Transequatorial Routes in the Atlantic

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The best way to sail from one hemisphere to the other has preoccupied mariners ever since early explorers discovered the zone of calms that separates the trade wind systems of the two oceans. 'The well known equatorial embarrassments' is how Alexander George Findlay refers to the doldrums in his Memoir of the Northern Atlantic Ocean published last century, a comprehensive book in which he tries to bring together all that was known at the time about the wind systems of the North Atlantic. The best strategy for tackling the doldrums is discussed in great detail, because fast passages across the equator were still of utmost importance to the masters of sailing ships linking Europe and North America with the rest of the world before the opening of the two great canals and the proliferation of powered vessels.

The first meteorologist who tried to put wind and weather observations on a proper scientific basis was an officer in the US Navy, Captain Matthew Fontaine Maury, who started collecting weather information in a methodical way in the early part of the nineteenth century and originated the pilot charts. Although primarily concerned with the weather of the North Atlantic and the best ways to speed up passages between the United States and Northern Europe, Captain Maury's research also dealt with passages across the equator. The main dilemma faced by ships plying between the two hemispheres was where to cross the doldrum belt. It had been known for a long time that the Atlantic doldrums have a triangular shape with their base lying along the African coast, between the Cape Verdes and the equator, and becoming narrower to the west. Therefore by crossing the doldrums well to the west they may be traversed in a shorter distance.

As a result of Captain Maury's work, based on thousands of observations obtained from the mariners whom he had persuaded to fill in special logbooks provided by him, it was suggested that the equator should be crossed between the meridians of 30 °W and 31 °W. As these recommendations were primarily directed at vessels sailing from North America to either Cape Horn or the Cape of Good Hope, the directions were later modified for transequatorial voyages originating in Europe so as to take full advantage of the seasonal changes of weather which affect the doldrums. Specific directions for each month are necessary not only because of the seasonal movement of the ITCZ but also because the direction of the SE trade winds tends to be more southerly when the sun is north of the equator than when it is south.

Another debate between masters of southbound sailing vessels was the best way to sail around the Cape Verde Islands, whether to westward or between the archipelago and the African coast. Taking up the challenge of Captain Maury's arguments in favour of a westerly crossing of the equator at all times of the year, the Royal Netherlands Meteorological Institute published a comparative study of the routes followed by a number of Dutch sailing ships, both inside and outside of the Cape Verde Islands. The passage times of the 455 Dutch vessels were then compared with the times taken by 144 American vessels, many of them clippers, which had also chosen either the inside or outside route on their voyages across the equator. The results of the combined experience of 599 vessels makes fascinating reading, even if the conclusions are not as clear cut as expected. Many more ships (340 Dutch, 111 American) decided to stay west of the islands than east (114 Dutch, 34 American), but the mean times showed only one day in favour of those that went outside. It does appear that the western track is to be preferred and the only time when the inside passage might be advantageous is between December and February, but the advantage is so small that the final decision as to which route to pursue should be determined by other considerations, which will be discussed in connection with the relevant routes.

The controversies caused by the Atlantic dol drums continue to this day and the dilemma has still to be resolved. The optimum strategy for southbound transequatorial routes is a major consideration for the skippers and navigators of the various round the world races, who rack their brains over which route will give them the best run to either the Cape of Good Hope or the Horn just as the masters of yesterday's clippers did before them. However, with ever improving satellite observations, the doldrums might finally give up their secrets and land based weather routeing services can now advise even small sailing boats on • the best way to go. Much of the fun and excitement will be taken out of route planning, but at least those 'equatorial embarrassments' will cease to be a nuisance.

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