Two-boat, or not two-boat?

Two red and white Volvo Ocean 65s rip through the sun kissed sea, separated by just meters, rivulets of sweat mingling with flying salt spray as they fight to convert any hint of an advantage into a measurable lead.

Meanwhile, 240 nautical miles away, Vestas 11th Hour Racing and team AkzoNobel are lining up against each other in an effort to break the red boat's hegemony.

For the first time since 2008, Volvo Ocean Race teams are allowed to undertake what's known as 'two boat testing' – that's where two boats pair up to compare and optimise performance before the race – although for the first time this involves competing teams sparring against each other, rather than teams with two boats training in-house.

As productive as this kind of relationship can be, it's not without risk. Having finished first and second overall in the Leg Zero qualification stage, MAPFRE and Dongfeng have clearly demonstrated that they will be among the favourites the round-the-world marathon when the gun goes for real on 22 October.

So why would you help your closest competitor? After all, boxers don't spar with their adversaries before a big fight. Well, as Dongfeng Race Team skipper Charles Caudrelier says, 'it's a game, and if you don't play it, you both lose.'

Naturally, there's a temptation to hide some information while seeking to squeeze your rival for all they're worth. However, in reality, there's no double bluff going on here as performance gains sought by these experienced teams are so marginal that any attempt at skullduggery would be quickly revealed.

Our focus is not on what we are giving, but on what we will get out of this. We will play it open and in a totally transparent way and both teams are going to learn from it

Bruno Dubois

So why go to all this effort when you could just train alone, privately chalking up the miles in preparation for race start? Well, because yacht racing is a complex business.

Boat speed is affected not just by the sails used, but also by the trim of the sails, the position of the stack (sails, spares and food bags), the angle of the keel, the amount of daggerboard used, the person at the helm, the angle of the swell, the strength of the wind, the period of the waves, wind sheer... far too many things to list here.

The benefit of having two identical boats like the Volvo Ocean 65s is that they can be set up in exactly the same way, and then have one element changed while meticulously recording the data for future analysis. After dozens of mind numbingly geeky sessions, all variables can be tested to compile a definitive trim book.

In the One Design era, the boats are all exactly the same and the weather information available to the navigators comes from the same source. The only remaining variables are how you sail the boat and where you position it on the racecourse.

That means that the small details count. A tiny 0.1-knot boat speed advantage over 24 hrs adds up to 2.4 miles per day, a significant advantage in such a close fleet. But even 0.1 knots overstates how important details are.

In Leg 6 of the last race, Dongfeng Race Team beat Abu Dhabi Ocean Racing by only 3 minutes and 25 seconds after 17 days at sea, a win secured by an incredibly small advantage of just two ten-thousandths of a knot!