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
Fathom
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.
Knot
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
Cable
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.
Hank
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.
League
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.
Shot
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.
Span
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.