Just one hundred years ago the National Observatory (the forerunner of both the Naval Observatory and the Hydrographic Office) issued its first Track Charts for the North Atlantic. Prepared for the information and use of sailing vessels, the charts contained principles that were rediscovered nearly a century later and applied to aircraft navigation. These charts were the work of Lieutenant Matthew Fontaine Maury, U. S. Navy, who had perceived the need for information of their type when serving as master of the sloop-of-war Falmouth on the South Atlantic station in 1831. In making preparations for sea, he had been impressed by the fact that there was no available information or chart showing what winds and currents to expect along his course. Assigned to the Depot of Charts and Instruments as Superintendent in 1842 after breaking his right leg, Maury forthwith made the compilation of data from sea observations one of his major fields of study. He realized that the daily entries in ship’s logbooks of wind forces and directions, courses made good, and “remarkable occurrences” represented an undeveloped major source of information on oceanography and marine meterology.
There existed a collection of log books of United States men-of-war, gathering dust in the files of the Navy Department; but most of them pertained to voyages to South America or the Mediterranean, whereas the routes then of chief interest to American commerce were those to North Europe and China. A circular letter was therefore addressed by the Chief of the Bureau of Ordnance and Hydrography in 1842 to American shipmasters, requesting them to furnish Maury’s office with any information pertaining to navigation that they might collect. The response to this request was disheartening: not a single reply was received from the Merchant Marine until 1851. A less persevering character than Maury might have been discouraged; but he quietly went to work on the Naval logs. He also read papers on the subject before the National Institute and the Association of American Geologists and Naturalists, using the prestige of these societies to induce the Navy Department to issue instructions for the keeping of better logs.
Good data were now coming in from the fleet, and Maury’s staff at the Depot (which he preferred to call the National Observatory) completed in 1847 the tabulations for three sheets showing conditions encountered in the North Atlantic on the track to the Equator. Laid down on a large scale—ten degrees of latitude covered eight inches—these charts were nevertheless cluttered with data, as they contained not only the course lines of the vessels whose logbooks had been analyzed, but also symbols for wind and weather, and set and drift of currents, distinguished as to seasons.
Despite the intricate character of the charts, it was clear to Maury that they pointed to a more direct route between New York and the Equator than the one commonly in use. Ships bound to California, China, or South America at this time all followed the same route as far as the Line: they bore well out into the North Atlantic, then headed for the vicinity of the Cape Verde Islands, and finally steered southerly to cross the Equator near 20° W longitude. From there they stood for the Brazilian coast below its westerly bulge (Cape San Roque), so that two virtually complete crossings of the Atlantic were accomplished in making good the difference of latitude between New York and Rio de Janeiro. According to Maury’s charts, there was ample wind to hold practically a great circle course from New York to an Equatorial crossing in the vicinity of 30° W longitude, and he lost no time in drawing attention to this finding.
The first test was given by Captain Jackson of the Baltimore bark W.H.D.C. Wright. Bound to Rio with a cargo of flour from the Chesapeake Bay, he crossed the Line in 31° W, 24 days out, and arrived at Rio in February 1848, 38 days from the Virginia Capes. The average passage at this period was about 55 days. Jackson returned in 37 days, the round trip, including 10 days detention at Rio, taking only 85 days.
Public recognition of the value of Maury’s work was now quick and enthusiastic. Thousands of ships began keeping meteorological logs, in return for which their captains received a set of Maury’s charts, with an accompanying volume of Sailing Directions. New charts, analyzing these logbooks, poured out of Maury’s office: Trade Wind Charts, showing the seasonal fluctuations of the trade winds; Pilot Charts, with wind roses for the seasons for each 5° quadrangle of latitude and longitude; Thermal Charts, showing the distribution of sea surface temperature; Storm and Rain Charts; and Whale Charts, showing the location of the whaling grounds. In 1853, following an International Conference in Belgium which led to formation of the present International Meteorological Organization, all the war and merchant ships of the civilized world were keeping meteorological abstract logs.
Month after month, new record passages were reported by ships using Maury’s charts. In January, 1853, the Phantom sailed from New York to a point off Rio de Janeiro in only 23 days. The Grey Eagle made the return trip, from Rio to Philadelphia, in 23 days in May and June, 1852. The run from New York to San Francisco, which took 160 to 180 days in 1847, was made in 1851 by the ship Flying Cloud in 89 days and 21 hours, and the same ship shaved 13 hours off that time three years later. The Northern Light made the homeward voyage, San Francisco to Boston in 76 days, 6 hours, in 1853. Similar records were set on the routes to China, Australia, and the Hawaiian Islands. Admittedly, much of the improvement was due to the introduction of clipper models and the encouragement toward faster ships given by the discovery of gold in California and Australia; but the presentation to Maury of a set of plate and a purse of $5,000 in 1853 by the hard-headed business men of New York City is good evidence of the value placed on his work.
Publication of Maury’s charts and Sailing Directions stopped in 1861, when he joined the Confederate Navy. The keeping of meteorological logs by American vessels was also suspended. In the 1870’s the Hydrographic Office commenced the analysis of a new series of logs which led to the production of the familiar monthly Pilot Charts. The first of these was the December, 1883, Pilot Chart of the North Atlantic. The earliest numbers had only wind roses, leaving the shipmaster to pick his own route, but on the chart for May, 1884, were laid down Maury’s old sailing ship routes across the Atlantic and to the Equator. Other routes were added shortly, and by October, 1885, the chart contained nearly all the information shown at the present time.
In response to a resolution of the San Francisco Chamber of Commerce, the first monthly Pilot Chart of the North Pacific was issued in January, 1894, while the quarterly charts of the South Atlantic, South Pacific, and Indian Ocean first appeared in 1909. The Central American Waters chart introduced in 1915 completes the series. Each chart carries the statement “founded upon the researches made in the early part of the nineteenth century by Matthew Fontaine Maury while serving as a lieutenant in the United States Navy,” and while the sailing ship routes are now of little concern to the Merchant Marine or Navy, they are retained partly out of sentiment (since they are the only features of the chart actually derived from Maury’s own work) and partly for the benefit of yachts, which still cruise under sail to the far corners of the earth.
How did Maury arrive at these sailing routes? First he took the log book records and tabulated the force and frequency of occurrence of the wind from each alternate point of the compass, for each 5° quadrangle of latitude and longitude, for each month. Then, knowing how a sailing vessel performed with the wind at various relative bearings (see Table 1), he laid down the route from quadrangle to quadrangle that the ship, under the average wind conditions, could cover in the shortest time. The critical portions of these routes are near the Equator, where one set of trade winds gives way to the other, and Maury prepared very explicit directions as to the longitude in which the Equator should be crossed for each month of the year. Likewise the monsoons off the African coast and in the Indian Ocean and China Sea called for careful treatment.
We now know one thing about the wind that had not been discovered in Maury’s day. This is the fact that the direction and force of the wind can be deduced from the distribution of atmospheric pressure, and that, putting matters very simply, the direction of the wind will be roughly parallel to the isobars on a weather map, and the force will depend on the pressure gradient, or the spacing between isobars. In the Northern Hemisphere the wind is clockwise about a “high” and counter-clockwise about a “low,” while in the Southern Hemisphere, the opposite is true.
Figures 1 and 2 are simplified versions of the Pilot Charts in which the wind roses, representing average winds for the months indicated, have been replaced by isobars, showing the average pressure distribution at sea level for the month. Arrow points have been added to show the corresponding wind directions resulting, while the wind force is greater in regions where the isobars are more closely spaced. Also shown on the figures are Maury’s recommended sailing routes between various ports.
One of the important features of the sailing routes is readily apparent, namely, that the outward routes and the homeward routes are quite different; and the isobars show the reason for this very well. For example, the October route from San Francisco to Seattle on Figure 1 requires the ship first to head several hundred miles offshore before trying to make northing; while the return trip is as direct as the configuration of the shoreline allows. The reason for this is the high-pressure zone that lies off the Pacific Coast during this season, so that the prevailing wind along the coast is from the northwest. The route from San Francisco to the Bering Sea likewise finds a head wind, so that a ship must stand well to the westward before heading north, while the return trip is a rhumb line with a fair wind all the way. The route from San Francisco to Hawaii, on the other hand, is a direct one at this season, but on the return trip a sailing ship must head north to the latitude of San Francisco before turning east, and thus sail half again as far, in order to evade the unfavorable wind pattern set up by this same North Pacific High. Similarly, the recommended track from San Francisco to Callao, Peru, after crossing the Equator in 110° W, required a great, counter-clockwise sweep, to approach Callao from the southwest out of the High near Easter Island.
Maury’s sailing ship routes, depending as they do on the distribution of atmospheric pressure, have a close resemblance to “Pressure-pattern Flying” as developed in the last few years for trans-oceanic aviation. (See Pressure Pattern Flight, Office of Research and Inventions, September, 1945.) The first and obvious difference between the two systems is that the Maury method makes use of the climatological average of pressure distribution, while the aviation method, recognizing that the average picture is usually obscured by the effects of the “highs” and “lows” travelling in a generally easterly direction, uses the isobars from the current weather map.
Table 1 | ||||
Speed of a Sailing Vessel in Knows for Winds of Various Force and Direction | ||||
Relative Bearing from Bow | ||||
Force, Beaufort | 15-17 points (Before the wind) | 9-15 points (Wind on quarter) | 6-9 points (Wind abeam) | 5-6 points (Close hauled) |
1 | 1.9 | 1.9 | 1.8 | 1.5 |
2 | 2.9 | 3.0 | 2.9 | 2.4 |
3 | 4.4 | 4.8 | 4.8 | 3.9 |
4 | 5.6 | 6.2 | 6.4 | 5.3 |
5 | 6.9 | 7.5 | 7.7 | 6.1 |
6 | 8.2 | 8.8 | 8.5 | 6.6 |
7 | 8.8 | 9.1 | 8.7 | 6.7 |
8 | 9.3 | 9.5 | 8.5 | 5.0 |
9 | 9.4 | 9.5 | 7.3 | -- |
10 | 9.1 | 8.8 | -- | -- |
11 | (speeds dependent on sea conditions) | -- |
(Data from Capt. M. Prager “Die Fahrtge-schwindigkeit der Segelschiffe auf groszen Reisen” Ann. Hydrographie 33: 1-17, 1905. Average for wooden full-rigged ships, median tonnage 1315, corresponding to the larger ships of Maury’s day.)
The other difference between the two cases lies in the fact that a sailing vessel derives all its propulsion from the wind, and can make use of any wind direction more than five points from the direction in which it wishes to go. Table 1 shows that even with wind abeam, a sailing vessel develops about 90% of the speed it makes under the most favorable condition, and actually sails a little faster with the wind a few points on the quarter than with it directly astern. Table 2 shows the relationship between the wind speed and speed of a sailing vessel. Aircraft, on the other hand, are propelled by their own power at speeds three to ten times that of the wind; but, being totally immersed in air, they can benefit only by the component of the wind in the direction of their course, while any wind forward of abeam is a manifest hindrance.
For this second reason, the sailing vessel tracks can cut close to the center of a “high” or “low,” while aircraft courses are generally laid well beyond the center or “eye,” in order to derive as much benefit as possible from the favorable winds. Thus, in Figure 2, the dotted course from New York to the Equator shows the traditional sailing vessel route, going well beyond the center of the mid-Atlantic High with sails full all the way, while Maury’s route, the one on which the W.II.D.C. Wright set her record, although requiring a ship to do more sailing “on the wind” was so close to the great circle course that the saving in distance more than compensated for the slight reduction in speed.
Table 2 | |||||
Sail Carried and Ratio of Ship Speed to Wind Speed | |||||
Force, Beaufort | Wind speed, knots (mean) | Wind on quarter | Close hauled | ||
Sail carried | Speed ratio | Sail carried | Speed ratio | ||
1 | 2 | All plain sail and studding sails. | .95 | All plain sail and stay-sails. | .75 |
2 | 5 | ditto. | .60 | ditto. | .48 |
3 | 8 ½ | ditto. | .56 | ditto | .46 |
4 | 13 ½ | ditto. | .46 | ditto. | .39 |
5 | 19 | ditto. | .39 | All sail except royals. | .32 |
6 | 24 | All sail except royals and topgallant studdingsails. | .37 | Topgallant sails over single-reefed topsails. | .28 |
7 | 30 | Courses, single-reefed top-sails, topgallant sails. | .30 | Courses, double-reefed top-sails, fore topmast staysail. | .22 |
8 | 37 | Single-reefed courses, double-reefed fore and main top-sails, close-reefed mizzen topsail. | .27 | Single-reefed courses, treble-reefed fore and main top-sails, close-reefed mizzen topsail, fore topmast stay-sail. | .14 |
9 | 44 | Close-reefed courses, close-reefed fore and main topsails, fore storm staysail. | .22 | Close-reefed courses, close-reefed fore and main top-sails, storm staysail. | -- |
10 | 52 | Close-reefed foresail, close-reefed main topsail, fore storm staysail. | .17 | Close-reefed foresail, close-reefed main topsail, storm staysail. | -- |
11 | 60 | ditto. | -- | ditto, or storm sails. | -- |
12 | Over 65 | Scudding under bare poles. | -- | None: lying to, drifting bodily to leeward. | -- |
(Data from Bowdilch, 1888; Bowditch, 1938; and Table 1.)
Students of Maury’s life are invariably impressed by his approach to the scientific problems of his time, for his point of view would be considered “modern” today, and there is no better example of this than the use by present-day aircraft of principles discovered by him more or less empirically a hundred years ago.
A graduate of the University of California, Lieutenant Commander Lyman did research work at the Scripps Institution of Oceanography. He then served for over five years in the Navy: in the Bureau of Ordnance; at the Naval Proving Ground, Dahlgren, Virginia; with the Naval Technical Mission to Japan; and finally as an oceanographic observer at the Bikini atom bomb tests. At present he is in the Division of Oceanography, Hydrographic Office, preparing the scientific reports on the Navy’s “Highjump” Antarctic Expedition.