Blog 135 - "Marine Musings" - When a Prop meets a Buoy

What Happens When A Prop Meets a Buoy

About _Propellers - Nosac Taishan - Antwerp Incident

Some of you may have already read a substantial portion of this in a previous blog. This narrative has been revisited, has been embellished, redecorated, ornamented, garnished, varnished and, if I may add, dressed up.

(I intend holding a dart board in front of me for the darts that will surely thrown).

Beauty is in the eyes of the beholder.

The ‘Nosac Taishan’ was a brand new ship, built in Sumitomo Yard, Oppama, Japan. As Owner’s Representative, I was in the Yard 3.5 months before she was delivered and, therefore had to familiarise myself with  every aspect of her, from stem to stern. 

I was its first Chief Engineer when we sailed out.

To many, she was big box that went sailing, with a hideous stern.

To me, she was a beauty, her lines visible to me, her stern and stern ramp lending an elegance to her lines.

On her maiden voyage, she breezed through several US ports, to the awe of all and sailed across the Atlantic, to load, to discharge.

Le Havre, Zeebrugge, Antwerp, Rotterdam, Bremerhaven and Gothenburg were some of the ports we had to call during that European leg.

Europe was a madhouse. Short runs between ports, long pilotages up or down river, short stays of just a few hours, docking and undocking at any time of day and night with reduced crew meant sleep deprived staff. 

The vessel schedules were normally to sail after 3 or 4 hours, after discharging 200 odd cars and loading 200 odd cars.

As Chief Engineer, I would be called at ‘1 hour notice’ and would join the Duty Engineer and the Duty Motorman in the Engine Room within 15 minutes. The maximum hours of sleep I would have gotten was 2 to 3 hours, before being woken up. The Electrical Officer and I would be the maximum affected as we both have to be in the Control Room. The Second and Third Engineers would relieve one another.

The Main Engine would be on ‘Bridge Control’, but I would be keenly watching to see if all the sequences were taking place as programmed. I would imagine myself as something akin to the Director of Operations at NASA during a launch.

One of my core duties is to ensure that the Engine is not stressed at any time. The most prominent of these stresses are Heat Stresses caused by a sudden decrease or increase in operating temperatures. Modern metallurgy has improved to a point where  materials operating at high temperatures are resilient to a certain degree. But if subjected to frequent steep temperature gradients, they are likely to crack, much like a human mind under strong, frequent stresses.

Without going into too much detail, suffice it to say that speed reduction, in small steps, from full speed to manoeuvring speed is one of the essential operations to minimise heat stresses. It was important for me to remotely watch this reduction of speed by the Bridge operator and, if necessary, override the Bridge and correct the rate of reduction by taking over controls from the Bridge to Engine Control Room.

This ship was captained by a top class Captain, who understood well the nuances of operating the Main Engine. But I have sailed with mavericks who used to think of the engine as a horse and, when going at full speed, pull hard on the reins to stop the horse. Maybe they were under the impression that, as the Main Engine power is expressed in “horse power”, it is actually a horse.

Those were the days when I used to walk straight up to the Bridge and, after ascertaining that there was no emergency, would quietly tell the Captain that if the same thing happens again, I will have to take controls back to the Control Room. The explanation from them would be that the previous Chief Engineers had no problems with such speed reductions. (I would have just joined the ship). Then I would take the opportunity to explain to him in detail why it was harmful to the Main Engine.

We were entering Antwerp around midnight+. To get to the berth, we have to go through one of the two locks and berth close to the locks, upriver. I am not certain if we were going to discharge or load or both.

We were well outside the locks. Captain Ab was on the Bridge, along with other watchkeepers. I was in the Engine Control Room, along with the EO, the duty Engineer and a Greaser.

The Bow Thruster was running and in use. All 3 generators were running, which is normal when using the Bow Thruster. I was watching all the parameters.

We were on Bridge Control. A ‘Full Astern’ movement was given. Less than a minute into the ‘Astern’ movement, I heard the ‘humming’ sound of the Engine change to one of strain. I looked at the Load Indicator and realised that the Engine Load had gone up by more than 50% of what was normal for that movement.. The engine was straining to give the required rpm and the Fuel Index was increasing more and more. A ‘Stop’ signal stopped the engine.

The changes in parameters had taken place in the space of 10 to 15 seconds.

My first thought was that we had run aground. I called the Bridge.

I was told that we were in the locks, which meant at least a 20 minute period of non-activity. I went up to the Bridge and spoke to Captain Abraham about the rapid and sudden change in parameters at exactly a particular minute and second. Since we had not run aground, I stated that I suspect propeller damage.

He said that, due to a wrong ‘Astern’ movement from the Pilot, the vessel may have struck a navigational buoy, as he had seen it drifting away.

Then the Agent, who was at the pier waiting for the ship to berth, was contacted for an immediate inspection of the propeller by an authorised diver.

In the meantime, I quickly called all Engine Room personnel (this was probably around 0130 to 0200H) and formulated a check list of all important inspections to be made of the Main Engine, in the short time available alongside.

The inspections included

If turning gear motor amps had increased - Negative

Thrust Block inspection - Normal

Bearing clearances - Normal

Any longitudinal shift of shaft - None found

Chain inspection - Normal

If possible, crank web deflections - Not done, no time

Air Coolers Check - Normal

The sound from the turbochargers had already been checked, found no undue vibrations, oil levels of the BBC Turbochargers’ sumps all good, LO pumps good.

I had a 'Check Main Engine Fuel Pumps' Timing' on my list, but did not have the time to check it.

We had less than three hours to carry out umpteen number of checks.

In the meantime, the diver had come up and he reported that all was fine with the propeller. I asked him how many blades he had checked. He said he had checked four blades.  I took him down to the Engine Control Room and asked him again if he had checked properly and was he sure there was no damage. His reply made me lose my temper. He had said, with a very racist sneer, “ Chief, if you had wanted me to give a ‘damaged propeller’ report, you should have told me before I went down”. I was furious.

I then showed him the propeller drawing that this was a 5 bladed propeller. He had already typed out his report but he had not mentioned the number of blades. He quickly changed his previous verbal statement that he had checked 4 blades and corrected it to 5.

I refused to sign the report and told him to get out of the ship. Apparently, he went to the Agent, who signed the report and handed it over to the Captain. The report, without my signature, had no value.

By then cargo had been completed, we picked up the ramp and went out through the locks.

As we went to ‘Slow Ahead’, I noticed that the Load Indicator showed 30% more than normal. On reaching ‘Half Ahead’, the Load was 60% more than normal. ‘Full Ahead’ showed about 80% increase in load, along with a ‘thwack, thwack’ coming from the stern tube and heavy vibrations of the engine and hull, with the turbochargers starting to surge..

We reduced to slightly less than ‘Half Ahead’, so that the noise reduced and the vibrations were tolerably less. We changed Engine Controls to Control Room and tried to increase speed, with the same result. We even changed to Emergency Local Controls - where the pneumatics and hydraulics were cut out and controls reverted to pre-automated days (like I had on the “Chennai” ships) - and tried, all to no avail.

If we were to keep the schedule, we would not be able to sustain running at this low an rpm for long.

I drafted a message to be sent to the Hong Kong Office. The Superintendent was different from the one I had a verbal fight with. We called them on the ‘Inmarsat’ after a few minutes. They said they were assembling a team at the conference table and would call back.

What did Happen on the Bridge?

While waiting for the Office to call back, Captain Ab gave me a step-by-step account of the incident when the buoy was found drifting away.

He and the Pilot were on the Bridge  Wing, with the vessel being aligned for entry into the locks. Because of the span or beam  from Bridge to Bridge wing being large, the Captain always used the handheld radio to communicate with the Duty Officer, to pass on the Pilot’s instructions, either for Engine Telegraph orders or Helm orders, the Duty Officer at the  Engine telegraph and the duty AB at the wheel.

On this ship, like most Car Carriers, the Bridge was right forward, so you had to go out on the wings to see astern. Unlike on other ships having the Bridge near the stern and above the Engine Room, one cannot hear or feel an engine start, unless one is watching the rpm indicator closely.

Arrangements Astern on the “Nosac Taishan, with the Stern Ramp Lowered”

Arrangements Astern on the “Nosac Taishan’ with the Stern Ramp Raised.

Note the Position of the Bridge Forward

The Pilot wanted a ‘Full Astern’ movement.

Being a ‘Right Handed’ ship, with an astern movement, the bow tends to swing to starboard and the stern to port. (A link to a brief but interesting video is below).

https://youtu.be/y7-tUlxr_no

Seeing a buoy very close to the ship on the port quarter, the Captain refused to transmit the order and told the Pilot that the request for “Full Astern” will be given once the vessel clears the buoy. The Pilot, probably with racial prejudice, started screaming at the Captain, shouting “Full Astern” “Full Astern”, whereas the Captain was calmly telling him “There is no cause for alarm. You will get the astern movement after we clear the buoy”.

The Pilot shouted even louder “Full Astern”.

It will be pertinent to note that there were two tugs tied to the vessel to align her to the locks.

The Duty Officer heard the Pilot screaming “Full Astern” and, thinking it was legitimate, gave the “Full Astern” movement.

About 30 or 40 seconds later, feeling a bit of vibration - an ‘astern’ movement is always accompanied by vibrations - the Captain saw the vessel starting to swing to starboard and, looking up at the rpm indicator on the Bridge Wing, realised the Main Engine was running on ‘Astern’, called for it to be stopped.

Looking astern, he saw the buoy drifting away.

The rotating propeller had cut the anchor chain of the buoy, damaging itself.

Anchoring a Buoy

A View of the Buoy from Below

All propellers are balanced. This ship had a highly skewed 5 bladed, lighter than normal, high precision balanced propeller. The slightest damage to it will cause vibrations and cause engine imbalance.

Trying to Convince the Office Pool that our Propeller is Damaged

The call from Hong Kong came through. We were still going down river, with the Pilot on board. The Pilot was an experienced ex-seafarer and he co-operated with us to the utmost and had a very avid interest in what was going on and the damage sustained.

Both sides, Hong Kong and the ship had their speakers on. They first spoke to the Captain, who handed the phone over to me.

There were six people at their conference table. They immediately started bombarding me with different questions covering so many angles that I started getting confused, trying to jump from one answer to the next, without any coherence. After about 2 minutes of struggling to answer their questions coherently, I told them all “Before you ask more questions, let me give you the sequence of events, why I suspect the propeller is damaged, why I am sure everything with the engine is fine and what checks I had made on the Engine to ensure that there is nothing wrong with the Main Engine. Would you all be willing to listen without disturbing me? I will answer all questions at the end.”

There was quiet for nearly a minute at the other end and then a quiet voice said “Go ahead Bada Saab”.

I had my notes-in-brief ready. I gave them an exact run down on the sequence of events, before and after the change in parameters and what the parameters were that changed and what they were under normal circumstances. I then went on to tell them what all had been checked on the Main Engine and what were the findings.

I continued with why I felt that the Diver’s Report was falsified, with the Agent and the Diver having colluded, so that the vessel is quickly despatched out of the Antwerp Agent’s jurisdiction. I finished with why I was certain that there was damage to the propeller. I think I must have spoken for 12 or more minutes.

There was silence at the other end for a couple of minutes. When the silence extended, I said “Hullo, is anyone there, or have I been taking into the ether?” There was some laughter from the other end and somebody said “No, no, we are all here and digesting what you had reported. Please wait”. Apparently they were conferring - after all it was a Conference Room - with the phone covered.

Another two minutes or so, they came back and one of them said “Ranga, we do not have any queries on your checks. But you are asking us to make major and costly decisions based on your instinctive observations. How can we make sure?"

I had already prepared an answer to that question. “We definitely will not be able to go faster than what we are doing now, which is just below Half Ahead rpm. It is now 0530am here. We are on pilotage down river. Let us find a convenient place and anchor. Let us get Class, P&I / H&M and another good, authorised, diving company - all together - and let them inspect. After that we can make a decision”.

That seemed the sensible course of action to all.

They then asked Captain Abraham to anchor and await Class Surveyor, P&I Surveyor and Diver.

The Pilot, who had been listening in with interest, was already at the chart table and suggested a good area to anchor.

We anchored about half an hour later.

Whether it was the same day or the next, I am unable to recall. All 3 parties turned up around the same time. I took them down to the Engine Control Room and showed them all relevant drawings, mostly restricted to the rudder, propeller and stern frame.

In design, the stern of Car Carriers, RO-Ros and Super Carriers are quite different from a conventional ship, because of the presence of a Stern Ramp.

What is the effect of a skewed propeller over a conventional one?

After years of experimentation, analysis and sea trials, it was observed that aptly skewing a ship propeller nullifies or considerably minimises the extent of unsteady hydrodynamic loading in this flow field. This indirectly has positive effects in reducing resistance due to viscous 'drag' effects.

What is a highly skewed propeller?

A marine propeller whose blades are in the form of scimitars, typically with the tip of one blade aligning radially with the root of the following blade.

A 'Skewed' Propeller Blade

Above image is the closest I can find of what we had on the ‘Nosac Taishan’ - thanks to ‘Slideplayer’

I explained to the Diver and Surveyors that it was a ‘highly skewed’ propeller and how it should look. I also mentioned that it looks like a flower, with its 5 petals just opening (as seen by me in the Shipyard).

We went down to the diver’s barge, where the diver had all his equipment, including a video monitor and a 2 way radio set.

The river water was a little murky, so the diver could not get a long shot of the full propeller. As he moved closer to each blade, he pointed his video camera at the blade edges - we saw the tip was bent quite  a bit on one blade, the bend of the blade tip decreasing ever so slightly, but visibly, on the following blades. All the 5 blades had sustained damage.

The diver, on coming up, told me “Chief, you described the propeller as a flower. On seeing this propeller, I could well imagine it looking like a flower - but now it is looking like a cauliflower”.

The Classification Surveyor was relieved and immediately recommended docking the ship, with further checks to be made on the tail shaft along with repairs to the propeller.

A representation of a bent propeller blade

In the meantime, the Hong Kong Office had been scouting around for an available dry dock in that vicinity, on the grounds of my dialogue and taking a ‘worst case scenario’ reaction. They found space in Verolme Docks, Rotterdam.

Map showing Antwerp and Location of Verolme Docks

From Wikipedia (I think it was this very same dock that we went to)

We slowly made our way to Rotterdam and Verolme Docks.

This being the ship’s maiden docking, there was plenty to prepare and keep ready. There were 2 ship’s side sea valves that were not functioning and which required  change. Apart from that, it was mainly to do with revising how to get shore power supply, how to get cooling water supply for AC and Fridge plants and other routine dry dock matters.

Surprisingly, only four of us, the Captain, the Chief Mate, the Electrician and myself had ever seen dry docking of ships.

The Superintendent, a new entrant to the Company, but experienced, had flown in to Rotterdam.

The ship entered the graving dock, the gates were closed and the pumping out of water commenced. Much before she sat on the blocks, the first blade of the propeller gradually came into view.

The Superintendent and I were dockside, he with binoculars from the Bridge. He seemed very anxious, kept asking me “What if there is no damage to the propeller?” I kept reassuring him that I am certain that the propeller is damaged, being at the same time bemused and a little irritated that they still did not believe a Chief Engineer (especially one who knew the ship very well), nor a Class reviewed Diver's Report.

Blade thicknesses vary, with the maximum thickness at the root of the blade and gradually lessening as it reaches the tip of the blade. The blade thickness of highly skewed propellers is considerably lesser than conventional four bladed propellers and, hence, lighter in weight. All these add to a smooth performance, with very little or near zero vibrations.

The water levels in the graving dock reduced. As more and more of the top blade became visible (# 1 unit had been kept at TDC), it was easily seen that the blade was bent inwards. As the other blades came into view, all 5 blades were found to be bent to varying degrees.

We were lucky in many aspects.

Regulations state that propeller repairs can be carried out only if the damage is located beyond 0.7 R from the root. That is 30% from the tip. The worst damaged blade was 24% from the tip. Permission to repair was given by the Class Surveyor. If it had been more, the whole blade would have required replacement or else the whole propeller would have needed renewal. Renewal of the propeller would have meant flying in the propeller from her sister ship (“Nosac Takara / Tancred?) then in Sumitomo Yard, nearing completion. The other alternative was to use the cast iron spare propeller on board.

The shipyard people removed the propeller.  This was a Kawasaki manufactured propeller. But they did not have any repair outlet in Europe at that time. The best propeller repair workshop close by was LIPS, later bought over by Wartsila.

It is really unfortunate that I was not a camera buff in those days - those photographs of the repairs would have been wonderful. Today (2022), I am still not a camera buff, but have no need of a camera since most of everything is available on the Internet.

We were in the dry dock for 10 days. The propeller was in the LIPS workshop for 7 days. I attended the propeller repairs for 5 days and watched what they were doing.

Having the full set of propeller drawings, they first took all measurements and compared with the original. Then they checked the entire surface of all the blades for cracks. None were found in the 0.7R area.

The LIPS Foreman told me that this was the first blade to hit the anchor chain of the buoy, followed in sequence by the others, the bending damage being most prominent on the first, with the bend damage gradually reducing.

Then the job of straightening the bends started. Using massive gas torches, the surface around the bends were heated evenly and, using massive hydraulic pincer-like tools, the bent sections were straightened out. Then they moved on to the next one. Once the blade had cooled, it was subjected to a crack detection test. 2 of the blades had frayed at the tip, so they had to be ‘trimmed’, after which the other three were also trimmed. Constant measurements were taken to ensure that they were conforming to manufacturer’s dimensions.

I am not sure, but I think ‘annealing’ was done at night, one blade at a time.

After completion of all work, it was subject to static balancing.

From Ricepropulsion.com (Representation only)

https://youtu.be/HLL4CXf1PAE

Ship propeller blades balancing control

Then it was finally polished and sent back to the Ship Yard for assembly.

One of the methods of checking the balance of shafting and propeller on board is to make a long and slightly broad visible mark on the Intermediate Shaft and check if the shaft returns to the same position after each start. Ideally, it should not return to any spot that you may have marked.

Assembly took place and vessel sailed out to complete all the ports on her European schedule.

It was an interesting and uncommon experience. Why I have elaborated the whole incident is to interest the sailing Engineer to

1. Become thoroughly familiar with normal and existing parameters, so any anomaly can be spotted quickly.

2. Stay calm. Do not panic, as panic will distort your thinking processes.

3. Analyse and check.

4. Keep a record - short notes - in your pocket diary.

5. Do not be overwhelmed with the Managers reactions, as they will possibly be close to ‘panic’ mode.

6. Insist on taking over the dialogue, using your notes.

7. Be courageous - Class is always there to help.

AR