Mistake in Bowditch!

[Dockhead]

Originally Posted by StuM

So let's assume a speed of 6 nautical miles per hour.


That's a full mile of line dragged out in 10 minutes which is 1000 knots. Multiply that you 6 and you have 6000 per hour. Something doesn't sound right there..



If you are doing 12 Nm/hr you need 2 miles of line.

Indeed.



AFAIK, in olden days mariners used a special sandglass with the chip log, which ran for usually 30 seconds. The knots were set at 7 or 8 fathoms, not one fathom. Here is what Wiki says about it:


"Initially, the log-line was not knotted and sailors measured the length directly on the line. With the introduction of the nautical mile as a standard unit of measure at sea in the 15th century, they began to mark the line at equal intervals proportional to the nautical mile and to the time interval used for measurement. Initially, the markings were simply knots in the line. Later, sailors worked knotted cords into the log-line. Many ships used knots spaced 8 fathoms (48 feet or 14.6 meters) apart, while other ships used the 7-fathom prescription. The time interval needs to be adjusted according to the distance between knots. Substituting 6,000 feet for 1 mile, the above formula yields 28.8 seconds for a distance of 8 fathoms. In fact, 28-second and 14-second glasses used to be common among navigation equipment."

https://en.wikipedia.org/wiki/Chip_log#Use

[Ambler]

I would say the use of knot or knots in Bowditch's era of sailing, was an attempt at abreviating the "nautical mile". The reason being that writing up the ships log periodically should be as brief and yet concise as possible. The log is a legal document admissible in a court of law, where the two known lengths of a mile (statute and nautical) must be kept unambiguous.

It is to be remembered that the distance of a nautical mile is derived by the circumference of the world via the North and South poles divided by 21,600 (or 360 x 60) or otherwise known as a measure of a minute of arc of latitude.

I don't know how the statute mile is derived but I do know it is very different. But is known more commonly and by the legal fraternity as a mile in length.

Therefore I believe the use of "knots" instead of "nautical miles" was an attempt at keeping the logbook short and yet precise.

[deltaten]

Those old fellas were right smart! Just did the calc and the rate of 8 fath./28 second runs to 5.142 knots or 5.84 mph

[svHyLyte]

Originally Posted by StuM

So let's assume a speed of 6 nautical miles per hour.


That's a full mile of line dragged out in 10 minutes which is 1000 knots. Multiply that you 6 and you have 6000 per hour. Something doesn't sound right there..



If you are doing 12 Nm/hr you need 2 miles of line.

Oops! Stu, you're absolutely correct. My memory is failing (a symptom of aging I guess!) Upon pondering it, I realized the "knots" on our spool were every 10 fathoms--not fathom--and you counted the number that passed over the transom in 1 minute (not 10!). If 10 knots passed, that was one 10th of a mile, roughly (you actually counted the "knots", a little marker on the line, as you wound the spool back in). Sixty minutes x 1/10 mile per minute would yield "6 knots/hour" as you point out.

Coincidentally on the matter, we now use a "KnotStick" to calibrate our paddle wheel knotmeter which seems to prove more accurate for speed through the water than timing runs between known points.

FWIW...

[Dockhead]

Originally Posted by Ambler

I would say the use of knot or knots in Bowditch's era of sailing, was an attempt at abreviating the "nautical mile". The reason being that writing up the ships log periodically should be as brief and yet concise as possible. The log is a legal document admissible in a court of law, where the two known lengths of a mile (statute and nautical) must be kept unambiguous.

It is to be remembered that the distance of a nautical mile is derived by the circumference of the world via the North and South poles divided by 21,600 (or 360 x 60) or otherwise known as a measure of a minute of arc of latitude.

I don't know how the statute mile is derived but I do know it is very different. But is known more commonly and by the legal fraternity as a mile in length.

Therefore I believe the use of "knots" instead of "nautical miles" was an attempt at keeping the logbook short and yet precise.

Have you ever heard anyone ever say, or read anywhere, that "Portsmouth to Cowes is 14 knots?" Or "stand at least 3 knots off the coast?" Or, "The frigate wore ship when she was 4 knots from the Eddystone Lighthouse?"


No, I didn't think so.




The land "mile", if you're interested, comes from the Latin word for "thousand" -- it was a thousand paces.



See: https://en.wikipedia.org/wiki/Mile

[CaptTom]

I was almost ready to believe that someone used to use "nauts" as shorthand for "nautical miles." But of course, Dockhead is right. We'd also hear "nauts" used as a distance measurement if that were true.

And svHyLyte makes a good point that when counting knots (or markers) in a line, if we select the distance between them, and the time, to be equal fractions relative to a nautical mile and an hour, respectively, we'd just count knots over that time to get our actual speed in knots. No math required.

But the result would still be knots per minute, or per ten minutes or per 28 seconds, or per 30 seconds, or whatever time interval may have been used.

Nobody has yet convinced me the chip was left streaming behind the ship for an hour, or that the knots were one nautical mile apart.

It seems to me that's the only way you could justify using the term "knots per hour."

Yes, we're getting pedantic. Still interesting.

[StuM]

Originally Posted by Dockhead

Have you ever heard anyone ever say, or read anywhere, that "Portsmouth to Cowes is 14 knots?" Or "stand at least 3 knots off the coast?" Or, "The frigate wore ship when she was 4 knots from the Eddystone Lighthouse?"

No, I didn't think so.

Rudyard Kipling, "Their Lawful Occasions" (1903)



‘Mr. Hinchcliffe, what’s her extreme economical radius? ‘
‘Three hundred and forty knots, down to swept bunkers.’

[Montanan]

Now it depends on what the context is. A knot could be a tangled mass,

Per wikipedia:

The knot (/nɒt/) is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h (approximately 1.15078 mph)

1 international knot =
1 nautical mile per hour (by definition),
1.852 kilometres per hour (exactly)

The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE); kt is also common, especially in aviation where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.

Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time.

[Dockhead]

Originally Posted by StuM

Rudyard Kipling, "Their Lawful Occasions" (1903)

‘Mr. Hinchcliffe, what’s her extreme economical radius? ‘
‘Three hundred and forty knots, down to swept bunkers.’

An amazing piece of research -- how did you ever find that?


More on the subject:


'Knots an hour'

[mako]

Originally Posted by El Pinguino

How old is the edition? EDIT... just noted ..1926

There was a time when 'knots per hour' was in fairly common usage...

Tracked them down in the one spot here...

https://www.merriam-webster.com/word...-an-hour-wrong

Thanks for the history. I remember reading alot of "knots per hour" in the early Clive Cussler novels (my favorite author). Big faux pas and no excuse in his case.

[Montanan]

Originally Posted by Dockhead

An amazing piece of research -- how did you ever find that?


More on the subject:


'Knots an hour'

Dockhead wonderful reference you linked, best historical description that I have fathomed. Thank you for sharing.

So does anyone know what kind of knots the mariners used in making their chip log? That be the subject of a derivative thread as I am sure there were personal preferences just as there are here on the CF.

Well, I dead reckon that Kipling was using the common phrase and was in good company when saying knots per hour. Heck, why not, its close enough that there wasn't any misconception of what was being referenced. Can't criticize that.

And being an American [Montañan], I all too often hear torque being described in units of foot pounds, which makes as much sense as metre [or meter] newtons. And boy of boy do piston-heads love to brag about and compare the amount of "foot pounds" that their engines yield. Its pound foot! And when there is a plural measurement, the unit is denoted as pounds foot. Yet, I have heard mentioned measurements in units of feet pounds, pounds feet.

Ah. but then let us knot let the subject of this line of thread drift [in the wake] of the conflation of mass and weight of which there has been tonnes written.

Here is to all the two left footed persons. Cheers.

[Dockhead]

Originally Posted by Montanan

. . .So does anyone know what kind of knots the mariners used in making their chip log? . ..

That's actually not so mysterious -- surely a simple overhand knot . . .

[StuM]

Originally Posted by Dockhead

That's actually not so mysterious -- surely a simple overhand knot . . .

One common method was to tie a piece of twine onto the log line. Much easier than tying multiple overhad knots along a very long line and it would mean that the line could be re-purposed if required.


"https://www.lewis-clark.org/article/2795"
"The log-line was divided into equal lengths with knots of twine interwoven with its strands."

[SeanPatrick]

Edited:



It appears from the above pictures that there may have been different numbers of knots in the twine for the various knots. Apparently the piece of cloth before the twine was a "forerunner" - marking the limit of the drift line.