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Nathaniel Bowditch The Practical Navigator
Salem’s irascible little “arithmetic sailor” made seamanship a science and left all mariners in his debt
August 1960 | Volume 11, Issue 5
At this period, the start of the nineteenth century, Salem was engaged in a deadly struggle with Boston to become the queen city of American shipping. The Far East—the Philippines, the Indies, the whole vast Orient—was the prize, richer than any man’s imagination could conceive. Daily the ships sailed down the channel from Salem harbor, reaching farther and farther, to return one, sometimes two, sometimes three years later, deeply laden and fat with profits that in a single voyage might run as high as seven hundred per cent. The little New England town was rich in spices, silks, rare goods from the whole world. It rang at night to the boisterous shouts of celebrating seamen. The great shipowners—Elias Derby, the Crowninshield family, and others—exercised a feudal lordship over the whole village and its people.
Old Elias Derby—the same who owned the Henry —conceived a bold plan. The route of the Boston ships to the Orient was south to Cape Horn, then north and west across the Pacific. Salem ships took to the east across the Atlantic, doubled the Cape of Good Hope, and then headed north and east again into the Indies. Derby decided that he would send a ship where no ship from Salem following this route had ever gone before—clear to Manila, the fabled pearl, the trading post of the whole Orient.
He owned a big vessel called the Astrea —too large and slow for the normal trade routes, but perhaps just the thing for the long and difficult voyage to the Philippines. Derby poured money into her outfitting. Unusually heavy and lofty masts, stout rigging, spars, sails—everything was added to make the Astrea fit for the dangerous trip.
As captain, Derby selected Henry Prince, possibly because of the very fast and profitable voyage Prince had just turned in on the Henry . In any case, Derby knew that in Prince he had an exceptionally fine seaman who could be trusted to drive a ship to the very limits of her capacity and at the same time keep a sharp eye on those all-important profits.
Now, no matter what explanation Derby or anyone else might have had for the Henry ’s fast voyage, Prince knew that she had been navigated . Accordingly, he convinced Derby that Bowditch should go along on the trip to Manila, and the little mathematician was signed as supercargo. The Astrea cleared Salem on a stormy day in March, 1796.
The first leg of the voyage took them to Lisbon for water and a cargo of wine, then south for the long reach to the tip of Africa, then north to the isle of Bourbon, a last water stop for Salem ships outbound to the Indies.
With the aid of a favorable monsoon—and Bowditch’s navigation, no doubt—the ship worked her way across the Indian Ocean, through the islands, into the China Sea, and thence to Manila. By the time she had disposed of her cargo and reloaded, the monsoon wind, which shifts direction twice yearly, had changed, and was now blowing from the north. With this fair wind behind her, the Astrea cleared Manila for Salem again and after an uneventful trip arrived safely in May, 1797, having been gone about fourteen months.
During this first voyage of the Astrea to Manila, Bowditch found time to improve and simplify his method of determining longitude until he was fully satisfied that it was reliable. The problem of these lunar sights solved, one further block remained, and it was perhaps the more vexing.
The mathematics of navigation (really applied astronomy)—calculus and spherical trigonometry—were beyond the abilities of most mariners. In addition, they took much too long. If a fix were to be of any practical value to a ship, it would have to be simply and accurately made and it would have to be available soon after the sights had been taken. In spite of his impatience with minds less gifted than his own, Bowditch was fully aware of these problems. How could involved mathematical concepts be made easy?
Attempts had already been made—notably by the famous English mathematician, John Hamilton Moore—to deal with the difficulty by formulating tables for each possible reading of the altitudes above the horizon of the various navigators’ stars. This set of figures was then applied to the problem of the moment, and by means of simple formulas, plus plain addition and subtraction, the fix could be made. Once these tables were assembled, the correct solution to any problem in navigation would be available to any seaman, no matter how unlettered, as long as he could read a sextant properly and remember his sums.
In the period after the first voyage of the Astrea , Bowditch made the acquaintance of an enterprising young man named Edmund M. Blunt. Blunt was a Newburyport book publisher who had pirated and printed in America a set of Moore’s tables, which he called Moore’s Navigator . Though this book was the best thing available at the time, it was rudimentary, and from it no small part of the sailor’s mistrust for mathematical seamanship was derived.