Map Display

Thursday, 9 February 2017

How far south?

Until the early part of the nineteenth century, sailing ship routes were based not on any scientific foundation but simply on what had worked in the past.

Mathew Fontaine Maury, a lieutenant in the United States Navy at that time prevailed on a large number of military and merchant mariners to pass to him logs of their weather readings during their various voyages. From this, Maury compiled charts showing the likelihood of winds of various directions and strengths in different parts of each ocean.

These charts, updated with modern observations, are available today to assist in the planning of ocean voyages. While day-to-day routing is based on actual weather and short term forecasts, the grand plan of the voyage is based on "Pilot Charts" descended from Maury's original work. From these maps we can tell, for instance, that winds in May in French Polynesia are calm less than 1% of the time and blow from the west almost never - a great region and time in which to make your way west! Similarly, in February in the area in which we now sail, the winds are said to virtually NEVER blow from the east. As sailboats cannot easily make ground directly toward the wind, we would seem to be well positioned for an eastbound passage.

Unfortunately, "virtually never" is not the same as "never"! Low pressure weather systems usually travel around the bottom of the world to the south of the roaring forties reinforcing the west winds prevailing in this region. Nonetheless, in the warm sub tropic waters far to the north of us a complex low has chosen to develop. It now plans to move to the southeast across our path and produce gale force easterlies exactly where we would like to be in a few days. As such winds are something we would prefer to avoid, we keep deviating south. On this path, the gale force east winds should lie to our north until the weather system passes to the east and dissipates. We expect to return to somewhat more clement latitudes in a few days after friendlier winds reestablish themselves there.

Of course there are limits to this! Not much to the south of latitude 50, Antarctic icebergs start to be a concern. As the weather situation develops, rather than be forced even further south, we may need a different plan ... perhaps we will simply heave to and wait while the contrary winds howl themselves out to our east.

A negative aspect to our southerly route is the change in cabin temperature from merely "uncomfortable" to "depressingly cool". Yes, we have a very efficient heater aboard but we would prefer to save our diesel fuel for emergencies as our route will take us over 1000 miles from land for a few weeks into the future. As we approach South America in March, we may choose to warm up the boat ... or we may be so inured to the cold by then that we can't be bothered. Notwithstanding this comment about the chill, it is actually the same temperature here at 48 south as it was 250 miles further north on our crossing ten years ago. Could it be that the warmer temperatures this year are leading to the formation of the tropical lows and to the displacement of the wind patterns further south than usual?

As the weather system that has favored us with a fast passage over the past week draws to a close, we have slowed from seven to five knots. From this remote place, far away almost straight north are the islands of, first, Rarotonga and much further again, Kauai. Traveling due east over three thousand miles you find Chile; but perhaps surprisingly, west along this latitude, you find no land at all until the coast of Argentina. Our nearest land, New Zealand's Chatham Islands, is 650 miles behind us and we have sailed almost 1200 miles since leaving Picton just over a week ago.

At 2/9/2017 21:48 (utc) our position was 47°51.25'S 159°57.18'W

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