Fear, not the elements, is the biggest hurdle when the moment comes to face the Southern Ocean. That is the surprising advice Sir Chay Blyth will be giving the 216 crews of the Global Challenge race this week before they head out from Buenos Aires on Sunday for the 6,100 -mile leg to Wellington, New Zealand. He will spell out bluntly what lies ahead, but also tell them that they have the expertise it takes, furnishing them with one of his favourite mottos: knowledge dispels fear.

“People are worried about it,” he admits. “Although they’ve now sailed 6,000 miles on top of their training, they’re apprehensive about Cape Horn. They’ll be sort of protected by the landmass as they go down there, but at Cape Horn they’ll face the full force of the Southern Ocean and the short, sharp seas there.”

Sir Chay knows full well that Cape Horn is much more than merely a symbolic gateway to the south. If the fleet is unlucky enough to meet a deep low at this point, it is potentially the roughest part of the voyage. In 1984 when sailing the trimaran Beefeater II he and Eric Blunn reached the tip of South America just as a storm rolled through and the fierce, piled-up seas capsized the boat. They spent 19 hours in the water before being rescued. “Those were the worst seas I’d ever seen,” he says, “and I’ve been in three hurricanes.

“I would describe them as legions coming towards you one after the other, long lines of waves that march up, crash down and build up again. It is true that there are these odd waves that seem to be slightly different from the rest. Fortunately, when you’ve been at sea a long time you get a feel when they come hissing towards you for when they’re going to hit you badly and when they’re going to pass under the boat.”

He says that the experience of meeting the big seas of the Southern Ocean is an experience the crews must – and will – quickly adjust to. The whole routine of running the boat will change radically from what they’ve known to date, with skippers reducing crew on deck to a few at a time, and selecting drivers from their best and most focussed helmsmen.

“You come down a wave, get down to the bottom and start rising up the next wave coming in, and when you get to these odd waves that seem to be different from the rest, you’ve got to punch your way through them,” he explains. “You free off a fraction to help your speed through. What you don’t want to do is stall the boat. But that’s when you’re left in mid-air, maybe 10ft or 12ft for 40 tonnes of boat to drop down with an enormous crash. The first time it happens to you it bloody freaks you out, I tell you. You can’t believe the boat could take such punishment.”

The Southern Ocean guarantees a share of storms, as three previous Challenge races have proven, but every so often – as in 1996 – there’s a much more virulent season. “And this could be it,” says Sir Chay. “They’re saying down here [in Buenos Aires] the weather is very different than normal, and they’ve had very heavy duty winds.”

He agrees that more detailed and sophisticated weather information is benefiting the fleet, but makes the point that, unlike on downwind races, when you are going to windward in the Southern Ocean, there’s not too much you can do with that knowledge. “When it’s coming in fast you can’t get out of its way. But it does give you some warning.”

Once round Cape Horn, safety is “the paramount thing”, something that is repeatedly drilled into skippers and crew. Yet no matter how hard it gets, Sir Chay anticipates that crews will keep racing.

“They’re pushing the boats hard. These guys are out to win,” he says. “The biggest worry is people getting bashed around. They’re driving into these seas instead of backing off while they change headsails. But you’ve got to keep on going forward and every little bit helps.”