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2008/02/02 - 17h18
The big switch...
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| Jules Verne Trophy |
| To the South of the island of Trinidad, Groupama 3 has been forced to make two gybes so as to avoid burying herself in the
Saint Helena High. 2,300 miles from the Cape of Good Hope this Saturday lunchtime, the navigator Yves Parlier estimated that
the giant trimaran was going to hold onto its day's lead in relation to the reference time, at the longitude of the African
tip.
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It was smack bang in the middle of the daily radio session with the giant trimaran, that the boat went perpendicular to
the normal course towards the Cape of Good Hope and everyone onshore questioned them about this `anomaly' after a trajectory
of almost perfect purity since the equator... The answer was as clear and simple as the voice of the navigator on Groupama,
who indicated that the wind was beginning to ease a little too much on the previous heading and that under mainsail and gennaker
in thirteen knots of wind, the average speed dropped to an unacceptable level! In short, the breeze which shifted round to
the North last night lost pressure and was forcing the crew to bury into the Saint Helena High...
"We have just gybed
onto starboard tack to the SW, at 90° to the direct course, which is distancing us from the goal but will enable us to reposition
ourselves in the warm front where there is more pressure. We already have 17 knots of wind, rather than 13 knots half an hour
ago... In addition, it's a nice little move that will allow us to gain ground on the routing. We will be inside the timing
of Orange II as we pass the longitude of the Cape of Good Hope by holding onto the lead we acquired at the equator"explained
Yves Parlier at the radio session this Saturday lunchtime.
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Exchanging the little train for the expressThis little counter move was only to last an hour and a half in the end, the time to track down the pressure and enter into
the warm front. As they approach the roaring 40's, Groupama 3 will engage itself on the fast track to the Deep South: `the
expressway' will give way to a `train' of depressions, which constantly circulate around the Antarctic. The aim then is to
hook onto the right 'wagon' in order to be carried along for as long as possible before the front of the disturbance. Indeed,
conversely to the Northern hemisphere, which is blocked by land around the Atlantic and the Pacific, the austral latitudes
are not disturbed by any land mass (other than a confetti of islands like Crozet or Kerguelen) all around the white continent.
The only bottleneck is 300 miles long and separates Tierra del Fuego from Graham Land, the passage of the dreaded Cape Horn!
A disturbance can therefore occur over Argentina, dropping down across the roaring 40's, slipping along under Africa and running
as far as the South of Tasmania, or even heading back to South America again as it is compressed in the Drake Strait... This
also explains why the disturbances in the Deep South are generally faster than those of the North Atlantic and their movement
can reach 25 to 30 knots, which is exactly the kind of averages that Groupama 3 wants to hold onto!
"We're looking
to pass as close under the Saint Helena High as we can, so as soon as we see the wind dropping, we're gybing to avoid burying
ourselves in this high pressure. The other tack allows us to find wind but it's not on our course... We're also seeking to
get caught by a low, which will carry us as far as the 40's but it will overtake us. Another disturbance will then push us
into the current of the Deep South tomorrow morning" concluded the navigator of Groupama 3. And in fact it is this second
low, which will accompany the high speed trimaran far beyond the Cape of Good Hope, and probably as far as the Kerguelan Islands,
or more!"
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