The Officer of the Watch should be familiar with the operation and limitations of the engine /propeller control mechanism.
The following information will be helpful to a deck officer to understand the operation and limitations of machinery under different situations. It is advisable that the Officer of the Watch give timely notice of engine movements, when possible. However, he should bear in mind that the engines are always at his disposal and he should not delay/ hesitate to use them in case of need.
Minimum numbers of starts needed as per regulations for a reversible Main Engine (ME) with fixed pitch propeller:
Regulation states that a minimum of 12 consecutive starts are required alternately in ahead and astern directions for a reversible Main Engine coupled to a fixed pitch propeller. The total reserve of compressed air quantity onboard, without replenishment, should be able to achieve this. For example, if there are two air bottles the total amount of reserve air in both the air bottles should be sufficient to start the engine 12 times alternately in ahead and astern directions. For a non-reversible engine coupled to a CPP the required number of starts is 6.
Number of times, the Main Engine on my vessel can be started with the reserve air in the air bottles:
Refer to Sea trial records. Though there are theoretical ways to find this out, the best way would be to do the actual trial of starting the engine in ahead and astern directions (say at the anchorage) till the time the air pressure in the air bottle has dropped to a level where the engine cannot be started any more. You can count the kicks from the first kick to the last kick. Ensure your air compressors are in good order before doing the test. Vessel’s condition will not be the same as it was during the sea trial and hence the number of starts demonstrated during sea trial may not be achieved during the service life of the vessel. Therefore it is advisable to have a realistic figure by conducting tests during anchorage.
Why the engine rpm should be brought up or down gradually from the Manoeuvering ‘Full Ahead’ rpm?
Abrupt or fast changes in the engine load may cause large difference in temperature on the inner and outer walls of piston and liner, which will finally result in high thermal stress. This may lead to premature failure of cylinder liner or piston. Hence the change in rpm should be gradual.
Can the ‘load up’ or ‘load down’ programme be bypassed while increasing or decreasing the engine rpm by pressing the load programme cancel button?
Load up or down programme permits gradual increase or decrease of engine rpm beyond a certain engine rpm decided by the engine manufacturer. It is built in the engine control to ensure that the thermal stresses in the engine parts are maintained within tolerable limits. If we bypass the load programme, the engine rpm can be brought up or down much faster but the risk is that the engine parts have to withstand much more stress. However master may decide to cancel or bypass the load programme for justifiable reasons to save the vessel from imminent dangers such as grounding/ collision etc.
Situation under which, Main Engine ‘auto slow down over-ride’ button on the bridge console can be pressed:
Auto slow-down of Main Engine is activated in case some of the important engine parameter could not be maintained within safe limits. This is to protect the engine from damage.
However, for justifiable reasons to save the vessel or to save a disaster from happening,Master can override the auto slow down and put the Main Engine to some risk.
Situations under which the ‘Emergency stop ’ from the bridge console should be activated:
This button must be pressed only if the normal way of stopping the engine i.e. by using telegraph or engine control lever, is not responding. However, do not have the impression that the button must be pressed just because there is an emergency like imminent grounding, allision or collision etc. If the engine cannot be stopped by normal means and is required to be stopped, then the emergency stop button can be pressed.
Manual emergency shutdown can be operated from any of the positions (Bridge, ECR or Local control) regardless of the control position for operating the main engine.
To ensure watchkeeper’s familiarity with operation and limitation of bridge manouvering, drills should be conducted as per drill planner under Chief Engineer’s supervision.
Astern manoeuvre steps (Normal):
When the engine is operating in ahead direction and now you want astern movement, the following will be the sequence of events:
a. Bridge orders astern rpm.
b. Engine room acknowledges astern command on telegraph (when in Engine Control mode). In case of Bridge control this happens automatically from the engine.
c. Main Engine fuel supply is immediately put to zero.
d. Engine may continue to turn in ahead direction due to the momentum of the vessel even if the fuel supply is cut off, hence the tachometer on the bridge may still show ahead rpm.
e. Engine (Engineer will do this it is in Engine control mode) is now waiting for the rpm of the engine to come down to zero
f. As the engine stops turning, astern starting air is admitted.
g. As the engine rpm reaches the start level, fuel is injected.
h. Engine starts turning on fuel in astern direction.
In case the Master needs the astern power urgently to avoid a mishap, it must be communicated to engine room clearly. This is a ‘Crash Astern’ situation and the action of engineers will be as in below point 8, i.e., different from the above steps for ‘normal astern’.
Crash astern steps
When the engine is operating in ahead direction and a crash astern movement is given, the following will be the sequence of events:
a. Bridge orders crash astern. The communication to engine room:
i. When in Engine room control mode – Conventionally bringing the bridge telegraph from ahead to full astern then again to full ahead and again to full astern was the standard way to communicate crash astern to engine room. Engine room implements the astern command given by bridge on telegraph.
ii. When in Bridge control mode – In modern ships with automation and controls, the bridge telegraph is directly connected with the engine controls and it doesn’t require involvement of engine room personnel. Such type of telegraph is called remote controlled telegraph device.
A provision is given to link both the telegraph so that manual operations can also be carried out in case of automation failure.
In bridge control mode, to give crash astern, Bridge officer should directly put the telegraph to Emergency Full Astern or full astern, as available. Engine will automatically comply with the order.
b. Main Engine fuel supply is immediately put to zero
c. Engine may continue to turn in ahead direction due to the momentum of the vessel even if the fuel supply is cut off, hence the tachometer on the bridge may still show ahead rpm.
d. Engine (Engineer will do this it is in Engine control mode) is now waiting for the ahead rpm of the engine to come down to the reversing level as prescribed by the engine manufacturer (which is around 25% to 30 % of MCR rpm)
e. As the engine rpm reaches the reversing level, admit starting air (in the astern direction) this is also known as braking air. Attempting to admit the braking air at higher rpm is termed as “braking air”, which can cause very high level of Stresses and break the crank shaft.
f. Repeated kicks of braking air are then given to bring down the engine rpm to zero.
g. Once engine rpm is at zero, starting air in astern direction is admitted
h. As the engine rpm reaches the start level in astern direction, fuel is injected.
i. Engine starts turning on fuel in astern direction
j. Vibration may be set up due to heavy wake disturbance; hence the astern rpm will have to be gradually increased. Similar sequence will automatically take place on a ‘bridge controlled vessel’.
Crash astern will not immediately stop the vessel which was moving in ahead direction with full speed, it will take some time. The Bridge team should be familiar with the following data on their vessel:
i. How much time will it take for the vessel to stop after the crash astern order is given?
ii. How much distance will the vessel travel before it stops?
The complete shafting including engine crank shaft, intermediate shaft, tail-end shaft and propeller has a certain natural frequency of vibration in the torsional mode (i.e. twisting and untwisting mode). If engine’s firing frequency during operation is same as this natural frequency of shafting system the amplitude of vibration in the torsional mode will go very high. As a result of that, high degree of torsional stresses may be set up which may cause the failure of engine crankshaft or some other part of the shafting system. Critical range of rpm is the main engine rpm range in which the engine should not be operated continuously to avoid high amplitude of torsional vibration. All engines necessarily do not have a critical range of rpm. If your engine has a critical range of rpm, the rpm indicator will have that range marked in red colour, also the critical range of rpm will be written at the maneuvering console. It is advisable to ask your chief engineer once to check whether the figures written or the marking done on the Main Engine rpm indicator on the bridge is correct.
While manoeuvering from bridge, importance of ensuring that the engine rpm does not stay in the critical range while taking the rpm up or down:
Some of the engine control systems are fitted with critical speed jumping device which ensures that the rpm does not stay in the critical range for long. However, on some of the ships it will depend a lot on the skills of the operator to ensure that the engine never operates continuously within the critical rpm range. For example, while bringing down the rpm from full away suppose the control is kept to a rpm just below the critical rpm range the engine may stay in the critical range dangerously for a long time as the vessels momentum will not allow a quick reduction in the engine’s speed. To avoid this situation, it is wise to keep the engine control at much below the lower range of critical rpm, so that the engine crosses over the critical range quickly.
Check Communication Systems:
Communication forms the basic and primary ingredient for starting and further operating main engine smoothly from any designated location, before using main engine the communication between the Bridge, the Engine Control Room and the local manoeuvring platform is to be checked. The fixed communication system, hand powered telephones, talk back system, walkie talkies to be used should be checked and ensured in good working order at all times.
Checking Propeller clearance:
Before trying out or operating main engine it must be ensured that the propeller is clear of any nets, fishing lines, ropes, trawls or any other unwanted objects. Often while vessel is stopped, lying at anchor, berthed alongside a pier, jetty or berth or moored at single point mooring there are tug ropes in water or fishing nets or broken lines floating, which might get entangled in the propeller fins and damage it. Hence it’s important that such things are cleared before rotating the propeller.
Make Sure Engines Are Tried from ECR before taking Over:
It is very important to ensure that the propulsion plant is in good condition so that no trouble is faced when the engine is running during manoeuvring. This can be better done by engineers who can assess the clear picture if the engine is tried for ahead and astern from ECR before transferring the controls to the bridge.
Informing the engine room before major course alterations:
Rudder when put to higher angles puts additional load on the engine. If the engineers are aware about the course alteration, they can monitor engine parameters more closely and take corrective actions if needed.
Torque rich condition:
In simple terms, the maximum power the engine can produce has a limitation w.r.t. the engine rpm as established by the engine maker. Any attempt to produce higher power will result in damage to the engine. So at any given point of time, if the engine is producing higher power than it is permitted to produce at that rpm, it is said to be operating in ‘torque rich condition’. If the engine NCR Rating is 10,000 BHP, it does not mean that the engine can produce 10,000 BHP at any rpm. For example the engine can be operating in the torque rich condition even at slow ahead if the resistance to the vessel movement is too high, say the vessel has run aground. Electronic governors are capable of sensing this condition and they limit the fuel supply to engine which will consequently result in engine operating at lower than desired rpm. A light showing ‘torque rich condition’ or ‘fuel limit’ will also glow on the panel. In other vessels fitted with conventional hydraulic governor, the ship’s staff has to take care to avoid torque rich condition of the Main Engine.
Boiler soot blowing:
A soot deposit continuously takes place on boiler tubes during its operation. Best way to remove this soot is to periodically do it by physically accessing and cleaning the heat transfer surface. However, during the service of the boiler, the soot is removed using steam or compressed air mixed with chemical. Steam used for soot blowing can not be recovered and hence that much water is lost every time we soot blow. Soot blow may result in the soot coming out from the funnel and falling on the poop deck and accommodation area.
sometimes it may be necessary to soot blow the exhaust boiler due to soot accumulation caused by long manoeuvering just prior arrival port, making the poop deck dirty, which was cleaned just a few hours ago. Good coordination between deck and engine departments will cleaned just a few hours ago. Good coordination between deck and engine departments will prevent occurrence of such problems.
Bow Thruster operation:
The deck officers operating the bow thruster joy-stick must never increase the pitch from minimum to maximum in one go. It can lead to sudden increase in current and damage or trip the motor as the Bow Thruster (BT) system involves using high voltage and current.
Also, maximum given pitch should never exceed 90% and operation at higher pitch must not be continued for long duration of time.