Vendée Globe

Consider an island with a surface area of not much more than 120 Km2 sitting almost 2000 kilometres off the coast of Africa and 3500 from Brazil. It made the ideal site for an open-air prison: the English realised its potential when they exiled Emperor Napoleon there, before sending Boer prisoners there during the war of the same name at the end of the nineteenth Century.

With just 5000 inhabitants, no proper resources of its own, no harbour, the island does not really much charm, apart from for those, who are nostalgic for the First Empire, who visit the tomb of their hero in Longwood.
St. Helena is a place that sailors are required to pay ttention to: as the island gave its name to the famous high-pressure area, which is the South Atlantic equivalent of the Azores High to be found in the northern temperate region.
 
The shortest route

A short lesson to start: an anticyclone is an area of high pressure. At its centre, the winds are light or calm. That is a pity, as from the Doldrums to the Cape of Good Hope, the direct route goes close to the island… In normal times, this route is out of the question.  The wisest move is to head off around the western side of the high and take advantage of the winds on its edge. Here, sailors have to change their way of thinking, s now they are upside down, the basic concepts have changed. Thanks to Coriolis, we know that the Earth's rotation leads to forces pushing things to the right in the northern hemisphere and to the left in the southern hemisphere. In short, the wind turns clockwise north of the Equator around an anticyclone, and counter-clockwise in the south.  Having crossed the imaginary line, our sailors tackle the western side of the high with some upwind sailing in S to SE'ly winds, which back E'ly and NE'ly, then N and NW'ly. When you start to pick up the westerly flow, you can assume that the worst is over.
The goal is therefore to find a compromise between taking a short cut and sticking with the wind to ensure you do not get slowed up
 
St. Helena's little joke

Although the St. Helena high is usually more stable than the Azores high in the north, it can be subject to some minor interruptions.  A rainy front moving in from Argentina creates a low-pressure trough dividing the high in two.  The two halves are not the same and their behaviour  is very difficult to predict. Occasionally, St Helena can block the way south via the western face allowing a more direct route. The temptation is therefore to move to the left and try to find a way through: but this is a high risk strategy. But in 1991, Isabelle Autissier pulled off a master stroke in the BOC Challenge leaving those chasing after her several hundred miles behind.  To a lesser extent in the last Vendée Globe, the duo of Riou – Le Cam managed to slip through a gap and build up a large lead over the rest of the fleet.  This strategy requires a lot of inspiration, some daring and probably a lot of luck.  As the Vendée Globe competitors tackle this stretch of the course, the high appears to be toying with them.  The presence of a small low is upsetting the pattern and it is not clear how this will resolve itself.  At the front of the fleet, questions are being asked, while those coming along behind are probably hoping that this is an opportunity to show their skills by taking a rather unusual route.  However, we must remember that St. Helena is a very cunning old lady and more than one following in the footsteps of the Emperor has fallen into the melancholy of her huge ocean calms.

PF Bonneau

Infos précédentes :