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The great thing about the English system of measure versus the SI (or metric) system is that there are so many ways of measuring things. On this page, we provide definitions of some of the common and uncommon measures used onboard.

Commonly Used Units of Measure

A measurement of length equal to 6 feet. Often used to describe depth. "In running along shore we shoald in our water from 9 to 7 fathom and at one time had but 6 fathoms which determined me to anchor for the night." -- The Endeavor Journal of James Cook 22 May 1770.

A measure of speed equal to one nautical mile per hour. It is considered by many to be incorrect usage to say, "knots per hour." Derived from original measuring device in which a piece of wood was attached to a line with knots tied at regular intervals. When the wood was tossed overboard, the number of knots passing in a given period of time recorded the speed. "Having for some time past generally found the Ship by Obsern to the Northward of the Logg, which is not owing to a current as I at first imagined but to a wrong division of the Log line being 2 1/2 feet in each knot; but this is now rectified." -- The Endeavor Journal of James Cook 12 February 1769.

Nautical Mile
A measure of length based on one minute of latitude. Since latitude varies with longitude (the earth isn't a perfect sphere), the International Hydrographic Organization adopted 1852 meters or 6076.12 feet as the international nautical mile.

Less Commonly Used Units of Measure

A measure of length equal to one tenth of a nautical mile. Approximately, 100 fathoms. "At 9 oClock being little wind and variable we were carried by the Tide or current within 2 Cable lengths of the NW shore where we had 54 fathoms water, but with the help of our Boats we got her Clear." -- The Endeavor Journal of James Cook 15 January 1770.

Loops of rope. Small stuff (thin diameter line) is often sold by the hank. Actual length is variable, lengths of 50 or 100 feet are common. Fore and Aft sails were originally tied to stays using small pieces of line, hence the expression "hanking on a sail." For those who avoid roller furling jibs, the pieces of hardware used to attach the jib to the forestay are called hanks.

At sea, a measurement of length equal to 3 nautical miles. (Also called a nautical league.) "At day light in the Morning we made sail Cape Manifold bearing South-by-East distant 8 Leagues" -- The Endeavor Journal of James Cook 28 May 1770.

A measurement of length equal to 15 fathoms (90 feet) in the U.S. and 12.5 fathoms (75 feet) in Great Britain. Almost always refers to a measurement of chain.

A measurement of length equal to about nine inches. Taken from the distance between the tip of the thumb and the tip of the little finger in a fully extended hand.