Volvo Ocean Race 2014-15 - Behind the numbers

by Gonzalo Infante and Jonno Turner on 28 Oct 2014 Volvo Ocean Race 2014-15 - The boats are sailing closer than ever - but while it's exciting, it's not always easy to follow.

We've been inundated with questions about the tracker and rankings, so we asked our in-house meteorology expert Gonzalo to explain the theory behind it. Take it away, Gonzalo.

One of the most fascinating parts of this type of sailing is the art of finding the fastest route to the finish, whilst also preserving the integrity of your crew and boat. If we were living in a world where the wind was always constant, it would just be a matter of geometry - but it's not that easy.

Weather systems move over the oceans, just like the wind does, and that makes the game way more interesting. A good comparison is with mountaineering.

You've got your thermals, and you've got your flask of coffee - but if you plan to ascend a huge summit, like K2, it's important to remember that the shortest distance will not necessarily be the fastest.

There will be crevasses, avalanches, cliffs, and many more obstacles that could block you direct way to the top - and as such, much more distance will need to be covered in order to succeed.

In that way, offshore sailing is very similar.
Yes, there's the most direct route - but you could come across a number of factors slowing you down, or seriously threatening the integrity of your gear, or worse, your crew. Light wind areas, head winds, unmanageable storms and icebergs are just a few on this list.

At the moment, the principle obstacle facing the fleet is a big high pressure system, known as St Helena High. Now, to take the most direct route, would also take the boats directly through its centre - and this is a no-no, a well-known parking lot amongst sailors.

So, in order to avoid drifting across the light wind areas in the centre, the option is to head south - a course that is 45 degrees away from where they actually want to go - which can cause confusion in the ranking calculations.



Sometimes, you might need to sail even more than a hundred degrees the wrong way, or even totally away from the finish, in order to pick up a more favourable breeze or avoid a hazard.

Additionally, the weather systems move, so the 'best' routes aren't always in the same place, they're constantly moving.
So, with so many shifting and evolving variables, how do we know who is leading?

Well, that's a good question! And it's a difficult one to answer. In truth, it's never black or white, as every situation brings different approaches. Sometimes, your race will be to the south before turning to the east, like in this case, because the highway to Cape Town is far south, while other times it might be different. Yes, it seems a bit complex, but it is actually quite fascinating.

'But how do we know, from our sofa, with limited information and knowledge who is leading?', I hear you ask.
And even more importantly, which criteria do the race organisers use to generate a provisional ranking?
Here's a rundown of the measurements on the tracker:

Distance to finish
This is basically the shortest distance approach. Yep, the provisional ranking is no more than calculating the distance to finish for every boat, and putting them in order. It's not always the most meaningful, and it does require some interpretation - but it's simple.

Imagine that you're a Volvo Ocean Race game player, and choose the direct route from Fernando de Noronha to Cape Town. Your best mate tells you that he read an article on the website which says that it's faster to go south first, and so this is what he decides to do.

Over the first two days your Distance to Finish will decrease way faster than his, and your position in the gamers ranking will go up by 1000. You're laughing! He's so dumb.

But wait - suddenly, at day three, your speed starts decreasing and at some point almost all the fleet is heading east, towards Cape Town smashing miles at 25 kts, while you are stuck in the middle of nowhere, in zero breeze. He's had the last laugh.

We don’t show much of DTF in the dashboard, as it's a big number and we're more interested in smaller variations. Instead, we use Distance to Lead, which is basically the DTF distance between the leader and each other boat in the fleet. It's often more interesting to see the rate at which this number changes, than the actual number.
This is what is called 'Distance To Lead Change' or, in simple terms, gains and losses.

Let’s look at another example..
Last Friday while I was having dinner with my family, a friend called me - he was very sceptical of the gains that we published in the last position report. Some boats had gained over 30nm in just 3 hours! Without more information than that he was thinking that the chasing boats should have gone 10 kts faster over the last 3 hours to make such a gain, but that was not very likely. Turns out, he was right, but the numbers were too. They just need a little more interpretation.

Let's do some maths:



The first part of the graphic above shows the relative position between Team Vestas Wind and Team Alvimedica on Friday 24th October.

To calculate DTF we use:
DTF = Distance to Fernando de Noronha + Distance (Fernando de Noronha to Cape Town)
To simplify things, let’s consider that there are only 2 boats in this race and Team Vestas Wind is leading. The numbers are:

So Team Vestas Wind is 135 nm ahead according to our calculations, in pure Distance to Finish (DTF) terms.

The situation 6 hrs later is slightly different: Team Vestas Wind has crossed the waypoint of Fernando de Noronha and Team Alvimedica is still pointing towards this waypoint. This has an impact on DTF since the calculation will be different.

DTF (ALVI) = Distance to Fernando de Noronha + Distance (Fernando de Noronha to Cape Town) DTF (VEST) = Distance (Boat position to Cape Town)

Now Team Vestas Wind is only 89 nm ahead, which means that the change in Distance to Lead (DTLC) has been nothing short of 45 nm! Does that mean that Team Alvimedica has gained 45 nm?

Well, in pure Distance to Finish terms, yes - but, this doesn’t mean much as we know that the boats can't sail directly to Cape Town after Fernando de Noronha, and must sail south to avoid the high pressure centre.

In this case, a much better ranking indicator would be the distance north to south, and you can use your distance tool in the tracker to find that out.

Obviously this criteria will change, as when they arrive to the good westerly winds, they will change direction, so we cannot always use it.

It's complicated, it's strategic - but hey, that's why we love this sport!

Just remember this key information every time you look at the dashboard - and next time someone is heading away from the finish line, ask yourself Event website