Blog 136 - "Marine Musings" - Smells and a Thrust Block

Smells and a Thrust Block

As much as sounds play an important role in an Engineer’s observation  and inspection of an Engine Room, smells play an equally important, if not a more important role in detecting anomalies with the operation of different machinery.

Old Socrates saying: “He who smells the crispness of dollars, comes into money”.

Old Chief Engineers’ saying: “He who smells something in the Engine Room, smells trouble”

There are so many smells that pervade the Engine Room that to assimilate them and differentiate between them sometimes becomes a problem. One has to train himself (or herself, in today’s shipping world) to patiently - and laboriously - trace a smell to its source and, after identifying the source of the smell and rectifying the fault, file it away in memory for future reference.

This way, various smells can be identified quickly and the Engineer can home-in on to the primary source.

Electrical smells are, relatively, the easier ones that can be identified. An electrical wire insulation burning gives a slightly different smell from a motor burning.

Compressed air that is leaking, apart from the sound, gives a rich smell of oxygen as well as a slight smell of humidity that reminds you of rains at home.

Freon leaks from the ‘Fridge or AC Systems give out a very distinctive smell. One has to be very careful around this smell, as it causes respiratory problems. Freon gas release in close proximity to an open flame, results in formation of phosgene gas, dangerous.

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A Main Engine cylinder that is having a ‘blowpast’ gives a peculiar smell. You then rush to see which exhaust temperature is shooting up and take appropriate action.

And then there are the different smells of the different oils.

Heavy Fuel Oil (heated to 120 to 140 deg C), when leaking, gives off a ‘hydro carbon’ smell that straightaway leads you to the leak.

Here I have to digress a bit to warn Engineers of the dangers of a ruptured High Pressure Fuel Pipe, the pipe from the Fuel Pump to the Fuel Injector. The rupture of this pipe can be smelt from all over the Engine Room. The escaping fuel - leaking from either a ruptured pipe or a connecting joint - will be in the form  of a mist, due to its pressure coming down from 800 bar to atmospheric in a fraction of a second. If anyone approaches and comes within the vicinity of this mist / spray, he will immediately be subjected to third degree burns. The temperature of the mist will be much higher than the heat given to the HFO (140 deg C) due to the pressure increase - after fuel pump - to around 800 bar.

Moreover, all the exhaust pipes being hot, an immediate fire can result.

The first two actions should be to 

1. Stop the FO Booster Pump and FO Circulating Pump.

2. Inform Bridge and stop the Main Engine.

In the old days, these pressure pipes were merely thickly lagged.

Luckily, modern engines have double skinned pipes, where, if the internal pressure pipe was to rupture, the outer skin seals it off from being released into the vicinity. Instead, the fuel oil accumulating between the two skins drains down via pipes and is led to the Fuel Oil Drain tank. A High Level Alarm fitted in the tank warns the Engineer of impending trouble.

Then there are the various smells from the galley, which comes through the blowers, reminding you of what’s cooking. This is mainly on older ships, where there were no Engine Control Rooms. 

(Reminds me of an incident on this same ship, the ‘Chennai Sadhanai’. I used to regularly check the galley for any electrical faults, so that I can inform the EO to repair same and also check for any accumulation of oils and fats on various surfaces, as they can be considered as fire hazards. On one such occasion, I mentioned to the Bhandari - the cook for the crew - that I can smell his morning parathas in the Engine Room every morning. After that, he promptly made it a point to send down - to the ER -  a plate of hot parathas and some ‘sabji’ at 6 every morning. I can still taste it).

Getting back to smells, different oils smell differently when burning or heated to above normal temperatures

Hydraulic oils at high temperatures have a recognisable odour.

So does Main Engine Lubricating Oil, easily recognisable after 60 deg C, especially if one has taken cognisance of the Lub Oil Purifier when in operation.

Which brings me to my topic, “Smells and Thrust Block”.

For some of the readers, this incident may be old hat, as they may have read about it in one off my "Marine Musings" a year or so back. Since the incident had been dealt with rather scantily at that time, I have, once again, taken it in hand and, the incident being rather complicated, have laboured over it and elaborated and embellished it, to include all that was in my memory. The long and the short of it is - I have rewritten the incident.

The lecture on 'smells' is a case in point.

The "Chennai Sadhanai" was my last Sisco ship. (This was the first generation of “Chennai” ships and not to be confused with later ones bearing the same names). As such, I carry very fond and pleasant memories of that ship, even though a life threatening explosion and a massive fire took place in the forepeak store and a rare type of damage took place on the Main Engine.

I was the Second Engineer. Having no ‘UMS’ those days, we were keeping normal watches.

Good people, good camaraderie and a hard working, happy crew. Throw in good weather (mostly), blue seas full of flying fish, dolphins, an occasional whale, the inspirational beauty of the variety of sun rises and sunsets, going past the Great Barrier Reef and, on occasion actually seeing the Reef in all its beauty - it was contentment for the soul.

Time, at times, flew. At times, it weighed heavily on my hands.  Technical books and Instruction Manuals became my companions, preparing for the forthcoming Chief’s exams. Each sunrise and sunset was more beautiful than the one before. My mistress, the Sea, was in her myriad moods and I exulted in her arms. I was at peace with the Cosmos.

It was into this tranquility that I was thrust into one of the very rare types of breakdowns that a Main Engine can suffer.

One day, while on the early morning watch, I smelt burning oil. Following my nose, I noticed slight wisps of smoke - hardly discernible unless you went looking for it, it was so little - coming out of the Michell Thrust Block, from between the shaft and the seal ring.

I found a little bit of smoke issuing out of the Forward  and Aft ends of the Michell Block shaft seals. I immediately reduced rpm and felt around the Thrust Block, but found no evidence of overheating.

I called the Chief Engineer down and showed him. On increasing the rpm, smoke was again seen issuing out after a while.

We stopped. We were well away from land, so there were no extraneous dangers.

The small opening for taking clearances was not large enough for a visual inspection.

Unlike modern engines where the thrust block is encased inside the after part of the engine proper itself, this thrust block was located outside the engine. The principles of operation are the same. The method or path of lubrication is slightly different. 

On modern ships, oil gets continuously sprayed, through nozzles, on to the thrust pads and thrust face and drains down directly in to the Main Lubricating Oil Sump. 

On ships with the Thrust Block located outside the engine, the initial stage of lubrication is the same, through nozzles. The difference is in the draining of the oil after lubrication, where the drained oil collects in the bottom of the box-like Michell Thrust Block, after which a drain pipe leads the oil into the Main Lubricating Oil Sump.

An Engineers’ view of the Thrust Block

The top cover was opened to check.

All ahead thrust pads were heavily scored, with all of the bearing metal missing as well as a bit of the base metal of the thrust pad. If the damage had been limited to only the thrust pads, we would have been fine as, then, it would have been only a matter of renewing the Pads.

Spare Thrust Pads and accessories

The bad news was that the Forward side of the Thrust Collar on the shaft, which takes up the full thrust of the ship when the ship is moving ahead, was badly scored. This Thrust Collar, at the time of manufacture, is precisely machined and is machined to a smoothness that beats the softness of a baby’s bottom.

Even worse, the shaft had taken a permanent shift forward by 8 mm, which more or less corresponded to the 10 mm white metal bearing coating on the Thrust Pads that had been wiped out.

At this time, we checked all the Connecting Rod Bottom End sides, to ensure they were not rubbing against the webs. We were lucky. If the shaft had shifted another 4 mm, due to heavier damage to the Thrust Collar and more of the base metal of the thrust pads wearing away, we could have had rotating parts rubbing against the webs, causing extreme hot spots and, likely, a crankcase explosion.

A Thrust Block is designed to take up the axial forces transmitted by the Propeller and distribute it to frames in the Engine Room constructed for this purpose.

In yesteryears, the Thrust Block was a separate unit placed aft of the Main Engine and had a bypass feed of Lubricating oil for its lubrication. From the 1980s onwards, almost all designs had the Thrust Block within the Main Engine frame and as an integral part of the Engine, sharing the pressure of the Engine’s Lubricating Oil system.

Diagram of a typical and simplified Michell Thrust Block located outside the Main Engine – Thanks to You Tube and DG E Learning ADU Academy.

This is exactly what we had on the Chennai Sadhanai. Although it looks simple in the diagram, it is rather complicated, because each pad was a ‘tilting’ pad. Removal and replacement of the thrust pads is difficult, requires skill and precision and an understanding of the working of the Thrust Block.

Nearly similar to what we had. Copied from ‘Machinery Lubrication’

By Heinz P. Bloch

The Ahead Pads were badly damaged. But we could not take them out as the shaft had shifted forward and had jammed the Thrust Pads. So we welded two steel supports on the tank top close to the intermediate shaft flange, fitted two hydraulic jacks and jacked the shaft aft. This loosened the jammed pads which were then removed.

So, it was a succession of tasks - jack the shaft aft, remove one pad, release the pressure in the jacks, turn the shaft slightly using turning gear so the next pad can be removed - repeat process.

To smoothen out the grooving on the Thrust face of the Thrust Collar, we used disc grinders and different grades of files to file the grooved Thrust Collar, turning the shaft on turning gear simultaneously. After quite a while, we achieved a degree of smoothness which we thought would be sufficient.

Meanwhile, we found the cause of why the Thrust Block failed.

The Michell Thrust Block of those days had a sump at the bottom where the lubricating oil falls after doing its job of cooling and lubricating the Thrust Pads, Thrust Face. This Lubricating Oil that falls into the sump is drained by a drain pipe located about 50 mm above the bottom plate of the Michelle Thrust Block sump. So about 50 mm of oil always remains inside. Over a period of the last 9 years, this remaining oil had turned into sludge and partially choked the 60 mm drain pipe. The sludge slowly got splashed on to the pads and collar, causing fine particles to get lodged between the pads and the collar, resulting in grooving.

The white metal of the pads, being the softest metal, sustained damage first, transmitted the damage little by little to the Thrust Face and slowly worsened. The damage to the Thrust Pad damaged the Thrust Collar which, then, damaged the Thrust Pads more. The damage was, thus, cyclical, Once metal to metal contact occurred, smoke emanated from the block.

We used the spare set of Thrust Pads, fitted after a thorough cleaning of the bottom of the Block and flushing out with copious amounts of fresh lubricating oil. The pads were fitted, the block assembled and the jacks removed. We slowly increased the rpm and ran at “Full Ahead” rpm of 60 for nearly a day.

But the new pads also got damaged, as we were not able to achieve the low ‘micron’ finish that was needed, with the rough tools that we had.

We were back to square one. 

The ‘Astern’ Pads and the ‘Astern’ Face of the Thrust Collar were undamaged.

So, we tried steaming astern. After six hours, we had made no progress.

The only alternative was a tow by a sea going tug. The Company arranged for one, which reached after a 3 day wait. A ‘messenger’ rope from a Line Throwing Apparatus shot accurately brought a thin line, then successive thicker varieties of ropes and finally two thick wire ropes, all handled by winches. After tying the wire ropes, the tow began.

I am not aware of what was the agreement for towing between our Company and the Towing Company. Sometimes a Lloyds Open Form is used.

We were towed at a steady 6 to 7 knots and finally made it to Japan.

A Japanese workshop came, dismantled the Thrust Block, machined the Thrust Face of the Collar using a tool holder that went round and round the shaft (in situ machining), fabricated a ring which was screwed on to one end to compensate for the 8 mm of machining done on the Collar (to obtain a smooth, low micron finish) and the axial shift of shaft, assembled everything and, after an Engine trial, left. All this took 3 days of continuous work.

It was precision machining at its best, achieving the micron finish that even a baby’s bottom doe not have.

This - the accumulation of sludge and the particles from the sludge coming into contact with the Thrust Pads and the Thrust Collar - cannot happen in modern engines as the Thrust Block is located within the Main Engine frame with the Thrust Block access door looking (more or less) exactly like any of the other crankcase door - the last in the series. Moreover, the lubricating oil that is sprayed through nozzles falls into the crankcase floor and the gratings allow it to fall / drain further into the Lubricating Oil Sump. There is no accumulation of oil beneath the thrust block.

The Fleet of the Company, being all sister ships, the others were intimated to carry out a check of the Thrust Block and clean its sump forthwith.

To think that a ship had to be towed, where it had all started with the smell of burning lubricating oil.

Smells are important.

To me, the various smells of the Engine Room were aroma.

A. Ranganathan