Ph: F.Parisi

The Wind

SBEBy SBE10 May 202211 Minutes

The wind

Every port presents its difficulties.

Some can be fog that creates complications; with others, it’s the wind, the current, confined spaces or exceptionally shallow water.

Combining several of these elements can present more significant risks for ship handling.

Today we are going to talk about the wind.

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

I said, “the wind can help sometimes”: I am referring, for example, to those situations in which a light wind can help push a vessel away from the quay during unmooring; or, similarly, when a light breeze gently accompanies us to the berth. The wind blowing from the correct direction and a length of chain on the bottom can allow us to turn a ship on the spot without the aid of the engine or thrusters; again, a well-calculated wind force concerning the windage can facilitate a favourable approach or departure.

Another aspect not often considered, which is also interesting, is that the wind often helps the pilot in the ship handling “pre-organization”. In fact, in the briefing phase with the ship’s captain, one of the most delicate aspects regards the eventual number of tugs to be used during the manoeuvre. The dangers posed by wind and current are similar, but the wind is perceptible and visible, whilst optimal weather conditions can also accompany the more subtle current. It’s much easier to convince the captain when he can hear the wind whistling and see the sea streaked with ‘white caps’ to discuss an invisible danger lurking beneath the sea’s surface.

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

Four days of solid sirocco accompanied by overcast skies and rain showers are the setting for 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 from the East and vented to the West was particularly violent. It was a strong current, but for the first two days at least, it was still predictable. This wild and invisible force represented the anomaly. It continued vigorously under the sea’s surface on the third and fourth days, even though the weather continued to be ideal. 

Hence, it was challenging to convince captains of the importance of 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 specific situation a little 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 case. Besides, we, too, expected the usual downsizing of the current in a short time.

In short, three ships, during the 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 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 regularly calls 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 day’s incidents and the abnormal presence of this strong current. A condescending look was the conceivable reaction. I tried to insist, but the reasoning that he used had solid foundations: 

  • the ship manoeuvred skillfully;
  • 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 must have been less intense than the days on which the other incidents occurred.

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

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, we would reach the point of manoeuvre at a decent speed, stop the engines, decisively reverse the port engine, bow thruster to the port, and the ship would rotate, almost drifting. Reverse the starboard engine at the right moment to do the job.

The captain arrives at the channel’s end at an even faster speed than usual to demonstrate his skill. The more I told him that we were going too fast with that current, the more he would send me messages with his eyes, looking 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 reversing the engines and putting the bow thruster to port. The aim was to collide whilst the vessel was stationary to avoid causing hull breaches; we crashed three times, recovering space behind on each rebound. We managed the engines to touch as gently as possible and always when stationary. Finally, we managed to get out of the current and reach the mooring position. 

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 a critical part to play in this case too.

The differences between ships are not limited to classification by type or size. The same vessel has different characteristics depending on its draft or load on deck. Under the same conditions, unexpected obstacles or differing weather and sea conditions can influence the same manoeuvre with the same ship.

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

We must maintain an acceptable 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 aid us in establishing wind force in tons.

Some offer the possibility of calculating this force using the angle of incidence of the wind; 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 stop here, aware that this topic deserves to be explored.

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