The first of a number of insights from one of Gavan's mentors, Henry Lupton. Here Henry explains just what the VMG is on the tracket app when following Gavan.

The red line is the rhumb line or shortest distance from start to finish. It is curved because, like airline routes, the shortest distance is a curve northwards (in the northern hemisphere) and it's shown on a two dimensional map or chart.  They go at this time of the year because the sea temperature has dropped below 26 degrees which is the minimum needed for a hurricane to form. They go from the canaries because the prevailing wind is NE in this area just as it is SW around Ireland. The prevailing wind or Trade Winds have been used since Colombus went from La Gomera because most boats can't go directly into the wind.

 


The reason they have gone south of the shortest line is that over the years it has been shown where the highest probability of favourable wind blows in a given area in the ocean. Gavan has chosen a strategy to go quite far South. He is better to go wide early on and then close in on the end point later.


The VMG figure on the leaderboard is Velocity Made Good. This can be confusing.  It is not actual boat speed. If the end point is west of him and he is travelling south west then only part of his boat speed is in direction directly towards the finish. So he could be doing 4 knots boat speed south west but his VMG might be 2.5kts towards the ultimate endpoint.  If he was doing 10knots towards Africa he would have a VMG of -10kts. So the speed only equals VGM if he is pointing directly at the end point.