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The main propulsion engine's bedplate will usually be bolted to the top of the tank in the engine room. Lubricating oil from the engine drains by gravity back into the sump, through the gratings or other small perforations below the crankcase. The main propulsion engine’s sump is usually of the “dry type," where the lubricating oil is stored underneath the main engine in a tank called the "Sump Tank." A separate lubricating oil pump takes suction from the sump tank and delivers it under pressure to the engine. Refer to the attached diagram for a general layout of the main engine lubricating oil sump. (Click image to enlarge.)
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The vessel had a four stroke main propulsion engine made by Akasaka Diesels, Ltd. of Japan. After discharging at a port, the vessel was about to set sail towards China for loading. The pre-departure checklist was completed and the Pilot boarded the vessel. The Engines were tried out and were on “Stand-by." The vessel started maneuvering and departed the coastal waters.
There was an alarm: “Main engine lube oil sump tank low level." I immediately asked the Oiler to sound the tank for the quantity. Before departure, the sounded quantity was approximately 10 tons and the oiler, after sounding the tank, reported that there was approximately a reduction of 5 tons. I reported the issue to the Second and Chief Engineer immediately and asked the Oiler to sound all tanks near the sump tank. I also called up the bridge and enquired about the visibility of any oil sheen on the sea. The bridge reported back that everything was normal and there were no traces of oil on the sea.
In the meantime, the oiler reported back that all other tank soundings were normal. We assumed that the change in sounding was due to the change in trim and draught of the vessel after discharging the cargo. In order to safely navigate out of the coastal waters, the Chief Engineer ordered topping-up the sump with approximately 3 tons of fresh lube oil. The Oiler sounded the quantity and reported that the final quantity was 8 tons.
As the Pilot disembarked, the vessel was ordered full away by gradually increasing the speed. To our surprise, again the “Main Engine Lube oil sump tank low level" alarm sounded. Now all the Engineers came down to the control room wondering what could be going wrong. The Oiler sounding the tank again reported that there was a reduction of approximately three tons and all other tank soundings were normal. We decided to stop the engine after informing the bridge.
We decided to open up the crankcase for inspecting the oil level through the grating. The Second Engineer ordered me to stop the lubricating oil pump and shut off the starting air. As I proceeded to stop the pumps, the Second Engineer went to open the crankcase.
After stopping the pumps, I went down to the bottom platform and suddenly saw huge quantities of lubricating oil flooding the engine room. The Second Engineer came rushing towards the stair case to climb up to a safer zone. After witnessing the reduction of oil flow, we both descended down to the bottom platform. As I looked into the crankcase, I found it to be flooded with lubricating oil. Now we realized that the oil did not “escape" anywhere, but was instead filling up inside the crankcase.
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How and Why the Problem Happened
We emptied the lubricating oil from the crankcase to the lubricating oil settling tank using a pneumatic portable pump. After emptying out the compartment, when we went inside the crankcase, we found three valves in the closed position. We immediately went to the control room and looked at the manual which explained about this arrangement. We located the valve operating hand wheels with extended spindles located underneath the floor plate. We immediately opened those valves and found everything clear.
The engine had an option of using the crankcase like a wet type sump, in the event of buckling or any damage to the main lube oil sump. If the main lubricating oil sump happens to buckle in case of grounding or other emergencies, the crankcase can be used as a sump to maintain propulsion. This arrangement had three butterfly valves, which separated the crankcase form the main lube oil sump.
The three butterfly valves were provided to isolate the lube oil sump from the engine crankcase. These three valves were inside the crankcase with an extended spindle, such that it can be operated form the engine room bottom floor. But none of us onboard the ship knew about this special arrangement. We all were thinking about the conventional dry sump type arrangement.
Later we found that the automatic closing of the valves was due to vibration. These valves were unknown to the engineers and no maintenance had been carried out over years together. Thus over a long period of time, these valves must have started to close slowly and thus resulted in loss of around ten tons of lubricating oil. We kept the valve open and lashed it to the angle bar. We also painted the floor plate covering the valve hand wheel with red color and made a placard mentioning the valves.
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I Learned from That
It is always better to learn about any engine which you haven’t previously worked on. Every engine has its own special feature and nothing can be assumed to be common for all engines. We Engineers have learnt only the basic operation with which we have to extend our knowledge and sense to match different engine room conditions.