The Mediterranean is one of the most popular destinations for sailors to take their boat out and battle the elements, or to compete with other sailors in one of the many regattas. Whether you are a leisure or competitive sailor, you should have a basic understanding of everything that affects your sailing. This means being able to read the clouds and predict the weather from them, knowing what type of winds are in the region at different times, and understanding the ocean currents and how they affect sailing. These currents can be a hindrance as well as a welcome boost. Read on to find out how to use them to your advantage.
What are ocean currents: the sea never sleeps
An ocean current is essentially a large body of seawater continually moving due to a variety of forces acting on it. It is a constant cycle of vertical and horizontal movement by water masses in the oceans and seas. Winds on the sea's surface, differing pressures in the water at different depths, and tidal forces from the moon and sun all contribute to the formation of ocean currents. Their direction is then determined by the rotation of the earth and the periodic winds.
Illustrative world map of ocean currents
Ocean currents can then be defined as the results of a horizontal and vertical system. The horizontal system consists of surface and deep-sea water circulation. Thevertical system is determined by the upward and downward currents of the seawater mass. Other factors influencing the formation of ocean currents include the different salinity of the water in differentdifferent salinities at different depths, temperature differences or the levelling of the sea level between the seas and the oceans. All these parameters also determine, among other things, the strength of the current and the height of the tide. Just to give you an idea, the speed of currents in the Mediterranean in the open sea is about 0.5 to 1 km/h, but in the straits, which act like a jet of wind, it can increase to 2 to 4 km/h. The Gulf Stream moves at 6 to 10 km/h.
The Mediterranean: what countries it covers
The Mediterranean Sea could be considered a very large lake, as it is surrounded on all sides by land and connected to the Atlantic Ocean only by the narrow Strait of Gibraltar. If we list all the countries alphabetically, the Mediterranean Sea bathes the shores of Albania, Algeria, Bosnia and Herzegovina, Croatia, Egypt, France, Greece, Italy, Israel, Lebanon, Libya, Malta (island state), Monaco, Montenegro, Morocco, Slovenia, Spain, Syria and Turkey. It's no surprise that the Mediterranean Sea is also known as the bridge between the three continents and, with an area of approximately 2,500 km² , it spans Africa, Asia and Europe.
Each coastline has its own specifics. The varied terrain affects the regular winds, which in turn affect the currents as do the depth and temperature of the sea, its salinity and the relief of the seabed. The four largest peninsulas in the Mediterranean also influence the sea currents : Apennine, Balkan, Iberian and Asia Minor, and large islands such as Sicily, Corsica, Sardinia, Crete, Malta and Rhodes. The Mediterranean Sea is then divided into smaller units — between the French Riviera and Corsica is the Ligurian Sea; the Adriatic Sea is bounded by the shores of Albania, Bosnia and Herzegovina, Croatia, Italy, Montenegro, and Slovenia; between Greece and southern Italy is the Ionian Sea; the Cretan Sea bathes the shores of Crete and peninsular Greece; and the body of water between Turkey and Greece is called the Aegean Sea.
Currents in the Mediterranean are not powerful
In the Mediterranean, you don't usually encounter powerful currents and many are weak to negligible. This is mainly due to the continental location and climate. Since the Mediterranean has hot or mild weather for much of the year, the water tends to evaporate. The lowering of the water level then leads to the inflow of water in the upper layers from the Atlantic Ocean and the Black Sea. Conversely, at greater depths, where the water is saltier, the process works in reverse — salt water flows into the Atlantic Ocean and Black Sea. Currents can therefore flow from the Atlantic and Black Sea to the Mediterranean or vice versa.
You can easily tell by the temperature of the sea. In general, the sea is colder and fresher in the west and warms towards the east. When it is hotter and the water evaporates, you can expect a surface current towards the Mediterranean and vice versa. The currents in the Mediterranean thus follow this inflow and outflow, are directed by the coasts of the mainland and islands, and are most influenced by the winds typical of the Mediterranean. The straits between islands or between islands and the mainland can also, as in the case of winds, act as a nozzle and strengthen the current considerably.
YACHTING.COM TIP: Are you curious about the winds that occur regularly in the Mediterranean, influencing the strength and direction of the currents in the area? Read our detailed guide to the 7 most common winds you'll encounter in the Mediterranean.
Tidal phenomena in the Mediterranean
The tides are not very strong in the Mediterranean, although of course, it all depends on the time of year and the specific wind that is blowing. Under usual conditions, sea level changes by centimetres at low tide and by a maximum of about one metre at high tide. There are, of course, exceptions, where the tide, together with the swell driven inshore from the sea, can raise the level by as much as 4 metres (typically in northern Corsica or the Strait of Genoa). As with currents, straits and narrow channels can amplify the tide. Finally, the time of year also plays a role, with the Mediterranean being more turbulent in the winter months, with bigger waves and stronger currents.
YACHTING.COM TIP: If you like more sporty sailing, the coast between Corsica and Sardinia is ideal. The high white cliffs, enclosed coves, romantic beaches and the magical islands and islets of La Maddalena Park in the Strait of Bonifacio will transport you to a yachting paradise! Take a look at our article, Unbridled yachting in the crystal-clear sea of southern Corsica and the Strait of Bonifacio, where we also recommend the best sailing route to take.
Why it's important for sailors to monitor sea temperature
When you first think about it, it may seem that determining the temperature of water is not exactly rocket science. Either the weather is hot and sunny and the water is warm, or it is cloudy and cool and the water is cold. In reality, it's not that simple with the sea temperature affected by a variety of factors. For starters, the temperature is influenced by elements that do not fluctuate significantly over time, such as seafloor relief or depth. Then there are the variables that vary all the time. These mostly include the amount of solar radiation, currents, and pressure fluctuations at various water depths (temperature gradient). Changes in sea temperature can then tell us a lot about the currents.
Consider the following scenario — you're sailing in beautiful sunny weather, and the top half metre or so of water under the surface is being warmed by the sun's rays. However, they do not reach much further, so the water is substantially colder 10 to 20 metres deeper (five degrees Celsius or more). Such temperature differences lead to convection, a vertical upward motion that attempts to even out or reduce temperature differences. At that point, a vertical current is created.
Wind and currents have a greater impact on the change in surface seawater temperature. Winds cause waves to form at sea, which speeds up the mixing of the bottom and top layers of water, resulting in a reduction in surface temperature. Logically, then, the stronger the wind, the more intense the mixing and the colder the water. The currents mixing the water work in a similar way.
Which way do the currents in the Mediterranean flow?
In general, in the southern Mediterranean, currents typically flow from west to east, in the north they flow from east to west, and in the middle of the Mediterranean, currents move in eddies that can be hundreds of kilometres long. Therefore a sailor has three variables (solar radiation, wind and currents) that determine sea temperature and from which to estimate currents.
How to prepare for sailing in ocean currents
Although the currents in the Mediterranean are not very strong, preparations for sailing in the current usually lies on the shoulders of the navigator or captain. In a given location, the strength and direction of the current is constantly changing, although they often recur periodically and behave predictably. This is good news for the navigator or skipper because they can predict currents based on detailed historical data, tables, charts or maps.
What should you do before setting sail?
Before setting sail, it is advisable to make a list of useful data, which should include information about your boat's draft, expected tide times, height, range, speed and direction. Check how the current generally behaves where your route takes you — especially in the shallows, marina entrances, headlands, estuaries, sandbanks, etc. Don't forget to include a weather forecast in your prep and have a backup plan in case of bad weather. With all of this information, you'll be able to precisely plan your departure and arrival dates to the marina, take advantage of tidal currents to reduce your travel time, and avoid the potential dangers that currents and tides can cause.
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Practical tips for sailing in ocean currents: don't rely on autopilot
Sailing in a current has unique characteristics that depend on where you are sailing, the strength of the wind is and what direction it is in relation to the current. Although the currents in the Mediterranean are usually not very powerful, it is still worth studying nautical charts before departure, which show the usual currents on your route, and check a detailed weather forecast. A basic rule of thumb is that the lighter the wind and smaller the waves, the more the current, tide or swell will affect your boat. On the water, be on the lookout for buoys, anchored boats, breaking waves or other obstacles that the current has to go around to get an idea of where it's flowing, if it's breaking, and how strong it is. The current can be both your friend and your enemy.
True wind, boat speed wind and apparent wind
The strength of the sea current relative to the wind and their direction will determine the setup and trim of the boat. The whole principle is based on the concept — true wind, riding wind and apparent wind. The true wind is the wind we measure in a stationary position on an anemometer. The induced wind (boat speed wind) is the resistance we have to the air as we move (for example, if you move 30 km/h in no wind, the induced wind will be 30 km/h). Apparent wind is a combination of both of these forces.
Apparent wind always veers more away from the bow of the boat, and the boat changes speed according to the course it is sailing. If you add in waves, where going from the top of a wave to the slope between the waves literally kicks the boat, the headwind changes and so does the apparent wind. This is important information especially for skippers who use the autopilot. It does not detect the actual wind, but only the apparent wind, and tries to change course so that the apparent wind is still blowing from the same direction. This can lead to unpleasant surprise manoeuvres, especially when you are sailing on a tailwind and the boat gybing.
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The ability to calculate apparent wind speed based on actual and induced winds will also save you a lot of trouble setting and reefing sails when sailing against or with the current. As a general rule, if the wind is coming from the same direction as the current, you can afford to flatten the sails because you are being driven by both the wind and the current. If the current is flowing in the opposite direction to the wind, it pays to keep the sails slacker or furl them at the top spars to give you more acceleration.