6,700 miles, leg four of the Volvo Ocean Race from Auckland to Rio de Janeiro is a race of two halves. First it visits the icy wastes of the Southern Ocean, then once round the notorious Cape Horn, the South Atlantic section ends in the tropics.
During the 23 or so days the boats will be at sea, they can expect to encounter all manner of weather conditions from the fog and ice of the Southern Ocean, to the heat and humidity of the South Atlantic trade winds.
Once clear of New Zealand the yachts are expected to head quickly south and back into the Southern Ocean. If they follow the short route to Cape Horn at 57°S via the great circle, they will dip down to 64°S before their course levels off to the east. Sailing the shortest route will be appealing, but taking the boats this far south will make life on board tough for the crews. Heading south of 60° south conditions are freezing and there is the added risk of getting south of depressions and into head winds.
They are also likely to encounter icebergs, although if there had been a heavy concentration of bergs this year the race committee could have limited the route by imposing waypoints in the course. It is still possible they may do this prior to the start on Sunday.
In the back of each crew's mind will be the knowledge that they are sailing in the remotest ocean on earth. Half way between Auckland and the Horn they will be over 2,000 miles from land (excluding Antarctica) and any assistance, should there be an accident. In the race four years ago two boats, Silk Cut and EF Education, were dismasted in these waters.
There are 4,500 miles of Southern Ocean sailing to Cape Horn bringing strong winds and extreme sailing conditions, similar to those experienced on leg two. However the South Pacific Ocean differs from the Indian Ocean in a number of ways. Generally the depressions cover a larger area than those in the Indian Ocean bringing bigger waves but these should have a longer wavelength and be less confused.
The depressions here usually track further south allowing the yachts to also sail further south and still remain on the northern side of them, in the favourable winds. The navigators have to watch the development of these depressions carefully, particularly secondary lows, as getting caught on the south side of them would bring headwinds and punishing conditions for the crews and the boats. This is likely to dictate how far south towards the great circle route the boats will go. Close to the centres can result in light winds particularly if a depression has a number of secondary lows developing along a cold front.
Worldwide satellite measurement of waves has put the approaches to Cape Horn as having the biggest average waves on the planet. The yearly average is over 5m (16ft) and this is made worse near Diego Ramirez on the approach to Cape Horn where the water shallows from over 4000 metres deep to less than 200 metres in 15 miles. This causes the water to pile up giving steep breaking waves and can make the last few miles through the Southern Ocean very rough.
The approach to Cape Horn is like a funnel with the high mountains of South America pushing south, and the Antarctic Peninsula reaching north. Weather systems are concentrated and push through this gap accelerating the winds and giving Cape Horn its fearsome reputation. The incidence of northerly winds increases and the old pilot books warn of the danger of approaching from too far south and the difficulty vessels may have getting north again.
Even in the Southern Ocean summer winds above a force seven can be expected for over 30 percent of the time, although often Cape Horn can be benign and in the past many crews have reported making rounding as almost an anticlimax. However, one of my overriding memories when sailing past Cape Horn in the 1990 race was of hurricane force winds arriving unannounced and destroying the mainsail before it could be dropped. What followed was a very wet and exciting ride in huge breaking waves dragged along by a small blast reacher (a heavy reaching sail).
The race is timed to pass Cape Horn at the end of the summer, giving the best chance for reasonable conditions. Once around however there are still 1,000 miles to sail before the boats reach warmer waters.
Immediately after Cape Horn there are 100 miles to the Straits de la Maire, a narrow passage between Tierra del Fuego and Isla de los Estados. The tide can rip through here at 8 knots making for tricky navigation. As the wind hits the mountains they can create a huge wind shadow and even curl the wind back on itself, giving easterly winds where westerlies are expected.
The following 1,000 miles are sailed predominantly under the influence of the low-pressure systems girdling the globe to the south - usually, but not always. Four years ago as the majority of the fleet lay becalmed to the west of the Falkland Islands, Brunel Sunergy headed east and kept the wind, sailing from sixth to second place in the process.
The Southern Ocean current sends a plume of cold water to the north almost as far as the River Plate, where it meets the warm waters of the southerly flowing Brazil Current. At the confluence the currents turn to the east to mingle in the waters of the South Atlantic. The currents usually follow the 200 metre depth contour and can be monitored from space. These pictures can be accessed from the yachts as they are freely available on the internet.
If the wind allows, the navigators will follow the axis of the northbound current to gain the extra miles it gives them. The wind should be predominantly from the west although it could blow from any direction. To be watched for is the Pampero, a violent wind similar to the Southerly Buster of Australia, that follows a cold front off the land. Dividing the warm air from the cold, it can be accompanied by rain, hail, and thunder with the wind quickly reaching 60 knots (force 11).
As the weather becomes warmer and the push of the Falklands current decreases, the wind becomes more variable in the Horse Latitudes, where the trade winds and westerlies converge. With the South Atlantic high sitting to the east the trade winds will start to blow and the warm south flowing current will arrive at about the same time. Trade winds give fantastic sailing when they blow from behind but when beating into them they become tiring with the potential to break the boats. It was beating hard in these waters eight years ago that Chris Dickson's Tokio, at the time race leader in the Whitbread 60 class, broke her mast.
Tactically the options are to head inshore out of the current and hopefully pick up favourable wind swings as the day breeze establishes itself. This can be risky, as there is the potential to become becalmed during the night too close to land. Alternatively heading out into the Atlantic can also have its rewards with strong steady winds but from the wrong direction. Less current offshore will also help but should the high pressure move west, the most easterly boats could suffer.
The arrival at Rio de Janeiro can also create problems as the area can be beset with calms, making for a slow, frustrating finish after such a long, hard leg.
The overall positions will dictate tactics and these are likely to vary between the yachts depending on the relative positions. Although half way around the world, only one third of the points have been awarded and any of the top four are in with a realistic chance of an overall win. This group of four are therefore expected to stick closely together particularly for the first half to Cape Horn - 4,500 miles, taking about 14 days. With such a competitive fleet a bad result is going to be particularly painful. The addition of Paul Cayard to second placed Amer Sports One has raised the stakes still further. Leader Kostecki will want to keep illbruck close to Dalton and not allow boats to split them in the results.
On the experiences of the skippers, Dalton should excel in the Southern Ocean while Kostecki should have the edge on the short legs. Ironically the race has thrown that formbook out the window with the worst leg so far for Kostecki being the shortest leg, and for Dalton, with his powerful beamy boat, leg 2two through the Southern Ocean.
As usual it is the weather that will play the major role in determining the final outcome of the leg as Paul Cayard explains: "This game is all about gathering the information about the weather and making a routing plan that optimises this boat's potential to get down the track. Tactically you converge with the other opponents when you can take advantage of that, so you might gybe or tack when it suits you to take a gain on the other boats. The tactical game is based on the weather mostly, and Roger Nilson (navigator), I understand from Grant, has been doing a great job with all that, and that will continue to be his job, and my job is just to get the information from Roger and try to work with the routing programmes we have, to figure out where we should go."
It is likely that the yachts will head quickly south after rounding New Zealand's East Cape to pick up the westerlies and an early push from Dalton can be expected. Kostecki will no doubt continue to follow a course that is more conservative and not bet everything on one throw of the dice. The boats low down in the overall standings are likely to take more extreme courses that may offer high risk/big gains, as their biggest hope for glory is in gaining a leg win. For Team Tyco and SEB, having to retire from legs has left them with something to prove even if a good overall result is now unlikely. It would need a series of catastrophic failures among the leaders and an exceptional run of luck for any of the bottom group of four to win overall.
Once past Cape Horn the options for passing increase but so do the chances of being left behind. In the Southern Ocean it is essential to stay with the same weather system as your competitors, but once around the Horn the danger is losing the wind in high pressure and getting caught in adverse current.