Titania day 10 update: How did we get here?
Titania
The Dobbs family and friends
Tue 4 Dec 2018 18:11
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16:48:15N 44:56:77W
Distance to destination: 942 Nm
Those of you following the ARC2018 online
tracker www.worldcruising.com/arc/arc/eventfleetviews.aspx will
see that Titania, along with many other boats, did not head to St Lucia in a
'straight line'. There are some reasons for this, and if you're not a
regular ocean-going sailor you might want to know why.
1. Straight lines on the map
If you draw a straight line on a normal Mercator map of
the world across a trans-continental distance, this is not the shortest distance
between the two points. That actually looks more like a curve on the
flat map, due to the Earth being roughly a sphere (for those of you that
are Flat Earthers, bear with me here), and is called the 'Great
Circle' route. You can prove this by using a piece of string stretched across a
globe. If you've ever wondered why to fly to Los Angeles from London, you fly
over Newfoundland, this is the reason!
So, we were never going to appear like we're travelling
in a straight line on the tracker. In fact, the tracker shows the Great Circle
route itself as a black line.
2. Wind
Even if we had sailed down the Great Circle route, that
still wouldn't have helped, as the wind along that route would have been too
light to give us good boat speeds. Titania is quite a large yacht, weighing
50 tonnes (plus all our supplies), and needs a strong breeze to keep her sailing
around the magical 10-12 knots that we can achieve. By going more south at the
beginning of the crossing, we could get into these stronger winds quicker, and
settle onto a faster course.
We get wind forecasts about every four hours, using the
internet via satphone to download GRIB files which contain detailed info about
wind strength and direction. With these in the navigation computer, we can
predict what the wind will be doing as we travel west, and we can make sure we
don't steer into a patch of light winds. Jam today and hopefully jam
tomorrow.
3. Angles to the wind
Sailors quite often go further but faster in
order to get there quicker. We have a number of phrases for this: VMG, dVMG,
VMC... They all roughly mean the same thing: going dead downwind is slower than
sailing with the wind on your shoulder, and you need to know how fast you're
approaching your destination, even if you're not actually pointing at it. We
monitor this through our navigation software, and it's also displayed on the
instruments visible to the crew on deck. We know how Titania sails best, and so
we position ourselves so that the wind is the optimal angle for us. At the
moment we are monitoring our speed in the direction of St Lucia which, happily,
is also the direction in which we are pointing.
We're within 1000 miles to our destination now. We are
doing well against the other boats (not that it's a race, of course...), and
hope to reach St Lucia at the weekend for some rest, recuperation and rum
punches.
Wildlife watch: we were buzzed by a beautiful little
whale today. It surfed behind us, overtook us, went under the boat, swam round
the front of us, and then did it all again. They really do look like they're
enjoying themselves, inquisitive and benign.
Ned
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