In your intro to navigation you’ll be shown charts that display soundings in feet, fathoms, and meters. These units are entirely arbitrary, generated not by science but by history, the details of which are often murky. Ancient units were often, naturally enough, generated from human body parts: a foot (now standardized to 12 inches), a step or pace (which became the yard, 36 inches), a hand (4 inches), and a fathom (6 feet), which was originally the outstretched arms of a man. The meter is ever-so-slightly more scientifically based (don’t trouble yourself with that link) and is part of the International System of Units, abbreviated SI, the most commonly used system worldwide but not here. In America, we consider it our patriotic duty to avoid being like everyone else. This makes communicating with others a bother, which it should be. We also have red, right, returning although much of the world uses green, right, returning. We pity them.
Nautical history, being long and multicultural, is a mish mash of all kinds of terms and units of measure like “chains” (66 feet) and “shots” (roughly an ounce unless you’re friends with the bartender) or “shot of chain” (90 feet or 15 fathoms) which is a different unit from chains or shots. A shot is usually the same as a “shackle” but I wouldn’t count on it. The “chain” is more of a lubberly term; one-quarter of a chain is a rod, and 80 chains is a furlong. But what you sailors want is a “cable” (I wouldn’t read that either) which is 120 fathoms or 720 feet American although the French, with their hoity-toity SI system, say it is 200 meters which works out to about, although not exactly, 109 fathoms.
The fathom, as far as I know, is always used for depth. (Don’t go into the Home Depot and try to order five square fathoms of carpeting. Or actually, go ahead, give it a try.) Thus we have the phrase, to “deep six” something, based on the tradition of burials at sea, which require the body to be lowered to at least six fathoms. Still, in clear water, this would not obscure the remains of the departed.
So, to summarize, as a practical example we can give the following. Once I sailed through the Corinth Canal. The canal is 28 stadia or 23 cables or 256 chains or 9/10 of a league or 2816 orguia, if it’s easier for you to think in those, or 16,896 feet or 1,024 rods or 25.6 furlongs or 9,300 cubits (in biblical cubits; but of course in classical Greece, it would have been 11,140 cubits, due to inflation), 3.202168898848118 statute miles, or for us sailors, 2.7826086956521739 nautical miles long.
I hope this clarifies things.
Is there a salty term that you’d like to know the meaning or origin of? Many of of the terms and sayings that we use in every day life have nautical origins. Send us your questions and we’ll pass them on to Tony for thorough research and explanation!