Without a doubt, the Gulf Stream is the most discussed and publicized ocean current in the world. Through the years there have been as many theories as to its origin and properties as there have been scientists and mariners concerned with its study. Certainly there are almost as many theories concerning the conduct of a vessel in its influence as there are masters of vessels sailing its waters.
However, with the development of new electronic navigational devices, more can be learned of this great current in less time than heretofore. This article discusses the possible saving of time for vessels in the Stream by means of frequent and careful fixes. It therefore, deals with the conduct of vessels in the current, rather than a more academic analysis of the stream.
In the early morning hours of March 29, 1949, the motor vessel Wanderer, a 450-ton vessel with a standard speed of 9.8 knots operated by Sperry Gyroscope Co., as a test ship, was on such a course as to intercept the charted axis of the Gulf Stream off Carysfort Reef Light located on one of the Florida Keys. She had left New Orleans on March 25, bound for Washington, D. C., and on this particular morning the weather was excellent with no sea and only a slight swell.
As Captain of the Wanderer I planned to remain in the vicinity of the axis of the Gulf Stream as indicated on H.O. Chart 0943, and with the aid of Loran this presented no formidable task. It was with relish that I looked forward to this run, as only those who have commanded a 9.8 knot vessel can realize the exhilaration that comes from doing 13 or 14 knots, in such a vessel.
The task of remaining in the Stream’s axis from Carysfort Reef to West Palm Beach was comparatively simple, as Radar ranges and bearings were used entirely in this stretch. When 16 miles southeast of West Palm Beach, the first good Loran fix was obtained, and from this position to Diamond Shoals Light Vessel, Loran was used exclusively, giving a position every hour with accuracy to within one half mile.
From Carysfort Reef at 0530 hours on March 29 until 0400 hours on March 30, the vessel was maintained within one mile of the Gulf Stream’s charted axis for an average speed of 13.5 knots. By 0600 hours that morning the Loran fix indicated the vessel to be 3 miles to the right of the axis, with a drop in speed to 11.5 knots. Believing that this was a normal drop due to our progress north, no effort was made to bring the ship back to the axis.
At 1000 hours, in Lat. 31° 19' N, Long. 79° 04.8' W, the course was altered to bring the ship an equal distance to the left of the Stream’s charted axis in an effort to find more current. Our average speed remained unaltered at 11.5 knots, and consequently at 1300 hours the vessel was placed back in the axis in Lat. 31° 43.6' N, Long. 78° 36.3' W. By 1800 hours the vessel had covered 62.8 miles in the axis for an average speed of 12.5 knots. Thus, it would appear that by sticking to the axis a full knot was gained over running in a position 3 miles on either side of the charted axis. To add further emphasis to these findings, the increase in speed was encountered in positions 90 to 150 miles North and East of the 0600 position and in a region where, according to most descriptions of the characteristics of the current, a natural tendency to diminish in strength can be expected.
Once again, at 1800 hours, 67 miles south of Frying Pan Shoals Light Vessel, the Wanderer was permitted to fall off to the left of the Stream’s axis and in 4 hours covered 48.5 miles for an average of 12.1 knots. At 2200 hours she was brought back to the axis and an increase of .4 of a knot was observed until 0300 of March 31, when a course was set for Diamond Shoals Light Vessel.
During this entire time there were tank vessels 6 to 8 miles on either side of the Wanderer bound in the same direction. As I became constantly more aware of the results of dropping off either side of the Gulf Stream’s axis, I couldn’t help thinking of that old story of “everybody being out of step but Johnnie.” However, when the Wanderer was allowed to approach their tracks, she lost speed. Yet each master on those other ships was doubtlessly as sure of being in the maximum current as he was of being aboard his ship, the while deprecating the poor navigation of the other vessels as he gazed over them.
Upon return of the Wanderer to New York, the log of its northbound voyage became the subject of intensive study. Positive proof voiding or confirming the tale told by the log could not be found. It was obvious that confirmation of an apparent higher velocity within the Gulf Stream must come from additional first-hand observations. It was then that a Loran receiver was installed in September, 1949, aboard the S. S. Esso Concord through the cooperation of the Esso Shipping Company. The Esso Concord is a 12-knot tanker regularly employed between Gulf ports and New York.
Results aboard this vessel bore out fairly closely what had been observed aboard the Wanderer. Up until 1227 hours on September 21, 1949, the vessel had been maintained in the Gulf Stream’s axis for an average speed of 16 knots. At 1327 hours, in Lat. 27° 52.5'N, Long. 79° 40.3' W, a Loran fix indicated she was 3 miles to the left of the axis; and from that position, until 2105 in Lat. 30° 05.2' N, Long. 79° 44' W, her average speed was 15.2 knots.
Probably the most convincing check came the next morning, September 22. At 0610 hours, in Lat. 31° 46' N, Long. 78° 28' W, the vessel was about 3.5 miles to the right of the axis and maintained that relation to the axis until 1030, in Lat. 32° 24.8' N, Long. 77° 32.5' W. Her average speed in this section was 13.9 knots, or one knot less than had been averaged immediately before when in the axis. At 1158, in Lat. 32° 38.5' N, Long. 77° 15.8' W, the vessel was again in the axis; however, shortly after this the ship’s shaft revolution dropped from 89 RPM to 75 RPM and remained at this speed until 1510. The vessel’s speed during this interval was 13.9 knots. Thus, it would appear that although the shaft speed dropped 14 revolutions per minute the ship’s speed over the ground remained constant.
At 1510 the speed of the tanker increased 89 RPM, and until 2106, Lat. 34° 16.9' N, Long. 75° 34.3' W, the vessel averaged 15.2 knots, or 1.3 knots better at the same RPM than she had 150 miles back when she was out of the Stream’s axis 3.5 miles. The elapsed time between Fowey Rocks and Diamond Shoals Light Vessel on that particular voyage was 45.6 hours.
Comparing the elapsed time of that voyage with six previous voyages for which we have records, shows a reduction of 2.4 hours in running time between Fowey Rocks and Diamond Shoals. To make any further comparison at present would be rather inaccurate, as it is fairly certain that the effect of current in the Stream is greater in the spring and summer. Certainly many more voyages with varied weather conditions must be made in all seasons of the year before any final conclusions can be drawn.
In December, 1949, the Hydrographic Office and the U. S. Coast and Geodetic Survey were informed of results of the investigation to date. Through those agencies a plan has been formulated whereby seven or eight vessels regularly traveling the route in question, and equipped with Loran, will turn into the Hydrographic Office for processing, after each voyage, a log of all Loran fixes, weather and sea conditions, sea temperatures, engine RPM, D. R. speed, and true course. In addition, the above agencies provide overprints on H.O. Chart 0943 and USCGS Chart 1002 of proposed tracks to be followed both north- and south-bound.
Five north-bound tracks and three southbound tracks are provided, with the suggestion that the tracks be followed in sequence so that a particular ship changes its track for each trip. The north-bound tracks range from one on the Gulf Stream’s charted axis itself to others 20 miles off on the right and up to 36 miles off on the left of the axis. The proposed south-bound tracks, all on the inside, are mainly for determining the existence of any eddy or counter-current.
In order to take more accurately into account the varying load conditions of tank vessels, it is suggested also that a standard dead reckoning speed using a standard number of shaft RPM be established by conducting a trial run along course for several hours prior to entry into the Gulf Stream. Doing this establishes a standard dead reckoning speed against a standard RPM and thus makes it possible to compute more accurately the varying speeds of the Gulf Stream between fixes.
Among the objectives of the Hydrographic Office and U.S. Coast and Geodetic Survey in this project is to determine the possible existence of a high velocity section within the Gulf Stream, and if such does exist, to determine its constancy with regard to position and strength. If the axis does meander, the survey hopes to determine, if possible, whether the variations occur monthly, seasonally, or weekly. From such information it might be entirely possible to predict from season to season where the greatest current can be found. Of course, if the variations prove to occur weekly, this sort of service would not be possible. At any rate, the government agencies involved hope to be able to have considerable information concerning the seasonal and possible short period variations of the speed of the Gulf Stream within a year. This depends entirely on how accurately and faithfully the various ships involved follow the instructions.
A group which has done considerable research in connection with the Gulf Stream is the Woods Hole Oceanographic Institution. Their studies have generally been concerned with the Stream north-eastward from Cape Hatteras, partly because more spectacular variations occur along this sector. They have found that the velocity in the swiftest part is generally between 4 and 5 knots. These velocities are usually confined to a relatively narrow band 10 to 15 miles wide and situated on the left-hand edge of the current. However, in this sector, east of Cape Hatteras, the shift of the stream may be 10 miles in a week in either a northerly or southerly direction. These observations show that the highest velocities in the Stream are greater than most previous estimates.
In connection with this high velocity section the Woods Hole group have found strong eddies both north and south of the Stream. These eddies have not been detected by ordinary means of navigation because for each current in one direction there will be an opposite current of nearly equal velocity. It is for this same reason they feel that drift records of ships crossing the Gulf Stream would show less velocity than there actually is. Drift records which were based on infrequent celestial fixes of a ship following the mean course of the Gulf Stream would hardly ever show the maximum velocity of the current. It is evident from their studies that the mean position of the Stream as shown on U.S. Coast and Geodetic Survey or H.O. Charts has little useful meaning in the area to the East of Hatteras. However, due to the confined nature of the current between the Florida Straits and Hatteras, meanderings are undoubtedly at a minimum.
To date, from the limited knowledge we have at hand, it appears that in the sector where the charted axis sweeps to the northeastward (at roughly Latitude 30° to 31° North) a drop of about one knot can be expected. This seems to be evident, regardless of whether on the axis or 3 to 4 miles either side. However, where the charted axis later steadies on a more or less constant heading, an increase in current is felt and a sharper drop encountered as the charted axis is departed. Considerably stronger currents have been recorded all the way to Hatteras than had been previously indicated.
This would indicate that the axis as charted might be considered fairly accurate; however, only time and many observations can substantiate or negate its present position.
(Editor’s Note.—Six United States and Canadian research vessels, manned by more than 350 men, including 50 civilian scientists, sailed on June 6 in “Operation Cabot,” a survey of the Gulf Stream. Vessels participating are the U.S.S. San Pablo and U.S.S. Rehoboth, former U.S. Navy seaplane tenders, now employed by the Hydrographic Office; the H.M.C.S. New Liskeard, operated by the Canadian Naval Research Establishment; the Atlantis and the Caryn, research vessels of the Woods Hole Oceanographic Institute; and the Albatross III, research vessel of the Fish and Wildlife Service of the Department of the Interior.)