Posts Tagged ‘great circle’

Race finishes – close and otherwise

Saturday, February 7th, 2009

Michel Desjoyeaux (Foncia), in winning the Vendee Globe by more than five days from Armel Le Cléac´h (Brit Air), who is due to finish today, reminded me of a very different yacht race finish.

In the 1982 Sydney-Hobart Yacht Race, Condor of Bermuda beat Apollo by just seven seconds, to win the battle for line honours. If you’re not familiar with it, the Sydney-Hobart is a 630 nm race.

The Race Directors of the Vendee Globe calculated the total distance this year, using great circle and taking in the marks of the course, as 24,840 nm. But when Desjoyeaux finished he had sailed 28,303 nm at an average speed of 14 knots. The average came down to 12.30 knots when calculated for the Race Directors’ distance.

For Brit Air to have finished as close to Foncia as Apollo did to Condor, the margin would have been only 4.5 to 5.25 minutes. That would have been truly exciting yacht racing!

Passage planning – the great circle route

Tuesday, November 18th, 2008

When navigating over long distances it’s better to sail a great circle. Technically, these are circles on a sphere (Earth) whose planes pass through its centre. So, the equator is a great circle, and so is a circle through both poles. It follows therefore that any circle between those two is also a great circle. It is shorter to follow a great circle than to follow a straight line plotted on a chart.

Because it would be difficult to steer the constantly changing course that a great circle would demand, it is usually made up of a series of rhumb line courses between waypoints.

An alternative to this would be sailing a circle at, for example, latitude 30º north. This does not pass through the centre of the sphere (Earth) and is known as a small circle, as are any others like it.

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