Leg Info

赛段起航时间:
2017年11月5日

概要:

11月5日从里斯本启航,从葡萄牙海岸一路南行7000海里后,抵达非洲大陆的最南端——开普敦。这是一次经典的由北往南的大西洋航行,途径多个气候带。

气候带是什么?

地球的海洋性气候以明显的气候带为特色,平行分布并环绕地球,从赤道向两极对称分布。当船队由南向北行进时,将穿越一个个不同的气候带,其中的秘诀就是在每次转变时找到进入、离开气候带的最佳时机,因为条件显著变化时往往对比赛胜负造成显著影响。

有哪些挑战?

副热带高压区(北大西洋无风带):挑战同时意味着机遇,所以在本赛段中有许多制造优势的机会。船队首先迎来的由列岛命名的一个副热带高压——亚速尔高压。

这将是船队迎来的第一个气候带,常年温度在30-38度,大片区域为静态、半静态的高压区。该区域因为高压而导致风力微弱,古时候船长航行至此,因船速明显减弱,在水源缺乏的情况下不得不将死掉的马屁抛出船外,因此得名“北大西洋无风带”。

信风:亚速尔高压同时也决定了第二种海洋性气候带的位置——信风。信风带是吹向赤道的持续强风,在北半球为东北信风,南半球为东南信风。因此在地球上有两个信风带,分别从副热带高压吹向赤道。

一切都取决于亚速尔高压的位置,如果位置不错,船队可以借着信风离开里斯本,并且一路快速南下。但如果高压越过了里斯本,船队将不得不在风力微弱的环境里挣扎前行,这种情况下往往比赛进度缓慢、压力巨大,毫无乐趣可言,除非你是优胜者。

群岛:船队的南下之路上分布着加那利群岛和佛得角群岛,两者都是火山岛屿,且地势较高,影响附近区域的风力、风向达上百英里,这也意味着这里机会多多。

赤道无风带:信风带以南是赤道无风带,也称为赤道辐合带,这一低压区几乎笼罩着赤道地球的海洋。它产生的原因是暖湿气流上升(相对于冷空气),而热带存在大量这样的暖湿空气。赤道无风带常伴有雷雨天气,风力微弱,雨,及突如其来的阵风,总之这一地区随时都有意外发生.

这里为气象知识薄弱的人做点补充,北部或南部吹来的较冷空气进入取代了上升气流,从而形成了北半球的东北信风,及南半球的东南信风。

能否巧妙的穿越赤道无风带在很大程度上决定了本赛段的胜负,因此这会是一段非常紧张的时刻。秘诀就是抓住风力最弱的时机穿越,而这往往更靠西,因此船队会沿着那个方向直到抓住合适时机的那一刻,然后往北追赶。神话曾被创造,传奇的船只会在这条路上走更远,然后快速折返,这个巧妙的时机大概在27-18W,也可宽限至25-30W。

圣海伦娜高压:气候带沿赤道呈南北对称分布。因此,在南大西洋上有个和亚速尔高压相对应的圣海伦娜高压。高压意味着风力小,阻断了船队前往开普敦的路。

船队可能会行进至高压西部,试图在这里取道。大部分情况下绕着高压向南航行总会更快一些,最后抵达最后一个气候带——西风带。

南大洋及西风带:在西风带上,风暴及低压系统由西向东移动。它们环绕北半球的北极、南半球的南极,由西向东运行。航行战略是始终弄清楚副热带高压,然后进入西风带,找到一个向东的低压系统,然后借助它。它会帮助船只加速向东穿越南大西洋,将船队带入南大洋,有时甚至直接带到桌湾。第一个借助到西风带的人通常会赢得胜利。

如此多的机遇,必然铸就过大赢家么?

在1997-98界比赛中,首次参赛的保罗·卡亚尔和他的导航员马克·吕迪格驾驶这英孚语言号大胆选取了与其它船队不一样的路线,从费尔南多迪诺罗尼亚岛南行。这使他们第一个进入西风带,他们借风航行,保持领先,并且一路将优势保持到了最后。

Leg 2 Strategic Review. The south pays... again. The second leg of the Volvo Ocean Race 2017-18 ended with a fine win for Spanish team MAPFRE.
Text by Mark Chisnell

The win came after a smart decision by skipper Xabi Fernández and his navigator Joan Vila to commit to the south as they went around the South Atlantic High, playing the hand out to grab a lead they could defend all the way to the line. 

The move
Let’s go back to the morning of the 18th November in Image 1; 04:46UTC to be exact.

Image 1 - ©Geovoile

Dongfeng Race Team (red) have been leading the fleet for over a week, shadowed constantly by MAPFRE (white). But now, MAPFRE and Team AkzoNobel (purple) have gybed to starboard, splitting from Dongfeng. Vestas 11th Hour Racing and Team Brunel had both spent about three hours on starboard the previous morning, but otherwise, the whole fleet had been on port since a gybe way back north of the Cape Verde Islands nine day previously – so they’d all had plenty of time to think about this move.

The strategy
We covered the strategy for this part of the race in some detail in the third of our Leg 2 Strategic Reviews so I will keep it short and sweet here.

The trade winds and the Doldrums are both climate zones (a concept that’s covered in more detail in the leg preview) – briefly, the earth’s oceanic climate features distinct bands, lying horizontally and looping the globe, running out from the Equator to the Poles in a mirror image. The fundamental idea of these strategic reviews is that the race is won and lost in the transitions between these zones, and that’s exactly what happened here.

South Atlantic High
At the moment of the gybe in Image 1, the fleet were moving out of the influence of the north-easterly trade winds, and into the northerly winds in the western quadrant of the South Atlantic High – an area of semi-stationary high pressure that often stretches across most of the South Atlantic.

In the centre of this high pressure there is very little wind, creating a road block to Cape Town. It’s clearly visible as the blue area to the east of the fleet in Image 2, taken from later the same day, 19:00UTC on the 18th November.

Image 2 - ©Geovoile

The anti-clockwise rotation of the wind that defines a high pressure in the southern hemisphere is also visible (it goes the other way in the northern hemisphere).

The traditional route from here is to continue south, skirting the high pressure until the boat reaches the next climate zone, the Westerly Storm Track, to meet a low pressure system moving from west to east as it circulates the Antarctic. The boats will pick up the new fresh breeze from the low and ride that wind all the way to the finish line.

First principles
However, as you can see from Image 2, things were not that simple this year, with another area of high pressure to the south of the fleet, blocking the direct route to the Westerly Storm Track. Nevertheless, Joan Vila and MAPFRE were about to prove that sticking to first principles – lead the fleet south – would still be a race winning strategy.

Let’s zoom in on the moment depicted in Image 2, 19:00UTC on the 18th November, to get Image 3.

Image 3 - ©Geovoile

Everyone has now gybed, all following MAPFRE to the south, and it’s clear that the boats to the east are already getting punished for getting too close to the centre of the high and the light winds. We can see the tracks of Team Sun Hung Kai and Turn the Tide on Plastic as they gybed back and forth in their attempts to escape the encroaching light air.

Slow to gybe
So it was a surprise then that the leader and pace setter for the previous week, Dongfeng Race Team should hold on to the port gybe until about 07:30UTC. It was only three or four hours longer than MAPFRE, but it was enough for the Spanish team to end up about 90 miles to the south-west of the Chinese.

MAPFRE have much better conditions and speed at this point; 16.8 knots of wind, and 17.8 knots of speed versus 12.2 knots of wind speed and 12.0 knots of boat speed for Dongfeng. This is because they are further from the light air in the high pressure zone.

Fast forward five hours to midnight on the 18th in Image 4, and the fleet has started to gybe back.

Image 4 - ©Geovoile

MAPFRE is one of the last to go, and as they gybe to head east for Cape Town they are almost directly on the bow of Dongfeng Race Team – who by now have clearly recognised their mistake and are trying to get further south to correct the error.

The image tells the story
The story is told in the numbers and the picture – after all, if Dongfeng Race Team had gybed at this point they would still have been closer to Cape Town, and were theoretically ahead of MAPFRE. The leaderboard (which is scoring purely on a boat’s closeness to the finish line) has Dongfeng Race Team in fifth, and MAPFRE 25 miles behind them in last place...

The real story is in the continued difference in wind speeds (18.5 knots for MAPFRE and just 13.2 knots for Dongfeng), and the positions of the blue, windless, high pressure zones depicted in the image. There is the big one to the north-east of the fleet, but there’s also a second bubble of high pressure just to the east of MAPFRE, and this is the one that Joan Vila is focused on getting around cleanly, so they can pick up the low pressure system and front that is to their south.

Let’s go forward another five and a half hours to 05:30UTC on the 19th November in Image 5, and we can now see the big breeze to the south-west of MAPFRE more clearly.

Image 5 - ©Geovoile

Their course is taking them south of the little bubble of high pressure and light winds to their east, while to their north, Dongfeng Race Team, Team Brunel and Vestas 11th Hour Racing are all pointing straight at the danger zone.

Convergence
So it was no surprise to find that 18 hours later – at 00:30UTC on the 20th November in Image 6 – those latter three boats have all been forced to take another hitch to the south to dodge the light air and get into the breeze from the front.

Image 6 - ©Geovoile

This is now roaring into play, big breeze coming on, pushing everyone east and sweeping away the remnants of the high. To get to this wind the immediate chasing pack have been forced to converge on MAPFRE’s course, and have mostly dropped in behind her. The leaderboard now reflects the reality on the race track, with MAPFRE in front of Team Brunel by 22 miles, with Vestas 11th Hour Racing and Dongfeng Race Team a further 20 or so miles behind them. South paid, and some – and while the different areas of high pressure made it more complex than ‘normal’, the fundamental principle of being first into the wind from a low pressure system still held true.

Dropped?
In the previous strategic review we were concerned that the front would now either move ahead of the fleet, dropping them into the high pressure lurking to the west; or fizzle out before Cape Town, and leave the fleet trying to deal with another high pressure zone setting up before the finish. Any boat that was dropped by the front would have to gybe south to find new wind, but the safest strategy for MAPFRE and the immediate pack chasing her was to keep the hammer down and try to hold onto the front for as long as possible...

And they did just that, not without some difficulty, as we can see from Image 7 at 03:00UTC on the 23rd November.

Image 7 - ©Geovoile

Everyone has had to gybe, as the front finally started to move away from them to the south-east, leaving them in a fading westerly breeze. The lead pack of four managed to stay with the wind from the front after the gybe for just long enough to escape the high. They moved into the strong southerly that sets up along the west coast of South Africa as the high pressure came in behind them.

Drag race
The front four found themselves in a straight line drag race to the finish, with MAPFRE finishing on Nov 24 at 15:10UTC with Dongfeng Race Team almost three hours behind at 18:02UTC, then Vestas 11th Hour Racing at 19:37UTC and Team Brunel on 25th November at 00:14UTC. This was a brilliant recovery by Dongfeng who were back in fourth once the fleet had converged, twenty miles behind second placed Team Brunel in Image 6 from 00:30UTC on the 20th November.

I think they achieved this just by good speed and consistent sailing in the big breeze and waves of the cold front. If you look at Image 8 taken just 36 hours later at 12:00UTC on the 21st November, Dongfeng Race Team are already back up into second and leading the chase to MAPFRE. In these conditions at least, it looks like this is a two-boat race around the world.

Image 8 - ©Geovoile

Of course, there’s a lot more to the rest of the race course than the Southern Ocean, and we will see plenty more tactical and strategic opportunities – like the convergent wind line that Vestas 11th Hour Racing found in the Med to take the lead in Leg 1 – to keep the pot boiling and the podium turning over.

Restart and a Fastnet
A final word on the back three, who all had to dive all the way south to find new breeze as they were swallowed by the high pressure. Check out Image 9 from 05:00UTC on the 24th November, with all three boats virtually side by side with 605 miles to go to the finish – about the same distance as a Fastnet Race. The gun goes and the restart starts...

Image 9 - ©Geovoile

They were all on the leading edge of a new low pressure system that was moving east and pushing the light air and high pressure away, keeping them in solid breeze. Nothing much changed for the next 24 hours, they were still within three miles of each other at 08:15UTC on the 25th November in Image 10, with Cape Town to the north-east. The low was headed south-east, and there was a wall of high pressure between them and the finish.

Image 10 - ©Geovoile

Things looked worse than they were, fortunately the high was going east too, and they crept around its eastern edge, eventually ending up dead upwind of Cape Town in a solid 18-20 south-westerly that was slowly shifting to the south – Image 11 from 13:00 on the 25th November.

Image 11 - ©Geovoile

Persistent shift
A persistent wind shift like this is a very straight-forward tactical situation that any dinghy sailor would recognize, and everyone knew what to do – sail until you can make Cape Town on starboard, and gybe. It came down to boat speed, and Team AkzoNobel’s experience was starting to pay. They eked out a four to six mile lead over the other two that they maintained quite comfortably to finish fifth later that evening, November 25th at 21:24UTC.

The fight to avoid the wooden spoon went all the way to the wire with Team Sun Hung Kai/Scallywag eventually shading it, finishing at 21:55 and 21seconds UTC with Turn the Tide on Plastic one minute and eight seconds behind.

Old rules rule
Looking back, it was a relatively straight-forward leg. The fleet were straight into the trade winds out of the start, the Doldrums were gentle on them, and although the South Atlantic was a complex mess as they approached it, in the end the old rules ruled.

So I’ll conclude with the old rule for Leg 3, down through the Southern Ocean to Melbourne: keep going south till it’s blowing 40 knots, then turn left and hang on. We’ll see how well that one works out starting 10th December...


Read the weekly reviews for Leg 2: Week 1, Week 2, Week 3

Here the crew line-ups for the Leg 2 - Lisbon to Cape Town (7,000nm).

Here are some of the best images of the Leg 2.

Leg 2 in 200 seconds. The 7,000 mile marathon from Lisbon to Cape Town had everything – and here's a look at the best of the action: 

Leg 2 in 200 seconds | Volvo Ocean Race

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