Tacticians, Navigators and Skippers in the Newport Bermuda have choices to make in deciding the fastest route to Bermuda. The straight — rhumb line— course is the shortest distance between two points, but it may not be the fastest. Two choices could determine victory or defeat. Will the wind on the course or Gulf Stream current be more important? That choice must be made before the race starts. The 164-boat fleet sets off Friday, June 20 from Newport Rhode Island.
For more than forty years Frank Bohlen has studied ocean and near-shore currents. Since 2002 he has prepared detailed analyses of the ocean between Newport and Bermuda in the months prior to this race. In his recent online tutorials on the race website, he has described Gulf Stream development using images from NOAA and other sources.
Dr. Bohlen commented on the Gulf Stream choices this week. “The Gulf Stream in the vicinity of the straight line Newport to Bermuda route (the rhumb line) has been dominated by a deep meander. The meander has remained nearly stationary and deepened causing the direction of the flows in the main body of the Stream to rotate clockwise to a nearly northwest to southeast flow essentially paralleling the rhumb line for a distance of about 180 nautical miles.”
“The few shots of surface sea water temperatures that have been obtained recently suggest that the meander is the process of “pinching off” favoring formation of a cold core ring south of the main body of the Stream, increasing the development of the warm core feature north of the Stream near the edge of the continental shelf and redirecting the main body Gulf Stream flows to a southwest-northeast course crossing the rhumb line approximately 240 nm from Newport.”
“If this remains unchanged, the Gulf Stream will have little direct influence on optimum course selection. At the moment the warm feature north of the Stream favors a near rhumb line course from Newport to south of 39o N with a slight bias to the west to accommodate some amount of easterly set through the main body of the Stream. The Stream near the rhumb line is approximately 60nm in width with flows proceeding south to north east of the rhumb line.”
“To the south, the westerly edge of the cold core ring presently centered to the east of the rhumb line is in close contact with the rhumb line. This favors a direct course to Bermuda. The ring is expected to drift slowly (2-3 nm/day) to the west so that some additional course alteration to the west may be necessary to take full advantage of the ring currents.”
Bohlen concluded, “The combination of these Gulf Stream current features favor a course west of the rhumb line, with exact details dependent of boat characteristics and wind speeds and directions.”
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