The road to Rio

James Boyd previews leg four of the Volvo Ocean Race

Leg four of the Volvo Ocean Race kicks off on Sunday, taking the boats back into the depths of the Southern Ocean. For crews this is the leg that it is all about - hard running and reaching in strong breeze and some of the world's largest waves - and in years to come they will recount to their grandchild their rounding of the treacherous Cape Horn.

At 1300 local time on Sunday (midnight Saturday if you're on GMT), this 6,700 leg will set off from Auckland. Traditionally the Auckland start is one of the highlights of this race with local Aucklanders turning out in force to see the boats off. It was here 12 years ago that the rigging of an anchored spectator yacht snagged the mizzen on Roger Nilson's maxi ketch The Card ripping it off.

As there was at the start of leg two there will be some tactics involved as the boats dive south to get back into the strong westerlines of the Southern Ocean, the choices varying between a more southerly route (as News Corp took leaving Cape Town) to get into the westerlies first, or a south easterly route that is closer to the great circle. It is very likely that one of the boats in the mid to low end of the fleet - djuice or SEB in particular - will pull a flier at this stage.

For navigators the aim for the Southern Ocean portion of this leg is to get south to Cape Horn at 57degS on the shortest possible course in favourable winds. The toss up is that the great circle takes the boats down to 64degS, or starting further north where the conditions are more favourable. At 64degS the boats would experience icebergs, snow and ice on the deck and this would be extremely debilitating for the crew, but more importantly, although the depressions in the Pacific part of the Southern Ocean track further south than they do in the Indian Ocean part - they don't go that far south!

In many races in this area navigators look at the average weather conditions prior to the start and pre-plan a line of latitude they will sail down to take them across to Cape Horn once they have arrived in the Southern Ocean. This line of latitude is unlikely to be at more than 60degS, which will mean greater distance to sail, but a faster ride.

The classic Southern Ocean sailing conditions take place on this part of the race because the depressions which track around the Southern Ocean are usually much larger here than they are in the Indian Ocean. As a result of this the swell is more developed and regular, and the boats experience less confused seas than on leg two. So, surfing down big, big swells is the order of the day. It was in these waters four years ago that the crew that Lawrie Smith's crew became a little too enthusiastic and saw their rig disappear over the side. This time the crews will no doubt show even more enthusiasm in the knowledge that their new carbon fibre masts, introduced for this race, will take a lot more abuse before they snap. There is every possibility that we will see the monohull 24 hour record tumble before Cape Town.

Cape Horn may deliver some horrible conditions in which case it is a very bad place to be. The winds funnel between the Antarctic Peninsula to the south and the South American continent to the north and the sea floor shelves steeply creating a short, sharp sea. Although meteo statistics show this to be a fearsome place, and indeed three races ago the maxi NCB Ireland reported gusts of 70 knots here, a vast majority of times it is benign when races go round. Most round the world race schedules are established so they round Cape Horn when it is potentially at its most peaceful.

Once round the Horn the boats head up the south Atlantic and again the navigators are in the hot seat. They want to stick with the northerly flowing current and avoid the southerly flowing Brazil current and must play the calms and gales caused by the interrupted flow of wind across the South American continent. It was here four years ago that the Dutch yacht Brunel Sunergy pulled off an incredible flier. Seeing the boats ahead of her parked up, she bore off to the east and even left the Falklands to port. She sailed around the fleet and finished this leg in second place.

The trip up the Brazilian coast is usually a fairly unpleasant ride for the boats as they must endure a beat into the Trades. This is confounded on the home straight into Rio de Janiero which is often a windless zone.