M.V. Weybank - Chapter 15
The TC tracking chart is shown once again below.
In the text boxes in the southern hemisphere in the chart above the tropical cyclones are all denoted as Tropical Cyclones no matter whether they are in the southern Pacific Ocean, southern Indian Ocean or South Atlantic.
The text boxes in the northern hemisphere are labelled either as Tropical Cyclones, Hurricanes or Typhoons but Hurricanes and Typhoons are just regional monikers. They are all the same thing – Tropical Cyclones. So, are Tropical Cyclones the same whether in the northern hemisphere or in the southern hemisphere? The answer is no, mainly due the Coriolis effect, the spinning of the Earth around its own axis.
Tropical cyclones derive their energy from the warm tropical oceans and do not form unless the sea-surface temperature is above 26.5°C. They are low pressure systems and have gale force winds (sustained winds of 63 km/h or greater and gusts in excess of 90 km/h) near the centre.
A Tropical Cyclone is born when hot moist air at the surface of the sea starts to rise rapidly – (like being in a lift in a skyscaper) and in doing so also sucks in warm air from around its base. When the warm air is shooting up the elevator, after a number of „floors“ it starts cooling down on its way as
it meets the colder air above it and this produces condensation – clouds start building up around the elevator shaft ( the „eye wall“) and these clouds can soon assume massive proportions. The whole „assembly“ (elevator shaft air and cloud formation) starts to rotate due to the Coriolis effect. In the northern hemisphere it spins anti/counterclockwise; in the southern hemisphere it spins clockwise. Providing the sea surface temperature remains warm enough it feeds the cyclone with energy causing the „beast“ to grow. The cyclone also starts rotating faster and this is what causes the gale force winds.
The gale force winds can extend hundreds of kilometres from the cyclone centre. If the sustained winds around the centre reach 118 km/h (gusts in excess 165 km/h), then the system is called a severe tropical cyclone.
The circular eye or centre of a tropical cyclone is an area characterised by light winds and often by clear skies. Eye diameters are typically 40 km but can range from under 10 km to over 100 km. The eye is surrounded by a dense ring of cloud about 16 km high known as the eye wall which marks the belt of strongest winds and heaviest rainfall.
To find out not only what the Coriolis effect is but just about anything else about cyclones/anticyclones/tropical cyclones/why the world‘s deserts are all located around either 30°N or 30°S/ and many other related topics, click on the link above. The article was written by a professor but unlike so many of his ilk he writes in „easy to understand“ English and has included many very good illustrations.
If you would rather download a PDF copy instead of reading it on-line, click on the link below:
Before returning to our meeting with Helene, two photos below show the difference in spinning direction between a northern hemisphere TC (hurricane Fran spinning anti-clockwise towards Florida) and a southern hemisphere TC (severe tropical cyclone in the southern Indian Ocean spinning clockwise).
At sea even under what could be termed as „moderate“ weather conditions, when walking around it could be a little bit like a clown‘s circus act, trying to walk in a straight line. If the ship was gently rolling, your brain could usually still manage to send you the right signals to keep you on an even keel. I once went across the English Channel on one of those giant passenger/car hydrofoil ferries when the weather was comparitively mild but when the hydrofoil stepped up the tempo it was impossible to walk like a normal human being. It was like walking across an earthquake, as if the deck you were walking on kept moving in all possible directions. It wasn‘t a violent movement, it just made you look silly like Basil in Fawlty Towers or like in a breakdance version of Irish dancing.
As Helene was rapidly closing in on us the Weybank started to roll, pitch and shudder. Anything that wasn‘t well battened down took on a life of it‘s own. The chair at my operating position in the radio room had a spindle hanging from underneath the seat which could be connected to a bolt on the deck. This spindle wasn‘t a tight rigid affair and couldn‘t clamp the chair to the deck. It just prevented you and the chair from sliding away when the ship rolled. By this time the „rocking and rolling“ of the ship had become so bad that the chair would zoom in some direction until the spindle braked the zoom but the chair would then pivot on one of its legs trying to catapult you into outer space. The answer to this was to rope your chair to anything that could stand the strain and you ended up like sitting in a spider‘s web.
By midday I couldn‘t stand it (sit it) anymore and staggered into the wheelhouse to see what was going on. The captain and all the mates were standing there hanging on for dear life. I looked at what they were looking at. Through the bridge windows I could see a wall of grey/green sea ahead that kept rising in height so much that I had to bend down to see if I could see the top of it when it rose above the top edge of the bridge windows. You could also feel the movement of the ship rising when suddenly the whole forward deck of the ship disappeared under a white boiling sea that smashed into the bridge/forward superstructure. We had just gone through the crest of the wave/wall and had started our downhill trip towards the next wall which was approaching fast.
During these mountain-climbing exercises the ship was also rolling and juddering which produced some weird metalic torture sounding acoustics. This crazy roller coasting lasted for hours on end. I do not know why but I had no fear, call it „Siebter Sinn“ (7th Sense) or whatever. I just knew that we would pull through, even when for a time things got even worse. We started to roll heavily and wedged ourselves into whatever could prevent us from being shot across the wheelhouse. When a ship starts rolling more than 20°, forget about walking anywhere.We all had our eyes glued to the inclinometer. This was a very simple but effective device that showed the roll of the vessel in degrees to port or starboard. It was in the form of a brass arrow that hung downwards from a spot exactly midship above the centre bridge window and underneath it was a brass semi-circular scale calibrated in degrees from 0° midship up to 45° port and 45° starboard. The scale wasn‘t calibrated above 45° for the simple reason that if the ship rolled more than 45°, Harland & Wolff, Belfast – the ship‘s builder obviously thought that the services of an inclinometer would no longer be required, the ship would have rolled over. A „Rolls-Royce“ inclinometer version is shown below.
You may not believe this but there came a moment when I watched the arrow moving through 35° starboard and then crept slowly up to 40°, hung there for a moment and slowly moved down again where it rapidly headed to port to do the same thing there. That was the moment when I started to wonder about my 7th Sense but luckily that was the only time that she rolled that far. At the time it happened even I was praying „please don‘t let the cargo shift“.
Every vessel has its own natural syncronous rolling period which is inversely proportional to the square root of the metacentric height and directly proportional to the beam of the ship. If the vessel encounters a series of waves in such a manner that the wave period matches the rolling, the vessel will have no time righting itself before the next wave strikes.
Another thing about rolling is when your own centre of gravity starts going somewhere else. For a brief moment you get the feeling of weightlessness, like the astronauts in training who were jetted up to the stratosphere, the aircraft then abruptly headed downwards again but at the point of transition from up to down they would experience zero gravity for a short time. Years later I was aboard a big container ship doing sea trials in the North Sea when we also started to roll heavily. There were a lot of sub-contractors aboard either there to get their equipment tested or as in my case to fix the radars if they decided to breakdown. I was in the bridge ( which was not just big but wide) when we took a bad roll to starboard and I watched in horror as one of the contractors standing at the port side lost his grip and flew like Superman right across the width of the bridge and smashed into the starboard bulkhead. He only survived because he didn‘t fly head first but he broke a lot of ribs and other bones. We had to interrupt the sea trials and sail back to where we could get him ashore to a hospital – this was in the days just before helicopter evacuations or pilots boarding via chopper became almost commonplace.
Returning to Helene she slowly lost interest in us as by nightfall we were climbing hills instead of mountains and although still rolling like a pig, nowhere near as bad as what we had already gone through. Slowly we escaped but high winds, rough seas and torrential rain dogged us for days after.
For those of you reading this but have not gone to sea, below is a YouTube link to give you an idea of what rough weather is like without even being in a tropical cyclone. I think the original footing came from a Disney film called „Oceans“:
I was long since well and truly in love with Weybank. It would have been perfect if she had been christened with a name like Sally or Mojiko but being a Bank Line ship I‘m sure she wasn‘t christened at all – just shoved down the slipway unceremoniously in Bank Line Owner fashion – like a whore being pushed out by her pimp – „get on with it and start earning your keep, you bitch!“
No champaigne, not even a bottle of Guiness bid her a „safe and happy …..and all who sail on her“.
Month after month she had carried us safely and uncomplaining through everything that nature could throw at her. Not once did we have to heave to in the middle of nowhere to change a piston, unlike aboard a number of other ships that I sailed on. You trust her with your life in the true sense of the word in the knowledge that she won‘t let you down. You even start talking to her like during the cyclone - „come on girl, you can do this easy“. I‘ve seen a lot of car owners who feel the same with their cars – are we all nuts? (yes).
To be continued…..