The leaders of the Vendée Globe have only been sailing in the Southern Ocean for a week and the Roaring Forties have already claimed numerous victims. This is certainly not an easy area to sail, and it is far from over. As we will see, the leading group is in for another violent storm over the next few days.
But first let's take a look back - and at a worrying accumulation of breakdowns in several respects. Three top skippers have been hit in the past few days. Two of them - Samantha Davies on "Initiatives Cœur" and Sébastien Simon on "Arkéa Paprec" - were knocked out of the race by collisions with unidentified floating objects. Kevin Escoffier even lost his boat when he nosedived down a steep wave at breakneck speed and the hull of his "PRB" literally shattered.
It may seem like a coincidence that all the incidents took place around the same time and in the same sea area. But there is some evidence to suggest that it had to do with the peculiarities of the region in which they were sailing: almost exactly south of the Cape of Good Hope.
There is a powerful ocean current there, the notorious Agulhas Current, which originates in the Indian Ocean and moves southwards along the east coast of Africa.
Where it separates from the continent, it meets the eastward-flowing currents of the Southern Ocean caused by the wind at around 40 degrees south latitude. In this zone, smaller eddies of warm water split off from the Agulhas Current.
There are two things to note here: Firstly, the Agulhas Current carries flotsam with it, which it collects along the East African coast. The objects are carried along in the surface water up to the aforementioned convergence zone at 40 degrees south latitude - exactly where Sam Davies and Seb Simon were sailing when they had their collisions.
Secondly, the south-westerly Agulhas current acts against the prevailing wind and wave directions, pulling eastwards. These opposing forces lead to a very irregular, split swell, and they can also increase the wave height.
The region is notorious for monster seas - known in English as "freak waves", which are at least twice as high as the average wave height. We are waiting to learn more about what exactly happened to Kevin Escoffier's PRB; it is quite likely that conditions like these contributed to his sudden wreck.
Looking at the weather over the coming days, there is an interesting point about strategy - and that is how comparatively slow the top placed skippers are sailing.
In fact, the conditions seem to be too tough for foiling. It is becoming increasingly clear that many sailors are deliberately slowing down in order to maintain their boats. We have rarely seen average speeds above 20 knots. Both the accelerations and the decelerations in the waves are much greater - the speed often oscillates between 10 and over 30 knots. Some of the conventional boats without hydrofoils, which accelerate less extremely, have therefore managed to make up many miles on the front runners, such as Benjamin Dutreux and Damien Seguin.
The skippers of the foiling Imocas will have to take this into account when determining their strategies for the fifth week of the Vendée Globe. They are currently only sailing at around 80 per cent of optimum speed, which will have an impact on their position and future route choices - in particular whether or not they manage to stick to a weather system.
A strong area of low pressure is currently approaching the fleet. It is moving from the south in a north-easterly direction across the peak area. It is already a very large and powerful system and over the next few days we will see it strengthen along the associated cold front. A secondary low is also developing along this cold front, which is crossing the course of the fleet. An explosive situation.
The reason for this is warm air that is directed southwards by a high in the north. Where it meets the polar air of the low, a very active cold front develops with strong winds and storms.
Over the next 36 hours, the skippers will have to assess and decide how long they can or want to sail ahead of the cold front before it overtakes them. The north-westerly wind direction that prevails in front of the front allows a direct easterly route - and therefore the chance to break away. However, this strategy also requires caution - because a strengthening cold front can lead to extremely difficult conditions in the Southern Ocean. A more cautious course could ultimately prove to be faster, and certainly less risky.
Boats like "Apivia" and "LinkedOut" can theoretically stay ahead of the front until Wednesday, while the Imocas a little further behind, such as Boris Herrmann's "Seaexplorer", will probably stay astern tomorrow morning. It will be a really difficult balance to strike - especially as only a third of the lap around the world has been completed and there are still around 50 days of this race to go.
Once this front has passed through, the wind will shift abruptly to the south-east and die down to a reasonable 20 to 25 knots. Such wind speeds are actually much better for sailing faster, so being dropped might not be the worst thing. However, the wind angle is not the best fit - it gets a bit too deep for the direct course. As the low pulls away to the east, the high in the north-west becomes weather-dominant. This means that the wind will slowly shift from west to south-west.
Next Saturday, the leaders will probably already be at the height of Western Australia. A difficult transition may develop here between the high in the west and a high near Tasmania. In between lies a zone with weak winds. This may be an opportunity for the following skippers to make up a few miles as the fleet shifts together. Current route calculations see Boris Herrmann only 250 nautical miles behind Charlie Dalin at the end of next week. But first he will have to master a few days of difficult conditions in the southern ocean.
