Once a week, the experienced ocean-going professional and navigator Will Harris analyzes exclusively for YACHT online which challenges await the Imoca skippers. Today: About the baptism of fire at the start of the Vendée Globe, about the high-speed chase that has just begun in the Passat, and what surprises the horse widths near the equator have in store:
"Seven days have passed since the start of the Vendée Globe and it has been difficult to keep up with the amount of news and events. Two top runners and favorites, 'Charal' and 'L'Occitane', are already out of the running for Both suffered damage to their boats during the strong cold front that struck the fleet last Wednesday.
The complicated weather conditions have meant that the modern foilers have not yet been able to play their ace to the full. With every storm system in the North Atlantic, a short steep sea has developed which has made it very difficult to let the boats 'fly'.
The slower constructions with plug-in swords, which had taken a more direct south route away from the cold front at Cap Finisterre, were actually able to fight for the lead - even if only temporarily. This more southerly route seemed too light wind in the forecasts, but at the moment Jean Le Cam, who has led this southern group from the beginning, is in 2nd place overall, only 30 nautical miles behind Alex Thomson's 'Hugo Boss'.
After all, the fleet had to deal with the subtropical storm Thet for the past 48 hours. This crossed directly the way of the fleet on their route south, and when the skippers developed their strategies before and shortly after the start, they probably had not expected that it would develop into a record-breaking storm.
We saw some co-favorite skippers like Charlie Dalin on 'Apivia' and Thomas Ruyant on 'LinkedOut' who decided to sail around the storm and consciously took a longer and slower route to avoid the worst. Alex Thomson, on the other hand, who is currently at the helm, did not throttle and sailed within 70 miles to the core of Theta, where he reported winds of up to 60 knots at times. This risk, which according to his team gave him a hairy throat, seems to have paid off.
The fleet will be grateful to have finally achieved steady weather. The trade winds are a typical wind regime that is influenced by the Azores high. They lie south of the anticyclone and their strength, direction and position are determined by the position of that high.
Typically, the Passat in the northern hemisphere blows from the northeast with an average of 15 to 20 knots - it allows a fantastic and fast reach to the equator. Between 7 degrees north and 20 degrees north (the fleet is currently at 23 degrees north) the trade winds are fairly constant. Above 20 North there is more influence from other weather systems. When storm Thet broke through, the trade winds over 20 north completely subsided, which is why the skippers moved west last week. Even today, the trades are weakened by thets, but the low quickly loses its power and influence.
Figure 1: The weather route to the southern hemisphere for Boris Herrmann on "Seaexplorer". He is expected to arrive at the entrance to the Kalmen on Wednesday morning. Until then, it's a straightforward drag race and a test of who has the fastest boat. The general rule for crossing the slack is never to be further east of 25 degrees west as the light wind zone becomes wider there
Now most of the fleet sails in these steady trade winds and can sail a direct route south and to the Doldrums at about 7 degrees north, which they are expected to reach on Wednesday. These are ideal conditions for the Imocas with foils. Fairly flat water and aft wind make you expect impressive speeds, especially of the latest generation.
In the next few days it will be a pure speed race. Who has done the most tests and optimized their boat for these conditions? It only takes a speed advantage of 5 to 10 percent to be able to break away quickly. A lead of 100 miles, as Alex Thompson has on "Hugo Boss", can easily double - or disappear - within 24 hours. So keep an eye on the tracker. It will be revealing!
The other thing to consider is the passage of the Kalmen Belt. For this, the skippers have to position themselves relatively early. The Kalms or 'Doldrums' are a light wind band that focuses on the Inter Tropical Convergence Zone (ITCZ).
It is the convergence of the trade winds from the northern and southern hemispheres. Low pressure is created by convective activity, which causes air to rise. In the process, large cumulonimbus clouds form, which cause light and irregular winds on the sea surface. This zone is complicated to navigate and requires constant attention in order to choose the best route through it.
At this time of year the Doldrums are between 7 and 4 degrees north, so that this band is about 200 nautical miles wide. They are also wider off the West African coast, so we normally won't see anyone sailing east of 25 degrees west.
Typically the fleet will compress as it approaches the Kalms. The front runners sail into the lighter winds first, so that the boats behind can catch up. But the boats that are the first to leave the infamous area and reach the trade winds of the southern hemisphere first will regain their leadership just as quickly.
Figure 2: The typical characteristics of the Doldrums according to the weather forecast. The general picture is correct, but the details can vary significantly. In the east the "African triangle" with very light winds, which should be avoided at all costs
Due to the complexity of the doldrums, it is extremely difficult to provide a weather forecast for the participants. Forecasts in this area are generally quite unreliable. Instead, the skippers must use satellite imagery and look at the winds in the upper layers to determine the best place to cross the region. Just a few hundred meters east-west positioning can make a big difference. Hitting the wrong side of a cloud can leave you stuck in a wind hole for hours.
Figure 3: An infrared satellite image of the intertropical convergence zone. The brightly colored areas indicate a lot of activity and usually there are irregular and unstable winds here
If you look at the forecast now, the Doldrums seem to be in a relatively stable phase. The light wind triangle that extends westward from the African coast is quite small, and the ITCZ is oriented directly east-west; it does not meander north or south. However, this situation can change completely in less than a day.
The next few days will undoubtedly be fascinating. Who will make it through the doldrums first? In the course of Vendée's history, the boat that can do this usually has a very good chance of winning the race as a whole. Because once the Imoca skippers sail in the southern hemisphere, the fleet is divided into different weather systems. Then the opportunities to overtake become less frequent. So it is possible that Alex Thomson could have already made a kind of preliminary decision through his willingness to take risks when passing Thet - at least if he masters the horse widths with similar fortune and determination.