Ph: F.Parisi

The Wind

John GattiBy John Gatti22 Febbraio 202112 Minuti

The wind

Every port presents their own difficulties. 

For some mariners it is the fog that creates complications, for others it is the wind, the current, the confined spaces or shallow water.

For others, the combination of several of these elements may present an increased risk for their ship when they are maneuvering.

Today we talk about the wind.

Sometimes the wind can help, but when it is particularly strong you need to make careful assessments, or run the risk of not being able to manage this force, putting you in difficulty.

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

Another aspect not often considered, which is curious, is that the wind often helps the pilot also in the “preparation” of the maneuver. In fact, in the discussion phase with the ship captain, one of the most delicate discussion points relates to the number of tugs to be used during the operation. The dangers of wind and current are often comparable, but the wind is perceptible and visible, while the more subtle current can also be accompanied by optimal weather conditions. It goes without saying that convincing the commander when he hears the wind whistling and sees the sea streaked with white is much easier than when discussing an invisible danger lurking beneath the surface of the sea.

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

Ph: J.Gatti

Four days of strong sirocco, accompanied by overcast skies and rain showers, gave way from the perspective of the ocean-atmosphere, to a series of perfect days: 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 canal, and the longer the winds prevail the stronger the current becomes.

During this event, the flow of water from the river that moves from the east to the west was particularly impetuous. This was a strong current, but still predictable for the first two days … the anomaly was that even on the third and fourth day, though the weather continued to be optimal, the impetuosity of this force continued vigorously, and invisible to the eye under the surface of the sea. 

The difficulty is to convince the captains of the importance of using tugs to counter the situation.

Back in those days, pressure exerted by shipowners to contain expenses led the captains to try to save money “always and in any case”. On the other hand, there is the perception pilots might inflate the gravity of the situation by firing high to “get at least something”.

But this time the situation reached its limit: the commander saw a beautiful day and there were no words that could convince him of the danger of the situation. On the other hand, we ourselves expected the usual downsizing of the current in a short time.

In short, in the space of three days, three ships during maneuver nearly collided with the same moored ship which was unfortunately located at the wrong place with respect to the river’s protruding undercurrent.

I was on the fourth vessel on the fourth day …

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

As soon as I got on board, I made him aware of the incidents of the previous days and of the anomalous presence of this strong current. A smug look was the imaginable reaction. I tried to insist, but the arguments with which he replied had a solid foundation: 

  • the ship maneuvered well;
  • the commander, a good connoisseur of the port and of great experience, did the maneuver and, usually, did it well;
  • it was the fourth day of good weather and the current had to be less strong than when the other incidents had occurred.

I was not at all convinced, but I was not able to impose myself anyway, also because, deep down, I too thought that, if the maneuver was set well, the situation could be managed.

The confrontation, from a psychological point of view, did not end well. On the one hand there was me, the pilot, who was defending my position and on the other there was the commander who was dying to show me how good he was even in that difficult situation. In practice, a common point of view had not been reached which would have been the basis for a shared maneuver.

Under normal conditions, you reach the point of maneuver with a decent speed, stop the engines in time, put the left engine in reverse, the bow to the left and the ship rotates, almost in a skid. At the right moment the starboard engine is also put back and the game is done.

This time, thanks to the psychological defect of our confrontation, to demonstrate his skill we reached the bottom of the canal with an even faster speed than usual; and the more I told him that with that current we were going too fast, the more he would send me messages with his eyes 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 closed to the flow of the current, the situation worsened.

The ship began to drop quickly on its stomach.

In the moment of hesitation of the commander, I intervened, suggesting to put the engines in reverse and the bow thruster to the left. The purpose was to hit whilst the vessel was stationary, to avoid causing openings in the hull. We hit three times, recovering space on each rebound. We managed the engines to remain as gentle as possible and always 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 myself, and in that of the commander, for the consequences of his presumption, left their mark on us for a long time.

Ph: J.Gatti

But let’s go back to the wind.

Also in this case, experience has an important weight. 

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

Experience leads to an unconscious and automatic analysis of numerous variables which results in awareness of the precautions necessary for carrying out a maneuver.

Obviously, an absolutely satisfactory safety margin must be maintained.

Where this margin is effected or when experience is not sufficient, it becomes necessary to support the feelings with mathematics. There are many practical formulas that come to our aid to establish the force of the wind in tons.

There are some that offer the possibility of calculating this force based on the angle of incidence of the wind, others that also take into account the density of the air, here I propose a simple formula that still offers reliable results:

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

Consider, for example, a 366 meter long container carrier, with an 11 meter freeboard, loaded with five rows of containers along its entire length. How strong will the wind be, in tons, blowing across it with 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

Strength of v. a 25 kn = (12.5 × 12.5) x (8418): 18 = 73 Ton approx

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

I stop here, aware that the topic deserves to be studied much more. 

However, it is in our plans to dedicate an entire video (and an eBook) to the wind and its secrets.

Ph: J.Gatti

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