Bucking a ‘black-hole’

In astronomy, a black hole is a region of space where gravity is so intense that even light can’t escape from it. During the 1986 Newport to Bermuda Race, we ran afoul of a cold eddy that had a similar effect on Matador, an 84-foot maxi boat that was second to finish.

As navigator for Matador, I experienced a bizarre and frustrating dilemma when we were drawn into the grip of this black hole cold eddy. This was despite the fact that this particular cold eddy had dominated my pre-race planning that began three months in advance of the race. Throughout this planning I received NOAA satellite data on the surface temperatures of the Gulf Stream two or three times a week, depending on availability of observations. This cold eddy was a prominent feature, and I anticipated that its slow movement westward would bring it near to our planned rhumb line. If so, it could be a considerable help to us, or it could hurt us terribly, depending upon how we sailed in its vicinity.

Therefore, in March I began focusing on this cold eddy, extracting the position and size of the eddy from NOAA interpretations of satellite data. I had considerable experience with this sort of data from some years of navigating the annual St. Petersburg to Fort Lauderdale Race. In that race, the position of the westerly edge of the Gulf Stream south of the Florida Keys, specifically Rebecca Shoal Light, was critical. If the edge is near, you must sail to it even if the heading is nearly perpendicular to the rhumb line. Conversely, if the edge is far, you must not waste time and distance seeking it. Unfortunately, up-to-date satellite data was frequently unavailable, usually because of cloud cover during the satellite pass, and making a critical decision on old data was always chancy. The consequence was that I had long experience, much of it frustrating, in trying to understand, interpret, and extrapolate the sort of data that was now crucial to our Bermuda race success.

To bolster confidence in the Gulf Stream analysis, Bill Koch, Matador’s owner and skipper, and Vincent Moyersoms, who managed the Matador program, had commissioned a group at the University of Rhode Island to provide an independent interpretation of the satellite and other data. Also, when race day finally arrived, at the pre-race briefing, Jenifer Clark, who then worked for NOAA, presented her explanations and analyses of the entire Gulf Stream situation.

A further, very specific effort to gain information on the eddies involved Bill Koch’s 90-foot sail yacht, Jayhawk, which had made the passage from Newport to Bermuda a few days earlier. Jayhawk had planned to sail directly through the cold eddy and relay her observations to us. Unfortunately, gale-force winds prevented Jayhawk from traversing the critical regions of the cold eddy, so we did not have the benefit of that direct information on the position of the eddy. Nevertheless, by the start of the Bermuda Race on Friday, I felt confident that I knew enough to make best use of the strong currents of the cold eddy that was the focus of my attention.

Warm and cold eddies

The presence of warm eddies has been observed and understood for many decades. Instabilities of the Gulf Stream result in bulges that, when they become large enough, are “pinched off” and become independent entities with clockwise angular momentum. Cold eddies have become known more recently. These eddies are similarly caused by intrusions of cold shelf water north of the stream being cut off and forming eddies. Once generated between the Gulf Stream and Bermuda, a cold eddy moves slowly westward/southwestward with a lifetime of perhaps six months to two years.

The most important feature of a cold eddy is its strong counterclockwise angular momentum that results in currents of two to three knots, and sometimes even greater. A current of nine knots was reported in the 1984 Newport to Bermuda race. Thus, for a boat sailing SSE for Bermuda, there is a big plus in sailing right through the western part of a cold eddy. The game is to determine where the eddies will be when you reach their vicinity and then navigate to reach the proper sector.

The actual situation we faced is shown in the illustration on page 108. The position of the various eddies of the Gulf Stream and Matador’s planned track are illustrated in the illustration. The ocean features are based on Tuesday, June 10, satellite data, whereas the race start was Friday, June 13. Of course, the satellite data gives only the temperature of the top half millimeter of the water’s surface, so there is no actual data on the ocean current itself, except by inference. As shown, the temperature contrasts were dramatic, indicating a maximum Gulf Stream temperature of 79° F while the cold eddy that was to give us problems was a mere 70° F. At Brenton Reef, the water temperature was only 59° F.

Our Matador race strategy was to follow our planned track in order to secure entry into the Gulf Stream well west of the rhumb line. This would ensure that the stream would not set us too far east, especially if the winds became light. Further, according to our plan, it was essential that we exit the stream about 10 miles west of the rhumb line so that we could reach the favored west side of the cold eddy.

The need to exit the stream well west of the rhumb line so dominated my thinking that we let a prime competitor, the maxi boat Boomerang, gybe early and temporarily gain distance to the mark. We stayed with other competitors to enter the stream on starboard gybe to enter the stream farther to the west than Boomerang. Then we gybed to port upon entering the stream. The speed of the stream would bring the apparent wind forward on the port gybe for better speed. This speed increase would be significant if the wind speed decreased as anticipated. Then we would have the benefit of both the current and a more favorable apparent wind angle. As it turned out, the wind decreased somewhat but not enough to give us an advantage over Boomerang. Therefore, all maxi boats were in the same general area upon exiting the stream at the end of the day on Sunday.

Our first frustrations began late Sunday afternoon with Bermuda still bearing approximately SSE. The wind was slowly backing from SSW to SSE at four knots. We were then beginning to see a NNW set of 1.5 to 2.5 knots. This is the worst of all worlds for all sailboats, including the giant maxi boats: extremely light air and an adverse current. We tacked to port, but the leftover waves from the earlier breeze allowed no progress, and we tacked back.

To the masthead

What was happening? Where was the southerly set of our cold eddy that I had been tracking for three months? I went to the masthead, 180 feet up, in hopes of seeing some shear lines, perhaps from floating kelp or debris as in the Florida Straits, or some other indication of current structure, or perhaps a stronger wind in the distance. In 15 minutes I could discern nothing. Back on deck, I explained to the watch that this must be the undefined, unpredictable region between the easterly flow of the Gulf Stream and the counterclockwisehere westerlyflow of the cold eddy. Our competition was generally with us, so we stuck it out on starboard. This meant that we were sailing southeasterly toward the expected new backed wind direction, which was good, but stemming the current from the ESE, which was bad.

At 2300 Sunday night, I awoke to find us still stemming the current, which was now WNW at 2.7 knots with our heading SSE. Wind speed finally increased to eight knots. At this drowsy moment, one of the joys of Matador’s full equipment, the radar, became a liability for me. The radar allows precise tracking of competitors, which is always of great interest to those on watch, but this soaks up a lot of the navigator’s precious time. Thus, it was some minutes before the true picture of our plight emerged in my mind. We had entered the cold eddy in its dreaded northeast quadrant. This meant that if we continued to stem the current setting us to the northwest, we would later be confronted with a strong northerly set. A no-win situation!

I discussed the data and conclusion with Bruce Kendall, the watch captain on the mid-watch. The only alternative was to tack, but with the NNW set, port tack would give us nearly zero speed of advance toward Bermuda. We tacked to port at 0043 and our speed over the ground (SOG), increased from four knots to nine knots. Hooray! Except our course over the ground (COG), was initially 260°, whereas Bermuda bore 148°. We were headed back to Newport.

On radar it looked even worse, as most of our competitors were still heading for Bermuda. The watch captain could not stand it, so at 0100 we tacked back to starboard with COG of 062° and SOG of 4.1 knots. The performance was betterat least we were headed away from Newportbut the future prospects on the wrong side of the cold eddy were terrible. Also, several of our competitors who had tacked to port after we did so were still going west on port. This time, I could not stand it, so at 0124 we tacked a third time.

Now on port we were slightly lifted making COG of 231° and SOG of 7.4 knots. Not great if your destination bears 148°, but at least we were escaping from the fatal clutches of the northeast quadrant of the cold eddy.

Now the reassessment. Where had I gone wrong? After planning so deliberately and working so hard to reach the favorable quadrant of the cold eddy, how could we miss so badly? At this time, about 0200 Monday morning, I concluded that the cold eddy was significantly southwest of its anticipated position, but I did not yet have sufficient data to prove it.

Before dawn we were further lifted on port tack and the current had decreased, so we were making real progress toward Bermudaand toward the center of the cold eddy. The currents in a cold eddy are near zero at the center, increasing with radius. Sure enough, by dawn the current was less than half a knot. Suddenly, the current shifted from a westerly set, as it had been all night, to an easterly set, and began to increase. We had sailed directly through the eye of the cold eddy.

A ring of clouds

When I realized this, I studied the clouds more carefully. We were in the center of a ring of uniform, low cumulus. I guessed that these clouds were generated by the sharp temperature contrast at the edge of the cold eddy. I asked Bruce, now back on forenoon watch, how far away he judged clouds to be, and which clouds were closer. Bruce’s estimate coincided with mine: 20 to 30 miles with us at the very center.

Further, the water temperature had been decreasing from a high of 81° F in the Gulf Stream to a low of 72° F just before reaching the point of change in current direction when we fixed ourselves at the center of the ring of clouds. Since our Gulf Stream maximum was 1.3° C higher than predicted, it seemed that we could be at the center of the cold eddy with 72° F instead of the predicted 70° F.

To further confirm the position of our cold eddy, Bill Koch and I developed a tracing of the current distribution to be expected in a cold eddy. Then we matched this tracing to the observed currents along our track. This analysis showed that the cold eddy structure was as it should be but it was 27 nautical miles southwest of where we had expected.

Perhaps the surface temperature distribution as observed by satellite did not correspond well to the current distribution. Or perhaps the cold eddy moved more rapidly and more southerly than anticipated. After all, it was now six days since the satellite obtained the surface data. With this picture, everything fitted, everything was nice.

But was it? Now I realized that we were still in the grip of the cold eddy. The wind was decreasing, dropping to three knots at 1100, and it was almost on the nose. The current was increasing and becoming more northerly, reaching 2.6 knots with set of 060° at 1100. Bruce and I commiserated. Unless the wind increased soon, we were in real danger of remaining trapped in the cold eddy and being swept north. In fact, if we were fully becalmed, we would be swept back into the same trap that we were in the preceding evening. And the wind was getting lighter. I suspected that, in the absence of any large system wind, we were at the mercy of the thermal wind that generated the ring of cumulus clouds, and that this plus the current might keep us trapped in the cold eddy.

At this point, I felt a little guilty about ever pooh-poohing the nonsense about “the Bermuda Triangle.” Here I was, with my sextant and all of the world’s finest 1986 electronics: multiple loran units, satnav, radar, weatherfax, gyrocompasses, seawater temperature recorder, and accurate sensors with microprocessors which could display the current set and drift directly. With all of this, we were able to define exactly the structure and position of the cold eddy and to predict what it would do to us and how we should try to escape.

But what if I had been in a tiny boat without sophisticated electronics? Could I have figured out what was happening? Might I have concluded that there was indeed some ominous force into whose malevolent grip I had fallen? A black hole in the Bermuda Triangle?

With the wind still light, our fate remained uncertain. We had raced Friday, Saturday, Sunday, and half of Monday in one of the world’s fastest sailboats, and yet we were only 60% of the way to Bermudaand we were about to be sent north again by the cold eddy.

Then at noon, the breeze began to build from the southwest, with boat speed increasing to 9.4 knots at 1300 and 10.5 knots at 1500. Goodbye, cold eddy!

Matador continued with a strong breeze to the finish. For the final 29 hours, Matador was in sight of Nirvana, whose longer waterline gave her excellent reaching speed. The two maxi boats were, however, hard on the wind after passing Kitchen Shoals, and this favored Matador. Matador finished three minutes and 37 seconds ahead to save her time on Nirvana by 27 seconds and to give us first placewe thought.

Condor of Bermuda, however, had finished two hours earlier, thus putting us in second place. Condor had taken a more westerly course at the start, which carried her into better winds initially and which may have allowed her to miss the agonies of the cold eddy.

Nils Muench is an ex-submarine officer with experience navigating an aircraft carrier in the days of sextants. He races his Beneteau One Ton Moonraker on the Great Lakes and has navigated various vessels for skippers such as Lowell North, Dennis Conner, and Bill Koch.

By Ocean Navigator