OSTAR skippers enjoy the features of the North Atlantic
By Jerry Freeman
OSTAR skippers are very privileged to be able to experience at first hand some of the most interesting features of the North Atlantic Ocean that most people can only read about: the Gulf Stream, icebergs, fog and electric storms.
The Gulf Stream is the best-known ocean feature of the North Atlantic. This current of warm salty water is pinned to the continental shelf edge as it flows rapidly north from the Florida Straits through 15 degrees of latitude. The stream makes a graceful turn to the right that begins off Cape Hatteras and is completed at about the latitude of New York where it flows eastward along 40oN toward the tip of the Grand Banks at 50o West
The ‘North Wall’ of the Gulf Stream (slope about 1 in 200) is a very distinct density boundary of high temperature and salinity that is dynamically maintained by its amazing velocity of 2 to 3 knots. The transition from warm 25oC Tropical Ocean to 9oC degree Shelf Water can be very pronounced. Large meanders often develop in the stream: these become unstable and separate to form clockwise rotating ‘warm eddies’ into the cold ‘shelf’ waters and anti clockwise rotating ‘cold eddies’ in the warm ‘Sargasso’ water.
At the yachting scale the currents are quite chaotic and detailed charts of the flow are published for races such as the Newport – Bermuda events. On the standard OSTAR route higher sea temperature around 16C gives a clue and GPS speed read-outs confirm when adverse currents up to 1.5 knots are encountered, equating to 20 to 30 miles lost in a day’s run.
Observed from the boat, blue in true sea colour terms implies water that is very low in green chlorophyll and phytoplankton, hence not much marine life compared with the nutrient rich and highly productive cold water on the shelf, famous for its cod fishery, birds and whales.
Atlantic Icebergs are composed of fresh water ice that fell as snow 3000 years ago on the Greenland Plateau and in busy years over 2000 bergs are calved from the fiord glaciers in West Greenland. A very small percentage of these bergs survive the long drift in the Labrador current over several seasons to their final resting ground on the Grand Banks of Newfoundland. Released from the melting winter sea ice in Spring and drifting south at 10 to 20 miles per day in the 9oC waters down the eastern flank of the Grand banks, some of the biggest will run aground for a time and shed a few thousand tonnes.
The International Ice Patrol monitors the movement and extent of the icebergs and sea ice for the benefit of shipping, with regular airborne radar patrols from April to August. The ice limit for safe navigation, (Limit of all Known Ice), often extends down to 42o North in late June of an average year but the 2005 OSTAR had no significant ice season.The 2009 Ostar winner Jan- Kees Lampe opted to sail south of the ice in 43o north and reported sea temperatures varying between 6 and 16 degrees. The subsequent seasons of 2010, 11 and 12 had very low iceberg numbers in the race area. The Transat race in 2008 set an ice gate at 40o north in about 50o west, giving 120 miles of safety margin to southern limit of the ice and this was the first time an ice gate has been used in an east-west race.
In bad years there may be no discernible gap between the east going Gulf 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 on the stream with up to 2 knots against when beating at 4 knots, with a VMG 3 knots say, in the choppy disturbed sea of the stream, resulting progress is almost nil. The alternative is to take the short cut into the ice zone and play dodgems for a few days amongst the bergs in the fog and dark.
Radar may locate the large bergs but it will not detect the large floating ice debris known as growlers and bergy bits. The oil rigs are fixed and the cod fishing schooners are gone. Aren’t they?
Students struggling with their Yachtmaster night classes are familiar with two types of fog. On the Grand Banks there is only one type: THICK ‘n Shallow. It is the best example of advection fog you may 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 may be only 30 feet deep extending 1000 miles in each direction and reinforced by mixing in the often strong breezes. The fog on the Banks is at its most extensive in spring and early summer. Jan-Kees Lampe made this interesting video clip of conditions.http://youtu.be/CLPLEGidl9Y to view.
Fog is often encountered in the last week of the race when in the cold shelf water where the key hazards are the shipping lanes on the approach to Boston , the ‘draggers’ fishing on Georges Bank, and the tide rips on Nantucket shoals. The finish line at Castle Hill Light in the entrance to Newport is often shrouded in fog and approaching the steep-to rocky cliffs is only possible with the aid of GPS. Back in 1984, in the pre-GPS era, one boat was lost on the shore at Judith Point after the finish and another had to back track to cross the line at Brenton Reef tower in 50 meter visibility.
Boats seeking to avoid the fog and the cold may opt for a warmer route toward Newport, but they will not have it all easy .Convection currents in the air above the warm water in and near the Gulf Stream produce dramatic cumulus and cumulo-nimbus clouds with associated electric storms and torrential rainfall. Each cloud cell has its own local surface wind field embedded in the gradient flow and can prove to be a very substantial and frustrating barrier to progress. Zero visibility in the rain and dramatic multiple lightning strikes, confused seas and constant changes in wind direction and strength keep the skipper fully occupied in handling the boat.
The last 1000 miles of the OSTAR provide very dramatic and testing conditions for the sailors to keep them busy and take their minds off the rapidly diminishing distance to go.