Sailing below the coast: how the wind behaves (episode 2).Islands, estuaries and capes

Cruising under the coast: what happens to sea and wind when they encounter capes, islands, low coasts or high cliffs?
Second installment(first here) of our short practical handbook on the basic elements of meteorology for coastal cruising.
Some tips (and even a bit of “philosophy”) to make summer cruising more fun and safer.

Peaks and heads, where the landscape is transformed

The wind when it encounters a promontory naturally tends to go around it, first strengthening, then fanning out as it moves away.
Obviously, the higher and steeper the headland, the more sensitive the effect.
For every sailor, whether more or less experienced, the “cape,” headlands also represent important destinations from a symbolic point of view.
Points to be reached and overcome, they delineate the transition from one landscape to another.
They are also often the place to redoss, to give bottom in calm waters after facing challenging weather conditions. In our seas we have spectacular cases such as Cap Corse, which often represents the point after which one can shelter from the Mistral, but at the same time where its acceleration and the presence of a long Fetch (a marine stretch along which waves can run undisturbed assuming maximum values of height, length, period and speed) coming from the French coast, can turn it into one of the most insidious places in the Mediterranean. Even more significant are the straits, where you pass between two capes, and there the Venturi effect is at its best.
Personally, the most “impressive” cape I have passed is that of Tarifa where, once you pass Gibraltar, you leave the Mare Nostrum behind and enter the Ocean.
I passed it on a day with dark skies and a tense wind in favor and an adverse current (she also has a very similar behavior to the wind, always much more powerful at the tip of the cape): the result was a swarming and crazy sea that I had never seen.
In addition, a small school of giant garfish had decided to snatch a passage by lining up perfectly behind our stern as we were barely sailing at 3/4.knots.
In short, a spectacular welcome just outside our “puddle.”
Similarly, there are heads and straits that because of their unexaggerated size we tend to take for easy, but that hide quite a few pitfalls, such as the Piombino channel (always underestimated but capable of changing faces in an instant) and the Strait of Messina.
Here, too, the collision of wind and currents in opposite directions complicates the lives of co-moders of even large commercial vessels in no small measure (but conversely makes fishermen happy).
The examples can be almost endless, but surely the Straits of Bonifacio, between Corsica and Sardinia, deserve a mention.
Here the Venturi effect finds its spectacular staging when the Mistral from the Valle de Rodano arrives undisturbed as far as the only possible passage between the two large islands, a place full of shoals and pitfalls but also, fortunately, full of wonderful sheltering in which to take refuge while outside the Mistral dictates its law.

Sailing under the coast: estuaries, a world on the move

The effect
Venturi (”
The pressure of a fluid current increases as its velocity decreases , and vice versa,” in short, for what concerns us most closely for this article: the velocity of a fluid’s flow increases when it is forced through a bottleneck)is very evident at the entrance to river estuaries where the wind is channeled by the “funnel-like” relief of the banks.
At the point where fresh water meets salt water (and even more so where ocean water meets salt water) the large indentations carved out by rivers before they flow into the sea are, more than any other part of the coast, complex places to navigate.
There is not only the effect of the main river to consider, but also that of the many smaller waterways that flow into the same delta.
There are dozens of examples in the Mediterranean, but even more numerous, and one must always deal with them, in Northern Europe and along the English Channel, where tides reach ranges unthinkable for us.
Each time, this complex meeting of different fluids represents a special case, shaped by the character and flow of the river, the power of the sea, and the importance of the tides.
The wind is often channeled and then diverted in the direction of the riverbed. The steeper the banks, the more sensitive this phenomenon will be.
The Venturi effect is usually felt more in the stretch further downstream.
Further upstream, as you move inland, the wind is more disturbed by vegetation, becomes less regular and often weaker.
Currents are subject to the same Venturi effect: the narrower the riverbed, the stronger the ebb and flow.
Unlike wind, current invariably follows the riverbed, following the meanders of ebb and flood.
The real danger is often the “bar” with associated shallows that form at the entrance to estuaries and can form rapidly especially when wind and current act in opposite directions.

leggi anche

There is still time (until July 15) to apply for the 2025 ecobonus and get the electric motor!

Islands, where every sailor wants to go

We left them for last, obviously not for reasons of importance, quite the contrary.
In their small (or sometimes large) way, they represent the sum total of what we have said above.
They are an independent ecosystem, where one can find all the effects we have described in talking about high and low coasts, estuaries, capes, headlands, and even channels.
They often represent the racer’s “paradise,” and particularly the tactician’s; deciding to pass on the right side can be the ultimate choice to clinch a victory.
As we said in the beginning, however, in this article we are addressing those who primarily go to sea for cruising.
And here the advice is: adopt an island, it will become your training ground for understanding the world (the navigable one).
We certainly have no shortage of them, from West to East the Mediterranean is full of them.
We all have our archipelagos of choice, to which we return periodically: Cyclades?
Southern Croatia?
Balearics?
Magdalena?
Dodecanese?
Certainly by studying their characteristics, year after year much can be learned.
Personally, I understood the beauty of sailing (and of finding a safe shelter) when I discovered Cala Lazzarina, on Lavezzi. One sleeps on three meters of sandy seabed and even when the Mistral roars outside, sheltered by what looks like just a simple strip of rocks, in absolute tranquility.
In the place of so many famous shipwrecks one feels sheltered, safe.
At peace with the seascape.
The same goes for the Cyclades, in summer, when the Meltemi blows hard without ever letting up day or night.
I LOVE getting to Anafi, dodging heads where the wind picks up even more, reaching “my” roadstead giving bottom and putting tops ashore.
Protecting me is a steep cliff, the Meltemi occasionally sticks a little “bastard” to the side, the boat wields a lot.
But I know I’m safe.
Photo: courtesy Jeanneau