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12 October 2004, 01:05 pm
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2004/2005 Global Challenge
Portsmouth (GBR) - Buenos Aires (ARG)

After an assured journey up the leader board from 9th place last Wednesday, VAIO have taken the lead, but only just - the 2am poll showed Samsung in the lead!
SAIC La Jolla and Samsung have been recorded as exactly the same distance behind the leaders this morning, at 5nm off the pace.

However, with the small low-pressure system to the west turning the winds against this westerly group, the easterly yachts may finally have an advantage as they weave through the Canary Islands with following winds.

SAIC La Jolla, Samsung and VAIO have all recently changed course to find a better wind angle as the headwinds shift onto their bows. In the lead they may be, but BG SPIRIT, Spirit of Sark and BP Explorer are all in search of a Wind Acceleration Zone (known effectionately as a 'wazi') - a historically beneficial 'wind tunnel' that occurs as wind passes between islands, known to occur between Tenerife and Gran Canaria.

In this case, it is difficult to tell which group will have the immediate advantage. Out to the west they are beating into the wind; not ordinarily a particularly fast point of sail. To the east, a Wind Acceleration Zone may sound enticing, but with variable conditions forecast, the benefits could be negligible.

When the wind hits land, it 'backs' (turns left) causing an acceleration zone, in this case, on the eastern side of the islands where the wind coming off the land converges with the wind already travelling across the water. The eastern edge of Tenerife is known to bestow such a zone, and BP Explorer and Spirit of Sark are clearly aiming for this area.

Looking at the 24-hour forecast, however, the variable wind could reduce any potential gains and, in particular, play havoc with another important factor to consider when sailing near islands - wind shadows.

If the wind is approaching from the northeast, a wind shadow will occur to the southeast (the opposite side) as far as ten times the height of the island across the water. Considering the height of Tenerife, the wind shadow stretch up to 20 miles from the island. The landmass effectively blocks the wind, so the opposite side of the island becomes a void, which teams should avoid at all costs.

In variable conditions, the angle at which wind hits an island will change without much notice. Subsequently, it becomes very difficult to predict where the resultant wind shadow will lie and the chances of being becalmed increase.

On board tacticians may well have to endure the role of hero or villain, depending on the direct consequences of bold decisions, but John BASS summed up his team's long-term approach to losing the lead in a leg of this length in his daily log from BP Explorer today:

"We are not down, our lead has been taken but it is early yet. Gambles on the part of the other yachts in the fleet have paid off but as every gambler should know, you don't always win and consistency is the key. We know we can get back the lead and confidence is high in fact we are enjoying the challenge, we don't want it too easy after all."
Event Media (As Amended By ISAF News Editor)
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