BLOG 78 - Dry Docking at Verolme - Propeller Repairs - "Tip of the Day"

(The first paragraph is a repetition, for the sake of continuity).

What did Happen on the Bridge?

While waiting for the Office to call back, Captain Abraham 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.

The Pilot wanted a ‘Full Astern’ movement.

Being a ‘Right Handed’ ship, with an astern movement, the bow tends to swing to starboard. (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 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”.

The Duty Officer heard it 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

Chain used to anchor 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.

Chapter 8:

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 a Pilot on board. The Pilot was an experienced ex-seafarer and he cooperated 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. After about 3 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.

Arrangements Astern on a Car Carrier

Stern View with Ramp Up

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 them all 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.

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.

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

We slowly made our way to Rotterdam and Verolme Docks.

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

This being the ship’s first 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, 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, 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 closeby 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.

Tip of the Day:

One of the methods of checking the balance of shafting and propeller at sea is to make a broad and 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.

===== Continued in Blog 79 =====