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HOW-TO Technique

Crossing the Gulf Stream

A better understanding of the legendary ocean current can make your passage faster and safer

The Gulf Stream is part of a current that circles the Atlantic Ocean from the Americas to Europe. Ocean currents are caused by various factors: differences in water temperature and salinity, the varying height of seamounts and the ocean floor, and local winds. The Coriolis force, caused by the Earth’s rotation about its axis, also has a telling effect on this moving river set within the more static waters of the oceans.

Figure 1 shows the various oceanic currents over the North and South Atlantic. From the Caribbean Sea, the stream flows northward through the narrow Straits of Florida, achieving currents as high as 5 knots. The Gulf Stream then continues to roughly follow the contours of the eastern coastline north as far as Nova Scotia and Newfoundland.

The Labrador Current flows southerly from Greenland and Newfoundland. The intersection of these cold waters and the warm Gulf Stream is a factor in the easterly bend of the stream, and is also responsible for the fog seen in the Grand Banks zone. Upon meeting the Labrador Current, the Gulf Stream splits. One branch proceeds toward Greenland, another more toward Iceland, while the primary segment flows almost due east toward Europe. This forms the “north wall” of the stream. It eventually bisects again near the European coast; the northern branch affects the shores of northwest Europe, warming the bitter cold waters there. The more predominant southern branch flows southeastward along the European coast and Africa, becomes known as the Portuguese current, and then turns westerly toward the Caribbean Sea to begin the cycle again.

The Gulf Stream waters actually generate their own mini-climate, as warm air rises and generates distinct areas of low pressure. The Gulf Stream waters are a breeding ground for many of the severe storms experienced by those living along the eastern seaboard.

Anyone crossing the Gulf Stream from east or west, or across the north wall, is advised to exercise caution and careful planning to ensure favorable conditions. When done properly and rough weather is avoided, the major concern becomes the prominent set to be expected when the current flows across one’s course.
As the stream varies in width, from about 30 miles off the coast of Florida to more than 80 miles farther north, it pays to make crossings at the narrowest point within a reasonable distance of the course line, and to make good speed while doing so to lessen the current set and to get across before inclement weather can develop. Whenever current flows against wind, waves can build quickly and become steeper than normal. In this manner, waves in the Gulf Stream grow precipitously in a short span of time, within hours, after a strong opposing wind develops, as seen in the photo on the left.

Wind of less than around 20 knots, even out of the northern quadrants, can make sailing uncomfortable, but don’t usually cause dangerous waves. The key is to avoid the Gulf Stream current when wind out of a northern quadrant in excess of 15 knots blows against the direction of the current. These winds can result from a low-pressure system, passage of a cold front, or interaction between high and low pressures.

The other important consideration involving the Gulf Stream is the eddies that circulate around it. Figure 2 above shows that warm water eddies are often seen north of the stream, and cold water eddies develop to its south. Warm eddies circulate in a clockwise direction; currents around cold eddies are counterclockwise. The strategy is to position the boat in that portion of an eddy that favors rather than opposes your course line, taking advantage of up to a knot per hour boost in speed for up to 30 hours! At the least, avoid getting caught in the wrong side of an eddy, which slows the boat accordingly.
Consider the directional flow of the eddy waters; if that flow counters wind direction, waves can build much like they do in the Gulf Stream proper, although usually not as much.

When preparing to cross the Gulf Stream, certain steps should be taken. These steps should include the following:

Study the weather
•    Download and interpret weather chart information on your own or get routing assistance from professional services. Concentrate on forecast wind directions at the time you’ll be crossing the stream.

•    Download the latest positions of the Gulf Stream and associated eddies. I have gotten this information from Jenifer Clark’s Gulfstream (http://users.erols.com/gulfstrm) and NOAA (http://polar.ncep.noaa.gov/ofs). Positions of the Gulf Stream proper and eddies change on a daily basis. Eddies generally drift toward the south or southwest, and their positions are only accurate for about three days from when they’re issued.

•    After departure, monitor the weather closely, both by electronic chart downloads, sea buoy data, and by paying attention to local conditions. Do not entrust your forecasts solely to downloaded charts; what you actually experience can differ from those predictions.

Manage your course
•    Allow for the expected set of the current. If the area you intend to cross is approximately 60 miles wide, consider flow in the innermost 20 miles of the current to be the fastest. I usually allot 1 knot per hour of set from my course line, and compensate before entering the current. Calculate the stream width and number of hours expected to cross it, and then enter the stream up current appropriately.

•    Set a waypoint where you’d like to enter the stream to account for current set.

Monitor the crossing
•    Watch the track line as you cross. Don’t be surprised if you make 30 or even 40 degrees off your course line as the current exerts its presence. Do not steer to counter the current set; maintain a course directly across its flow.

•    Monitor the water temperature when approaching, traversing and leaving the Gulf Stream. For example, the sea temperature may be 76.9 degrees F, then suddenly increase to 79.8 as you enter the fringes of the stream. It will climb to temperatures of up to 85 degrees in the middle sections, and then gradually fall as you near the other side.

You may also witness the following in or while approaching the Gulf Stream:
•   Cumulus clouds above the warm waters
•    A distinct line of sargasso weed or difference in appearance that separates the stream from the still ocean waters (as in the photo above)
•   Deeper blue hue to the water
•    Dolphins that follow the stream in search of food will make contact and play with boats more often near the stream
•    Fog can develop if the warm water flows beneath cooler air
•    Localized squally weather

Any boat crossing the Gulf Stream should be well fitted out with storm sails and adequate safety equipment and those on board are advised to know how to cope with heavy weather situations. If done correctly, under the right weather conditions, Gulf Stream crossings are not dramatic events.

In the 29 passages I’ve taken across the Gulf Stream, I’ve only encountered storm conditions on one occasion. I was not then a captain, and would not have sailed were I aware that a strong cold front would approach the area shortly after our departure from New York Harbor. Those three days spent in 30- to 40-foot waves and Force 9 wind provided memories to last a lifetime, and taught a lot of lessons about ocean sailing. Forethought and planning has prevented a reoccurrence of that incredible experience ever since.

Ed Mapes owns Voyager Ocean Passages (www.offshorevoyager.com)and conducts offshore training at sea.

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written by Mark Welles , March 27, 2012

Knots per hour is redundant
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The author of this article is Ed Mapes.

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