Tuesday, November 29, 2005

The way the wind blows

Those of you with eagle eyes will have noticed that the picture below came and went in the time it takes for a tropical squall to come and go.

The reason for the wobble was a sudden worry - was the arrow going the wrong way? For surely, surely winds rotate clockwise round a high pressure system, don't they? And if thats the case then surely the arrow should point the other way round.

Yes the wind does rotate clockwise around a high - if you're in the northern hemisphere as of course London is. Here it is simple:
High pressure = anticyclone = winds rotate clockwise
Low pressure = depression = winds rotate anti-clockwise.

However southern hemisphere all is reversed, so that:
High pressure = anticyclone = winds rotate anti-clockwise
Low pressure = depression = winds rotate clockwise.

So the picture above of the south Atlantic, with the high to the north of the low would result in winds being funnelled between them, blowing a good westerly wind that the Volvo fleet have been enjoying for the last few days.

Few! Got it right after all!

Tuesday, November 22, 2005

Who's ahead?

Well this is interesting. According to Yachting World Brazil is ahead of Ericsson in the Volvo Ocean Race, but according to the official web site its the other way round. The reason for this uncertainty is that actually no one knows - it depends how you measure it, as you can see in the Virtual Spectator plot below.

In this piccy ABN-1 are way ahead to the south. The bright green line is the advantage line which connects all the points as close to the finish as the lead boat. The finish is to the right, to the east, so the line is nearly north-south.

Brazil is the blue dot to the east of the trailing group at the top. As it is furthest right it could be claimed they are in second place as they are nearer to the green line than any other boat.

But then again all the boats are heading south, and in this direction the Ericsson orange blob is ahead of Brazil. So in that case it is Ericsson that is is second place as its got further south than any of the trailing pack.

Who is right? It depends upon what happens next. At the moment the high is close to the Brazilian coast, but soon its due to move away, possibly opening up a passage between weather systems accelerating the boats that are in the right place at the right time towards the finish line. At some point the wind will back more and more westerly and the boats will veer off.

One way of looking at it is if Ericsson beared up to the wind and Brazil followed suit when it got to the same latitude who would be ahead. I think it would be Ericsson - just. So I think its Ericsson which is second. But the key now is to steer for boat speed, to get as quickly south as possible. But if you can get the same boat speed by heading a little more easterly then go for it. Brazil is playing its cards well and I'm sure Neal is looking over his shoulder anxiously.

Monday, November 21, 2005

The road south

The lead four Volvo boats have now passed the way point of Fernando de Noronha and are free to steer straight for Cape Town. But they have not, they are heading south as fast as they can.

You can see why in the weather chart from Virtual Spectator figure below.

The South Atlantic high, that often resides close to the island of St. Helena, drives the winds hard on the nose of any boat that would try the direct path. So it's faster to head south till its time to turn to port. But when? thats will be the next question for navigators to ponder over, when to turn?

But that decision is not yet, as for the next few days they'll be following the same track one after the other with few opportunities to pass. Pure boat speed will drive which boat comes 2nd, 3rd and 4th. But not 1st, where ABN-1 has a clear 80 miles over Ericsson.

Friday, November 18, 2005

Bye Bye Twin

There is a clear leader in leg 1 of the Volvo ocean race - ABN AMRO ONE. The last two days they have sprinted into a 100 mile lead, but how?

Two reasons spring to mind. Firstly by gybing later they paid the price of greater distance but gained the prize of higher pressure. If you look at the stats on Virtual Spectator at 17:00 on 16/11/05 the average wind speed for the ABN twins was around 18 knots while Brazil, then in the lead, it was only around 11 knots. And ABN-1 used that to boost their VMG by a couple of knots, taking the lead away over that night.

And to just kept on going. For there was more than just positioning as ABN-2 at dusk was side by side but by dawn fell back to last position. Its sister ship seems a bit of a flyer, maybe using the new technology better, or having used well the chance to train and test ideas against her twin.

Bad news for the other competitors. They might hope ABN-1 get bogged down in the doldrums, but as the Transat Jacque Vabre showed, these can be transitioned quickly at the moment, and the Volvo fleet seems to be heading for a similar crossing point that got Ellen and the Open 60s through with so few problems.

But there's still a long way to go and the route past Fernando de Noronha when many will remember the last time and the old saying of if in doubt head south. Or less prosaically head south to avoid the St Helena high.

Tuesday, November 15, 2005

Erratic Ericsson

What's up with Ericsson? Today they've gybed 12 times which no one does given the effort and distance lost each time. Is another keel experiencing problem?

Oh, and the ABN twins - they did gybe, just as predicted

Gybe ho!

Yup, as forecast by Captain JP last night the Volvo fleet has began to gybe onto port tack to head deeper south. So far just Brazil and Ericsson have taken the plunge (Ericsson strangely changing its mind many times) while the ABN twins are heading increasingly west. As they find the wind veering further east they too must soon follow suit.

Monday, November 14, 2005

Following the fleet

Long distance ocean racing is not for the comfort loving or faint of heart. To become a slave of the cult for VMG(*), changing sails night and day, watches repeating like clockwork, smelly bunks where you grab too short naps, bad food and worse heads, all is sacrificed for the endless pressure for speed whatever the time or weather, continuous day after day for weeks on end.

And thats just when things are good, when things aren't breaking for against the power of wind and wave even carbon fibre can crumple, and the mere human flung like dolls across cockpit at the mercy of the extreme loads on spars, ropes and sails.

But it is gripping too - to battle against the forces of nature, to use technology, brawn and brain to overcome the elements and competition across the wide oceans to win both trophies and pride. So its great to be able to taste the excitment and thrills while staying in the warm and comfort of home.

The web has proved a natural home for following the far flung fleets. A typical plot is shown below taken from the Transat Jacque Vabres. It shows the lead Open 60s as of 14th November 2005. You can see their direction, track, and route line. This site is better than many as you can overlay the wind direction and strength for the next few days.

This helps you appreciate the race better by seeing the tatics played out in front of you. So Jean and Ellen are both heading nearly due south - why? Well they are entering the doldrums so it could be local conditions - squalls to avoid. But it could also be to get a better wind angle when they emerge from it so they can reach towards Brazil.

But this level of information has been blown away by the absolutely amazing Volvo free software Virtual Spectator. This gives a 3D interactive tool which shows boats sailing under moon and stars, linked into instruments and database of positions.

It's not just good to look at, it really does give a better idea about what is happening. It was clear from VS that Ericsson had had a minor problem because their track paused for about half an hour - just what you'd expect from the "issue with a sail and a halyard" admitted to a day later. And by overlaying the fleet's position, wind direction and tack you can think yourself into the navigator's head as they ponder the big question of the day: when to gybe?

Must be soon.

(*) VMG = Velocity Made Good - how fast you are going in the direction of the destination

Saturday, November 12, 2005

Racing through the vortex

I've twice sailed the seas around the Canary Islands and both times thoroughly enjoyed it. Its warm without being hot and with good winds - most of the time. The first time I sailed there was a week on one of the Challege 67 boats pottering between the islands, while the second was the start of the Atlantic Rally for Cruisers, or ARC, heading out across an ocean to reach St Lucia 3 weeks later.

But for ocean races it's often just an annoying obstacle. The Transat Jacques Vabre fleet had to pass these islands on its way to Brazil recently and yet again some of them were caught out unawares. For though the wind can blow well it can also disappear, and from sea level it's sometimes hard to predict where and why.

But from space the reason is clear as can be seen in the satellite photo below.

This picture shows clearly what are called von Karman vortices. These naturally form when a fluid flow is disturbed by an object, causing vortices to form alternately on either side down stream. In this case the object is the volcanic peaks of the Canary Islands and the flow is the trade winds from the North East. The result is disturbed air, especially to the South East.

More on this effect can be found here.

From watching fleets from the Volvo to the Global Challange the message is often quite simple: keep clear of islands with high mountains. Or see your position drop down the vortex.

Wednesday, November 09, 2005

Pieces of orange

This is what can happen to a multi-hull when flipped by a storm. In this case its Project Orange, which got hit by the legendary bad weather of the Bay of Biscay at the start of the Transat Jacques Vabre.

One reason I'd rather be in a mono-hull when the going gets rough.

Tuesday, November 08, 2005

Sail Away

And they're off! Not one but three ocean races have started recently.

The biggest of all, the Volvo, had its first leg this weekend. This is the fully crewed, multiple stop round the world yacht race with a history going back to the seventies, when it was known as the Whitbread. Then it was near amateur, with proper galleys and space for bottles of wine. Now it is intense full-on professional, with hot bunking and freeze dried food. Now also there are inshore legs, to bring a bit of instant fix for the following media.

First blood went to Ericsson skippered by veteran Neal McDonald who so successfully turned round the Assa Abloy campaign in the last race. There is also a new class of boats - the 70 footers - amazing machines. We had the experience of being overtaken by one when doing the Fastnet - beautiful boat.

Then there's the Transat Jacques Vabre, crossing the Atlantic from France to Brasil. This is one of those events known to serious sailors but little known outside. It has a host of names - Ellen MacArther and Mike Golding are just two of the Brits. Already there has been drama with a number of multi-hulls having to retire following damage in a storm. These trimarans are fast and furious, but dangerous in bad weather where squalls can lead to flips and breakages.

Finally there's the Clipper race 05-06, where an all amateur crew pay around 25k pounds to spend a year getting cold, wet and tired. But they escape the daily grind of work and emails, which is forcing this post to finish just here!

(picture from here)