons is con- tinued for about half an hour after stopping, to allow uniform cooling to take place. The sea water cooler and the oil lubrication systems are then stopped and shut down.
Control and monitoring of machinery and plant systems
The modern vessel is fitted with many operational sys- tems to allow the ship to be worked as a floating trans- port. Cargo, ballast and fuel systems are common to all types of commercial vessel and they are all often fit- ted with a variety of actuators, sensors and controllers in order to function (see Figure 7.15). When the instru- mentation to a plant or specific system is extensive, the task of monitoring and assimilating information becomes a major task which can be labour intensive and time consuming.
Figure 7.15 Cargo control room console display
With smaller crews and larger vessels being the order of the day the need for effective control sys- tems becomes essential, and was positively addressed by the introduction of ‘data loggers’ and ‘mimic dia- grams’. These relieved labour problems and central- ized shipboard monitoring operations to specific control rooms.
Mimic diagrams
A mimic diagram is a pictorial representation of the