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http://home.tiscalinet.be/koweymeis/converter/extra/units.htm has this:

  shackle -
    unit of length used at sea for measuring cable or chain
    1 shackle = 15 fathoms (90 ft/27 m)

A great web page about units (although it is silent about the shackle) is:

http://members.aol.com/JackProot/met/spvolas.html

Here is an excerpt:

---

"Nautical" units :

1 fathom = 6 feet = 2 yards (= 1.8288 m) - widespread use (see Antiquity)
1 cable length = 120 fathoms = 720 feet (= 219.456 m) - - - See below
1 nautical mile (Brit.) = 6080 feet (= 1853.184 m) - - - See below
1 nautical mile (Int.) = 1852 m exactly (= 6076.115 Int. feet)
(and 3 nautical miles = 1 nautical league -- 3 * 1852 = 5556 m)
Note : 1 knot = 1 nautical mile/hr (speed unit)

You may encounter a Mark Twain in the US : equals 2 fathoms or the minimum
safe clearance for steam wheelers (came before the writer and inspired his
pen name)

Never heard of a cannon shot ? This was about 3 miles in the last century,
and explains why the US territorial waters were set at this distance
originally.

Notes : the Nautical Mile is defined as the length of 1 minute of arc along
a meridian, but the Earth is not a perfect sphere. Therefore 1 minute will
be equal to 6046 feet at the Equator and 6108 feet at the Pole. The average
is 6077 feet, which was rounded off to 6080 feet by the British Admiralty.

In 1929, the International Nautical Mile was defined as 1852 meters exactly
(which brings us closer to the original average.) The United States adopted
it in 1954.
There is also a Geographical Mile defined as 1 minute of arc along the
Equator and equal to 6087.2 feet - or 1855.378 meters.

About cable length, I received an E-mail from Ralph Zimmermann stating :
"You list a cable as being 720 feet, which is accurate if you are talking
about depth in water. A cable refering to a distance across water is defined
as 1/10th of a Nautical Mile". I rushed to my old Encyclopaedia Britannica
and it confirmed : "the old usage whereby the length of a hempen anchor
cable was 101 fathoms survives in the British naval measurement of a 'cable
length' or one-tenth of a nautical mile".

---

And also on that page, for Russell:

  "In South Africa, the Cape foot was 0.314858 meter -- used until 1950"

Dan

-----Original Message-----
From  Navigation Mailing List
[mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Russell Sher
Sent: Thursday, July 12, 2001 11:07 PM
To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
Subject: Cable units


Does anyone kow what is the length of a shackle as a unit of length? One
shipping operator  referred to the anchor chain length's in shackles.
Russell

   

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