Some say that this zone has inherited its name from the jar (from the French ‘pot au noir’ or ‘black pot’) which, in farms across Cape Verde, was used to collect all manner of detritus. Others, would have us believe that the slave traders threw sick slaves overboard in this zone so as to avoid spreading disease in the extremely confined spaces. Indeed, in the olden days, ships didn’t have the potential of modern-day yachts and had a lot of difficulties manoeuvring quickly and above all making headway against the wind. They could spend whole weeks stuck fast in this zone, to the extent that they sometimes had to get rid of the ship’s animals who were going stir crazy…

In fact, the British nicknamed the tropical regions the “Horse Latitudes” because the ships’ captains, ensnared by the zones of calm for days on end under blazing sunshine, got rid of the horses who were consuming much too much freshwater. Often, in the doldrums, scurvy began to decimate the crews. Synonymous with a lack of fresh food and vitamin C deficiency, this disease took the lives of two thirds of Vasco de Gama’s men during his voyage to the Indies in 1497-1498. For Anglo-Saxon sailors, the ‘doldrums’ (literally depression and melancholia) rhymed with extreme fatigue, because in order to get free of these prolonged calm spells, the crews had to set to with their oars and row Her Majesty’s imposing ships…

The various guises adopted by the doldrums

There are all types of doldrums: big ones, slender ones, zones that are distended, cone-shaped, pear-shaped, patchy, sprawling and ribbon-like… In short, this band of cloud, referred to by meteorologists as the Inter-Tropical Convergence Zone has the art of changing form and content. In fact, this weather phenomenon is simply the result of a confrontation between the trade winds of the northern hemisphere and the trade winds of the southern hemisphere, the former kicking out a NE’ly breeze, the latter a SE’ly breeze. In addition, the proximity of the equator increases the temperature of the water (27° to 29°C) and the air (35° to 40°C), generating substantial evaporation and hence a humidity rate bordering on 100%. And whoever tells of steam, tells of cloud… The hot air rises and the higher it is, the more it cools and the droplets are transformed into rain. And the doldrums are cloudy…

Improbable route through the doldrums…

Given that the zone of high pressure in the North and South also ‘breathe’ and cumuliform clouds are constantly moving and regenerating around the equator. The doldrums are continually metamorphosing, working one way on a particular day, and another the next. As such, it’s hard for the sailors to predict its extension and its density before plunging into it. However, some simple principles indicate that it is always narrower towards 30° West and longer to traverse around 20° West. As such, it’ll be necessary to target one’s entry into the doldrums to reconcile a vein of favourable wind and a trajectory not too far over to the West, because after the ITCZ, the SE’ly winds and hence upwind conditions, will carry the boats towards the Brazilian coast. As a result, the best ‘tunnel’ for traversing this steep meteorological relief seems to be located between 27° and 28° West.

In fact, the doldrums are more active when the trade winds are strong, and more stretched out when the water temperature is high: it reaches offshore of Guinea-Bissau, 28° to 30°C! This heat from the sea causes significant evaporation and hence the creation of cumulonimbus, which can stretch in altitude up to over 12,000 metres… Below these clouds, there is very strong turbulence and the upward currents can reach 15 to 30 m/s with strong electrical discharge; the visibility is reduced, the rain torrential and the gusts violent. There may even be cloudbursts (column of cloud extending as far as the surface of the sea, which accompany an eddy formed below a cumulonimbus), thunder and lightning and Saint Elmo’s fire (more or less continuous electrical discharge of moderate intensity). The doldrums are the zone where these tropical lows come into being and can be transformed by shifting across to the West in hurricanes… 

A hellish zone!

In the sky, the doldrums aren’t always pretty to look at, especially in the dark: lightning, thunder, rains that patter on deck like something out of Noah’s ark, a leaden horizon, significant variations in temperature in the squalls (we go from 40° to 25° in the showers), white, grey, anthracite, black and sometimes pink clouds with a green flash as the sun drops over the horizon… The winds do entirely their own thing, constantly altering strength and direction, switching from 0 to 35 knots in a matter of seconds as a squall rolls through. Even the best sailors admit to not knowing which way is North here!

The doldrums can be seen from very far off: some 100 miles (180km) away, the sailors can already see big cloud masses above the horizon… They generally position themselves between 8°N and 3°N, going from the African coast to up to 35° West at times as it contracts. However, the worst thing about the doldrums remains its unpredictability. It stretches, becomes longer, retracts or expands without warning: the sailor knows when he’s beginning to enter it, but not when he’ll escape it. It can last a matter of hours or a matter of days! For this first passage from North to South, the solo sailors will have to tackle a fairly inactive and not very wide-ranging doldrums as was observed by Thomas Coville, who rapidly negotiated the system two days ago. It will begin to make its presence felt at around 6°N with a trade wind easing to around ten knots, but it will already be astern of them from 4°N. As such the leaders are likely to spend just half a day enveloped in it… weather permitting.