Thoughts on Bowditch

I recently acquired a fifth edition published in 1821 of The New American Practical Navigator. After perusing some of its 596 pages, I have been awed by the wealth of precise and valuable information.

Many subjects listed in the Table of Contents of the 1821 edition have long since been removed from more recent editions. But I found these excised sections, such as “Involution of logarithms” or “Finding longitude by the eclipses of Jupiter’s satellites,” thoroughly engrossing.

My eyes caught two interesting sections that I might recommend be returned to the new 1995 edition now being prepared by the Defense Mapping Agency for publication in December of 1994. They are “Surveying” and “Gauging of Wine, Beer and Malt.”

With the pandemonium caused by GPS and the resulting ability to find one’s position more accurately than many charts can portray, it might be well to relearn the aspects of charting as presented here.

Ten finely printed pages are devoted to explaining several techniques of surveying coastlines, bays, inlets, shoals, and banks. These techniques require seamanlike skills that are often hard to find these days: steering a straight compass course, computing set and drift, using a lead line, measuring angles with a sextant, and keeping an accurate log.

An interesting rule is provided for finding distance off an anchored vessel:

“Rule. Multiply the height of the mast above the eye of the observer by 57.3, and the product will be a constant quantity which being divided by the observed angle of elevation expressed in degrees and decimals of a degree, the quotient will be the sought distance nearly.” (57.3° equals one radian.)

Here is an example, using a reprint of plate XI, as a reference; if the height of AB was 30 ft. and the angle ADB was 1°, the distance BD would be 1,719 feet (being 57.3 times as great as AB).

Once the grueling task of surveying was completed, a glass of wine or mug of ale might be appropriate and so the gauging of wine, beer and malt was, in the 1800s, of no less importance than determining noon position. A wine gallon, we are told, consisted of 231 cubic inches and a beer or ale gallon consisted of 282 cubic inches. Lastly, a malt gallon was 268.8 cubic inches.

The New American Practical Navigator even provides an example problem: What is the number of wine gallons contained within a cistern measuring 62″ per side? Answer: 62 x 62 x 62 = 238,328 cubic inches. This is then divided by 231, giving us 1,031.75 wine gallons.

Michael Carr

By Ocean Navigator