Tabarly's course, winner of the 1964 OSTAR. Click on image to view full screen
The North Atlantic is a physical oceanographer’s dream playground, all the toys are there to be measured, monitored and admired but sailing through it is a difficult task.
The best-known ocean feature is the Gulf Stream, the current of warm blue salty water that flows rapidly north from the Florida straights is pinned to the continental shelf edge by our old friend Coriolis as it flows north through 30 degrees of latitude. The stream makes a graceful turn to the east that begins off Cape Hatterras and completes off New York where the meanders begin to form and grow. Blue in sea colour terms implies very low nutrients, no plankton, hence not much marine life, compared with the highly productive cool water on the Shelf gives a dramatic contrast in bio systems and bird life.
What is not well known is that the very distinct boundary of temperature and salinity, the ‘North Wall’, is dynamically maintained by its amazing velocity of 2 to 3 knots. The transition from warm 25-degree Tropical Ocean to 9 degree Arctic Ocean can be measured over the length of a ship. To confuse the mariner the stream sheds contra rotating warm eddies into the cold shelf waters making progress even less predictable, at the yachting scale the currents are quite chaotic and detailed charts of the flow are required for racing. Sea temperature gives a clue and gps speed confirms the counter currents velocity (vector).
Icebergs from fiord glaciers in West Greenland make their way over many seasons to their final resting ground on the Grand Banks of Newfoundland. Moving south at 20 to 30 miles per day in the shallow 9-degree waters, some of the biggest will run aground for a time and shed a few thousand tonnes.
The International Ice patrol monitors the season for the benefit of shipping with regular air patrols from April to August. The ice limit for safe navigation extends down to 42 North in late June of an average year, but 2005 had no ice season at all.
The Transat 2008 set an ice gate at 40 north in about 50 west, giving 120 miles of safety to southern limit of the ice, the first time an ice gate has been used in an east west race.
There is often no discernible gap between the east going stream and the gnashing teeth of the iceberg zone, which leaves the racer between a rock and a hard place?
The choice is to take the stream with up to 2 knots against, beating at 4 knots, VMG 3 knots say, in the choppy disturbed sea of the stream, resulting progress NIL. Or take the ice zone, play dodgems for a few days amongst the bergs in the fog and dark .At least the oil rigs are fixed and the cod fishing schooners are gone, aren’t they?
Students struggling with their Yachtmaster night class are familiar with two types of fog; on the Grand Banks here is only one type; THICK n Shallow. It is the best example of advection fog you may handily find, warm moist tropical air flowing happily northward has its bottom rudely chilled by the Arctic cold shelf seas resulting in a dense layer of fog that maybe only 30 feet deep extending 1000 miles in each direction. Enjoy.
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