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Old 05-08-2014, 01:26   #1
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How Long is a Cable, Really?

Cable? Do you know how long it is? Maybe how many football fields equal one cable? Did you know that different countries define a cable in different lengths?

What do you think of a currently published sailing guide that uses cables to describe the distance between point A and point B, rather than meters or nautical miles?

Bill
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Old 05-08-2014, 01:32   #2
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Re: How long is a cable, really?

A modern cable is one tenth of a nautical mile, so 185.2 meters or thereabouts. ie 0.2' is 2 cables. We used it all the time on ships, with it being much easier and clearer to say 2 cables rather than point two miles.
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Old 05-08-2014, 01:35   #3
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Re: How long is a cable, really?

Wikipedia:

A cable length or cable's length is a nautical unit of measure equal to one tenth of a nautical mile or approximately 100 fathoms. The unit is named after the length of a ship's anchor cable in the age of sail. The definition varies:

International: 1⁄10 nautical mile, or 185.2 m
Imperial (Admiralty): 1⁄10 Admiralty mile, or 608 ft (185.32 m), about 101 fathoms
The traditional British fathom varied from 5 feet to 7 feet in the Merchant Navy.
U.S. customary (US Navy): 120 fathoms (720 feet, 219.456 m)



Fathom
fathom (abbreviation: ftm) = 6 feet or 1.8288 metres, is a unit of length in the old imperial and the U.S. customary systems, used especially for measuring the depth of water.

There are two yards (6 feet) in an imperial fathom.[1] Originally based on the distance between a man's outstretched arms, the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around 5–5 1⁄2 feet (1.5–1.7 m).

1 fathom =
SI units
1.82880 m 182.880 cm
US customary / Imperial units
6.00000 ft 72.0000 in

As you can see, the problems stem from
1- The difference between US and Imperial measurements
2- International Standards (IS) and US and Imperial measurements.

The same errors occur when discussing f.eks. gallons the imperial gallon is not the same as the US gallons.

A cables length is frequently used as a measurement in the UK, as is Fathom. So depending on the audience, it is natural this is used.

Just to add to the confusion:

What about Beaufort/Knots/meters per second for wind speeds? (rough conversions: 2 x beaufort = meters per second X 2 = knots

Of course, not to mention the metric system versus yards/feet/inches
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Old 05-08-2014, 04:45   #4
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Re: How Long is a Cable, Really?

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Originally Posted by svBeBe View Post
What do you think of a currently published sailing guide that uses cables to describe the distance between point A and point B, rather than meters or nautical miles?
Guess it depends on context and distances, if they are saying 12 cables I would be pretty disappointed. Better to say 1.2 Nm cables are only really used for distances under a nautical mile.

Bit I think its probably better just to write 0.2 nm instead of two cables as in a written format we normally would write it like this onboard, its more consistant overall, and thats how our instruments read. That is unless we have one of those stupid plotters that want to convert small distances into meters or feet.

So on the whole yes, I think you have a point.
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Old 05-08-2014, 05:11   #5
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Re: How Long is a Cable, Really?

For me a cable measurement is primarily used for discussing close proximity radar work

Used to measure and log CPAs whether passing abeam land points , close traffic or to denote safety zones at anchorage.

However I insist 3 cables are officially logged as 0.3nm

The fact that it is an easy measure on charts or the fixed ring radar display just simplifies communication with the watchkeeper when you are called to the bridge in the middle of the night.
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Old 05-08-2014, 06:10   #6
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Re: How Long is a Cable, Really?

1/10 of a mile.

I only use meters/feet (we are metric) when less than a cable of distance, and for depths.

b.
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Old 02-10-2014, 04:55   #7
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Re: How Long is a Cable, Really?

Quote:
Originally Posted by svBeBe View Post
Cable? Do you know how long it is? Maybe how many football fields equal one cable? Did you know that different countries define a cable in different lengths?

What do you think of a currently published sailing guide that uses cables to describe the distance between point A and point B, rather than meters or nautical miles?

Bill

I think what Bill is referring to is the Adriatic Pilot guide published by Imray. We have guides from all over and never saw the mesurement of cable before and had to look on line to figure it out. But as we are sailing along we have to convert cables to feet to nm and that just does not work.

Imray really needs to either stop publishing that guide or put out an entirely new one. We got 777 in Croatia after finding the Imray guide terribly out of date and sometimes just wrong. We tried to find a 777 guide for the Eastern Italian coast but could not find and again we found the Adriatic Pilot guide very out of date, incompete and the author did not take the time to update charts when he even says their are shoals but fails to show them on the charts like Imray does in their other guides.
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Old 02-10-2014, 05:03   #8
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Re: How Long is a Cable, Really?

> But as we are sailing along we have to convert cables to feet to nm and that just does not work.

No, just move the decimal point one place (divide by 10) and you have NM. No need to involve feet.

(For anything less than a cable, 20 metres is a good approximation to .01 NM)
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Old 02-10-2014, 05:05   #9
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Re: How Long is a Cable, Really?

Double post removed - the forum hiccuped when I posted.
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Old 02-10-2014, 05:57   #10
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Re: How Long is a Cable, Really?

I almost always find the length of a cable to be 6" to 3 feet short of the desired termination.... Heavily dependent on the cost and availability of said cable... AND most importantly... the effort required to install the run... The undisputed king being mast run radar...
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Old 02-10-2014, 14:42   #11
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Re: How Long is a Cable, Really?

And, to the second part of BeBe's question, what do I think of the cruising guide that uses cables (to describe shorter distances than a mile). The first time it really threw me off! I hadn't realized how small a cable is! Since then, it is a real warning relative to small harbors of refuge.

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Old 02-10-2014, 14:59   #12
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Re: How Long is a Cable, Really?

Why are US and UK definitions of cable length different?


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Old 02-10-2014, 15:52   #13
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Re: How Long is a Cable, Really?

The Canadian Coast Guard uses "cable" in its broadcasts. Perhaps as a homage to Stan Rogers' "Barrett's Privateers."
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