Emergency preparedness for management of main propulsion engine failure on a bulker during harsh weather at sea
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Bulkers are vessels that carry various types of cargo, which includes coal, iron ore or grain ranging from 3000 deadweight tonne (dwt) to 400,000 dwt. These bulkers are propelled by large marine diesel engines the capacity of which ranges from 4000 kW to 80,000 kW. The owners of the bulkers generally charter the vessels to reputed charter parties for mutually agreed terms and condition, the main specifications being the vessel speed in knots and the fuel consumption in tonnes per day respectively. Safe transportation of the bulk cargo from one port to another at the specs of the charter party is a great challenge for the vessel’s chief engineer. Moreover, there is a likelihood of the vessel coming to a halt in a harsh weather condition, because of the main engine failure. Thus, the seafarer’s on-board ship needs to be well prepared to handle such an emergency in a harsh working environment. This study looks at the likelihood of main engine failure during harsh weather at sea and effective ways of managing the emergency. The findings of this study will work as a guide for the seafarers and helps to manage the risk on-board ship.
KeywordsMain engine Failure Bulker Harsh weather Risk management
In the commercial shipping industry, bulk carriers are specialized vessels which safely transport bulk cargoes ranging from 3000 dwt to 400,000 dwt safely from one port to another. These vessels are chartered by reputed charter parties who hire the bulk carriers for a certain period (Hatzigrigoris et al. 2006; Nunes 2003). These vessels are propelled by highly powered marine diesel propulsion engines ranging between 4000 kilowatt (kW) to 100,000 kW (Cepowski 2017; Pundars 2018). A bulk carrier propelled by a large slow speed two stroke diesel engine, directly coupled to a propeller is being considered in this study. These vessels are hired by reputed charterers for a fee depending upon the tonnage of the cargo transported (Houvardas 2017). The charterers generally referred to as a charter party in merchant shipping pay the ship manager / owner for fuel and the vessel is expected to perform an agreed speed. The charter party clause specifies fuel to be consumed in terms of metric tonnes per day and the ship speed in knots. An allowance of ± 5% is permitted for the fuel consumption and speed also forms part of the charter party clause. The chief engineers and the masters are required to send the fuel consumption and the engine speed records daily to the charterer. It is a big challenge to the vessel’s chief engineer to attain the requisite speed, which needs to be closely monitored (Houvardas 2017). The variation in the ship speed will also depend on the wind condition and weather. Attaining the charter party speed during calm sea is not an issue. However, it is a very big issue while the vessel undergoes harsh condition and faced with rough weather. During the adverse weather condition, the vessel will be unable to acquire the specified charter party’s speed due to a great variation on a load of the main propulsion engine, because of the vessel’s rolling and pitching effect which leads to the ship’s propeller continuously submerging and emerging out of the water. There are many accidents happened on-board ship due to the rough weather (Islam et al. 2017; Islam et al. 2016a; Islam et al. 2018a; Islam et al. 2018b; Islam and Yu 2018). The above phenomenon is expected during rough weather and special precautions require to be taken when the vessel encounters harsh weather. Therefore, the chief engineer of the vessel should be well prepared to manage the main engine operation during adverse weather condition (Kazimierz, 2017).
There are numerous studies conducted by the researchers for the failure detection of main propulsion engines (Balin et al. 2016a; Balin et al. 2016b; Balin et al. 2018; Demirel et al. 2015). Researchers (Balin et al. 2016b) used the Fuzzy Analytic Hierarchy Process (AHP) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methods applied in failure detection of a gas turbine. Researchers (Balin et al. 2016a) applied fuzzy AHP combined with the fuzzy VIKOR technique to evaluate risk assessment of the gas turbine. Researchers (Demirel et al. 2015) puts forward a fuzzy Multi-Criteria Decision Making (MCDM) methodology to determine the breakdown of main diesel engine equipment. Finally, researchers (Balin et al. 2018) applied the fuzzy Decision-Making Trial and Evaluation Laboratory (DEMATEL) approach to examine the causes and the weights of the faults and their relation to each other in the auxiliary systems of the main engine. However, the above study doesn't particularly focus on marine engine failure in the harsh weather at sea nor addressed the risk management procedures. Therefore, to fill this knowledge gap this study focusses on the management of the ship’s main engine during the harsh weather at sea. This study will help seafarers on-board ship to look at the risk management procedure for each subsystem of the main engine to reduce the hazards. This paper is organised as follows: Section 2 presents the fault tree representation of the stoppage of bulker at sea. Moreover, section 3 and 4 represents individual risk management and collective risk management of the main engine respectively. Finally, conclusions are presented in Section 5.
Fault tree representation of the stoppage of bulker at sea
To begin with a fault tree representation for the abrupt stoppage of the bulker at sea is considered (Song et al. 2012). The basic events leading to the top undesirable condition which includes failure of the main engine, power generation plant and vessel’s steering system. The basic events leading to the failure of the main engine is then considered Fig. 1.
Steering gear failure
The steering gear comprises two hydraulic pumps driven by the electric motor which drives 4 hydraulic rams. The rams are connected to a tiller arm which in turn drives a rudder stock to which the rudder is connected. The rudder steers the vessel between 35 degrees port to 35 degrees starboard. The steering position is dictated by a transmitter on the ship’s bridge and received by a receiver in the steering gear platform by means of hydraulic controls. The rudder is steered to the required helm angle. In case of a bridge control failure, there is a provision to steer the vessel from the local steering gear platform. Failure of steering gear at sea could lead to a disastrous consequence especially in a harsh weather environment (ATSB 2012).
Power plant failure
The power generation on a bulker is normally provided by diesel generation sets. There are generally three auxiliary diesel engines which drive a generator and supply power to the main switchboard. Three auxiliary engines are normally installed as per the requirement of Safety of Life at Sea (SOLAS) convention one auxiliary engine should be able to supply the full load for the bulker during sailing and the other two will be on standby duties (Balin et al. 2018). Failure of the auxiliary engines could end up in a blackout at sea or whilst at anchorage. It may also result in the grounding of the bulker (ATSB 2018).
Main engine failure
- i = 1
is the lube oil system,
- i = 2
is the fuel oil system,
- i = 3
is the cooling water system
- i = 4
is the scavenge air system
It can be seen from the RBD that the 4 sub-systems of the main engine are in series. Failure of any one of the sub-systems will result in failure of the main engine (Anantharaman et al. 2018a). It will ultimately result in stoppage of the bulker at sea which would be catastrophic (Martinović et al. 2011). Therefore, the chief engineer needs to ensure to avoid such a situation during rough seas in a harsh environment. Necessary steps require to be taken to manage this situation (Malik and Briddon 2011). Hence, it is required to look at each of the sub-systems, and the hazards involved to mitigate the risk.
Individual risk Management of Main Engine
During the harsh weather condition, the vessel will have a great variation on a load of the main propulsion engine because of the vessel’s rolling and pitching effect which leads to the ship’s propeller continuously submerging and emerging out of the water. As a result, the main engine’s performance will affect significantly and increases the hazard in various subsystems. To determine the risk management of the main engine, it is essential to investigate individual risk management of the subsystems (i.e. Lube oil system, Fuel oil system, Cooling water system and the Scavenge air system). Individual risk management of each of the sub-systems addressed in section 3.1 to 3.4.
Lube oil system
The main engine lube oil system consists of a lube oil of pumps that draw oil from a large capacity lube oil sump and sends the oil through discharge filters (Islam et al. 2019). The oil is then filtered and cooled in a seawater cooler. A temperature control valve maintains the correct temperature, and the oil is sent to the main engine for lubrication of bearings and cooling the piston (Sadatomi and Ito 2016). Normally, one pump would be running and the second one is kept as a standby for the emergency purpose Fig. 3.
In harsh weather at sea, ships will roll and pitch as a result the lube oil pump loses the suction which will affect the lubricating system of the main engine. Moreover, during this condition, it is very difficult to keep the correct sump level of all the machinery resulting in false level alarm which can trip the running machine and lead to a dangerous situation. Furthermore, the lube oil filter can get clogged and stand by pumps can go on/off due to the great fluctuation of pressure as heavy sea waves will put extra load on the main engine.
The hazards and threats from the main engine lube oil system and the corresponding risk management are shown in Fig. 4.
Fuel oil system
On the other hand, bad weather involves the resonant movement of engine oil in the crankcase, and the engine oil pump is momentarily exposed to air which will affect the engine fuel oil system. Moreover, during bad weather ships will roll and the fuel oil pump loses the suction which will affect the fuel supply system of the main engine. During this condition, it is very difficult to keep the correct sump level of all the machinery resulting in false level alarm which can even trip the running machine and lead to a dangerous situation. Moreover, low fuel supply “direct cause” of the engine failure. Besides, in bad weather stern swell often causes the propeller to emerge out of water for a fraction of seconds during the time period of swell. Thus, a reduction in resistance near the propeller results in racing of the propeller and a surge in the load on the main engine. Due to this load variations, the fuel rack of the engine fluctuates and causes engine failure. The above hazard leads to the engine failure and increase the chances of fire and explosions on-board ship.
The main engine fuel oil system consists of a fuel oil settling tank where the fuel is transferred from the vessel’s storage tanks (Islam et al. 2016b). The fuel oil from the settling tank is supplied to fuel oil purifiers and the purified oil is sent to the service tank. Both the fuel oil settling, and service tanks have a quick closing outlet valve. This valve can be closed from a remote position (outside the engine room during an emergency) (Anantharaman et al. 2018b). The purified oil from the service tank is supplied to fuel oil supply pumps, where the fuel pressure is raised to about 4 bars and then supplied to booster pumps where the pressure is further increased to 10 bars. The booster pump sends the oil to a fuel oil heater where the oil is heated to 135ºC (depending on the viscosity of the oil), before entering to the main engine fuel pumps and injector. The viscosity at the inlet to the main engine fuel pump should be 10-15CST. The main engine fuel pump raises the pressure of the fuel oil from 10 bars to 1000 bars and supplies to the fuel injector where the fuel is atomized. Also based on the load of the engine the volume of the fuel supplied to the engine would vary and it can be controlled by the fuel rack on the fuel pump Fig. 5.
During rough weather, there will be a great fluctuation in the movement of the fuel rack, varying from maximum to a minimum value, which could also result in the stoppage of the main engine. The hazards and threats from the main engine fuel oil system and the corresponding risk management is shown in Fig. 6.
Cooling water system
Generally, main engines on-board ships are cooled by seawater. The water pumps are used to pump seawater into the engine cooling system. However, in bad weather conditions, waves in stormy seas cause a vessel to pitch and roll in a manner to cause air instead of seawater to enter into the engine cooling system. As a result, it affects marine engine cooling and causes overheating to the engine parts. Moreover, the film of the lubricating oil will get oxidized due to the lack of cooling and helps to produce carbon deposits on the surface. This will result in a piston seizure. Furthermore, the lack of engine cooling may lead to a distortion of the engine components due to the thermal stresses set up and decrease the volumetric efficiency of the engine. The cooling water system consists of an expansion tank, cooling water pumps, and a temperature control valve. The potential hazards or threats from the cooling water system during harsh weather could include fluctuation in water level in the fresh water expansion tank. Moreover, the variation of cooling water pump pressure could result in coming on / off the cooling water pumps Fig. 7.
The hazards and threats from the main engine cooling water system and the corresponding risk management are shown in Fig. 8.
Scavenge air system
The main components of a scavenge air system includes a turbocharger, which draws air from the engine room at a pressure slightly above the atmospheric pressure and the air is compressed to a pressure of 4 bars at a temperature of 120ºC. This air is then cooled in an air cooler to a temperature around 40ºC. It is then sent to the scavenge space of the engine from where it flows into the engine cylinders via scavenging ports in the cylinder liner. An auxiliary blower is available to supply air to the engine at low loads Fig. 9.
The hazard or threats from the scavenge system would include surging of turbochargers during the load fluctuation of the engine. This could lead to disastrous consequences, leading to breakage of the turbocharger in extreme case. The hazards and threats from the main engine scavenge air system and the corresponding risk management is shown in Fig. 10.
Collective risk management of the main engine
is bad weather matrix
Vessel rolling and pitching heavily
is Hazard / Threat matrix h1
pump losing suction
filters getting clogged
standby pumps coming on / off due to great fluctuation in pressure
is Risk management matrix
keep the lube oil sump level 15% higher than normally recommended
all filters to be cleaned before the start of the voyage
keep the pumps on manual. consider moving away from UMS to normal watchkeeping duties for engineers.
Vessel Rolling and pitching heavily
is Hazard / Threat matrix
accidental closure of tank quick closing valve
pump losing suction
filters getting clogged
standby pumps coming on/off due to great fluctuation in pressure
fluctuations of fuel rack due to load variation on the main engine RMF is a risk management matrix
keep a close eye on the tank quick closing valves
regularly drain settling and service tanks for water and sludge
all filters to be cleaned before start of the voyage. keep a close eye on the pressure drop across the filter
consider moving away from UMS to normal watchkeeping duties for engineers
main engine on manual control. reduce load mon the engine to keep the load fluctuations to a minimum
vessel rolling and pitching heavily.
is Hazard / Threat matrix
expansion tank level fluctuation.
standby pumps coming on/off due to great fluctuation in pressure.
is a risk management matrix.
closely monitor expansion tank level
keep the pumps on manual and consider moving away from UMS to normal watchkeeping duties for engineers.
is bad weather matrix
vessel rolling and pitching heavily
is Hazard / Threat matrix
surging of turbochargers
fluctuation in the engine load.
is risk management matrix
keep a close eye on the turbocharger operations.
consider moving away from UMS to normal watchkeeping duties for engineers
load on the engine to be reduced to keep load fluctuation to a minimum
After careful observation of the above matrix, it can be concluded
BWME (Bad weather main engine) = [b1] =[b2] =[b3] =[b4] = [b] (As, BWL, BWF, BWC and BWS are identical)
It is to be noted that, lube oil system, fuel oil system and the cooling water system have a pump normally running and the second pump in the standby mode. During bad weather, the performance of all the system’s pump needs to be monitored simultaneously, hence it is reasonable to conclude that h1 = h5.
Moreover, the filters for the lube oil system and the fuel oil system need to be closely and simultaneously monitored during bad weather hence, it is reasonable to assume that h2 = h6.
On the same ground it is reasonable to assume that h3 = h7 = h10, h8 = h12.
The risk management matrix RML, RMF, RMC and RMS are the lube oil, fuel oil, cooling water and scavenge air system respectively. Close identification of the matrix elements leads to a conclusion that r2 = r6, r3 = r7 = r10 = r12, r8 = r13
From 1, 2 and 3 the emergency preparedness matrix for a bad weather can be represented as.
Equation 4 represents the key elements of the 3 matrices BWME, HZME and RMME and aids the ship engineers to be better prepared to handle the emergency stoppage of the main engine. The collective risk management of the main engine presented in Fig. 11.
This study investigated several main engine subsystems which could lead to failure of the main propulsion engine due to bad weather in a harsh working environment. By using matrix algebra collective risk management strategy for the main engine is developed. This will help the ship’s engineer to identify the cause of main engine failure in a harsh working environment. Moreover, marine engineers on-board ship should look at the risk management procedure for each sub sytem suggested to reduce the hazards.
As a result, the ship’s engineer will be better prepared to handle and avert main engine failure in a harsh environment. This principle could be extended and applied to other systems on-board the bulker, that would aid in averting problems on the respective systems in a harsh working environment.
The authors thank National Centre for Ports and Shipping at the Australian Maritime College of the University of Tasmania for the conference support.
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