Ph: F.Parisi

The Wind

John GattiBy John Gatti22 Febbraio 202112 Minuti

The wind

Every port presents its own difficulties.

With some, it can be fog that creates complications; with others, it’s the wind, the current, confined spaces or particularly shallow water and so on.

It can be the combination of several of these elements that together present greater risks for ship manoeuvring.

Today we are going to talk about the wind.

Even though the wind can sometimes help, when it is particularly strong, you need to make careful assessments; otherwise, you risk not being able to manage this force, which can put you in difficulty.

I said, “the wind can help sometimes”: I am referring, for example, to those situations in which a light wind can help to push a vessel away from the quay during unmooring; or, similarly, when a light breeze gently accompanies us to the quay. The wind blowing from the right direction and a length of chain on the bottom can allow us to rotate a ship on itself without the aid of the engines or thrusters; again, a well-calculated wind, with respect to the shape of the sail surface, can facilitate a favourable approach or a departure.

Another aspect that is not often considered, which is also interesting, is that the wind often helps the pilot in the “preparation” of the manoeuvre. In fact, in the phase of discussion with the ship’s captain, one of the most delicate points to discuss regards the eventual number of tugs to be used during the operation. The dangers posed by wind and current are often compared, but the wind is perceptible and visible, whilst the more subtle current can also be accompanied by optimal weather conditions. It goes without saying that it’s much easier to convince the captain when he can hear the wind whistling and see the sea streaked with white in respect to discussing an invisible danger lurking beneath the surface of the sea.

In this regard, an event that happened several years ago comes to mind:

Four days of strong sirocco accompanied by overcast skies and rain showers were followed by a series of perfect days from a weather and sea condition perspective: clear skies, calm sea and no wind.

Here, the breezes that blow from the East and South-East bring a wind-driven current into the channel and the longer the winds prevail, the stronger the current becomes.

During this particular event, the water flow that fed in from the East and vented to the West was particularly violent. This was a strong current, but for the first two days, at least was still predictable … the anomaly was represented by the fact that this wild force continued vigorously and invisibly under the sea’s surface on the third and fourth day, even though the weather continued to be ideal. 

It was hence difficult to convince captains of the importance of using tugs to contrast the situation.

Back in those days, the pressure exerted by shipowners to rein in expenses led captains to try to save money “in all circumstances”; on the other hand, pilots may have exaggerated the gravity of a certain situation a little so as to “at least get something”.

But this time, the situation had reached the limit: the captain saw a beautiful day, and there were no words that could convince him of the danger of the situation. Besides, we too expected the usual downsizing of the current in a short time.

In short, three ships during manoeuvre passively collided with the same moored vessel in the space of three days, which was unfortunately moored in the wrong place as far as the concerning the river’s protruding undercurrent was concerned.

I was on the fourth vessel on the fourth day …

It was an excellent ship: 150 meters long, with two engines and a bow thruster. It was in a “half load” condition, ideal for manoeuvring. The captain was a regular at the port; he had been coming twice a week for years and was very familiar with “dynamics and situations”.

As soon as I got on board, I made him aware of the previous days’ incidents and the anomalous presence of this strong current. A patronizing look was the conceivable reaction. I tried to insist, but the reasoning that he used had solid foundations: 

  • the ship manoeuvred well;
  • the captain, who knew the port well and had a great experience, did the manoeuvre himself and, usually, did it well;
  • it was the fourth day of good weather, and the current was bound to be less strong than when the other incidents had occurred.

I was not convinced, but anyway, I could not assert myself, also because, deep down, I too thought that, if he set the manoeuvre up well, he would be able to manage the situation.

The discussion did not end well from a psychological point of view: on the one side, there was me, the pilot, defending my position, and on the other, there was the captain who was dying to show me just how good he was, even in that difficult situation. In other words, we had not reached a common viewpoint, which would have been the basis for a shared manoeuvre.

Under normal conditions, you would reach the point of manoeuvre at a decent speed, stop the engines in time, decisively reverse the left engine, the bow to the left, and the ship would rotate, almost in a skid. At the appropriate moment, the starboard engine would also be reversed, and you’d be done.

This time, thanks to the psychological defect of our discussion, in order to demonstrate his skill to me, we reached the end of the channel at an even faster speed than usual. The more I told him that we were going too fast with that current, the more he would send me messages with his eyes, looks as if to say, “now I’ll show you how to do it”.

Everything seemed to be going well up to three-quarters of the way, but when the hull of the ship’s left flank began to close until it was oblique to the current flow, the situation worsened.

The ship began to go down, keelwards quickly.

When the captain hesitated, I intervened, suggesting that the engines be put in reverse and the bow thruster to port. The aim was to collide whilst the vessel was stationary to avoid causing hull breaches; we collided three times, recovering space behind on each rebound. We managed the engines to touch as gently as possible and always when stationary. Eventually, we managed to get out of the current and reach the mooring. 

The material damage was not particularly serious, but the damage to my pride, for not being able to impose my opinions, and to that of the master, owing to the consequences of his presumption, left their mark on us for a long time.

Ph: J.Gatti

But let’s get back to the wind.

Experience has an important part to play in this case too.

The differences between ships are not limited to classification by type nor size. The same ship, in fact, has completely different characteristics depending on its draft or the load it has on deck; and the same manoeuvre, with the same ship, under the same conditions, can be influenced by unexpected obstacles or by differing weather and sea conditions.

Experience leads to unconscious and automatic analysis of numerous variables, which results in awareness of the necessary precautions for manoeuvring.

Obviously, we must maintain an absolutely satisfactory safety margin.

Where this margin becomes affected or when experience is insufficient, it becomes necessary to support our feelings with calculations. Many mostly practical formulas can come to our aid to establish wind force in tons.

Some offer the possibility of calculating this force based on the angle of incidence of the wind, and others also consider the density of the air. Here I propose a simple formula to apply that still offers reliable results:

Wind strength (Ton) = Wind speed squared in metres per second, divided by 18, times the exposed sail area in square metres.

Consider, for example, a 366-metre-long container carrier with an 11-metre freeboard loaded with five rows of containers along its entire length. 

What strength will the wind have, in tons, blowing across it at 25 knots?

25 knots correspond (more or less) to: 12.5 m / s

The surface of each container is: 2.4 m x 5 =   12 m

Therefore, the total sail area is:

(11 + 12) x 366 = 8418 sqm

Wind strength at 25 Kn = (12.5 × 12.5) x (8418): 18 = approx. 73 Ton 

If you have the latest 70-ton tugs available for the manoeuvre, it is advisable to use at least three in these conditions.

I will stop here, aware that this topic deserves to be studied in a lot more detail.

However, we plan to dedicate an entire course, both on our site and on seably.com to the wind and the secrets it holds.

Ph: J.Gatti

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