I was a sucker for Long John Silver and voyages to far-away places like the Coral Island but there was a down side to these long journeys in real life because sailors could soon lose track of where they were and many died due to scurvy and lack of fresh water. Unless they knew their speed they could end up miles away from where they thought they were.
Camila Caballero, from the Massachusetts Institute of Technology explains thus:
‘With no landmarks to gauge their progress across the open sea, sailors couldn’t tell how fast or how far they were travelling,’ But when the nautical mile — 1.852 kilometres — was introduced in the 15th century, they had a handy standard against which to measure speed and created out of necessity the log, the world’s first maritime speedometer. ‘They used materials they had on hand, she explains. ‘A wedge-shaped piece of wood, a small glass timer, and a really long rope.’ The rope was knotted at intervals of 47 feet and 3 inches.
‘With no landmarks to gauge their progress across the open sea, sailors couldn’t tell how fast or how far they were travelling,’ But when the nautical mile — 1.852 kilometres — was introduced in the 15th century, they had a handy standard against which to measure speed and created out of necessity the log, the world’s first maritime speedometer. ‘They used materials they had on hand, she explains. ‘A wedge-shaped piece of wood, a small glass timer, and a really long rope.’ The rope was knotted at intervals of 47 feet and 3 inches.
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| measuring a ship's speed |
John Prescott, Cutty Sark volunteer, tells us:
To determine distance, early navigators recorded the ship’s speed regularly, once every half an hour or more. To do this, they dropped a measuring device known as a log into the sea from the stern of the ship. All ships, including Cutty Sark, used a similar method until more advanced mechanical instruments were introduced in the twentieth century.
To determine distance, early navigators recorded the ship’s speed regularly, once every half an hour or more. To do this, they dropped a measuring device known as a log into the sea from the stern of the ship. All ships, including Cutty Sark, used a similar method until more advanced mechanical instruments were introduced in the twentieth century.
The log is made up of a wooden, weighted, triangular drag device that stays stationary in the sea, known as the ‘ship’ or ‘chip’, and a line on a spool that is unwound as the ship sails away from the chip. The officer of the watch, with sandglass in hand, times the log as the line runs out and shouts ‘Belay!’ at a specified interval.
‘Hand the log!’ is then shouted and the sailors start hauling the log in. The line is divided by evenly spaced knots which act as markers. On hearing the order, the seaman watching at the stern checks how many knots in the rope have passed into the sea in the given time, thereby providing a reading of the ship’s speed in knots.
If the speed measured by logline is 9 knots and the wind has stayed constant in strength and direction for the half hour since the log was last streamed to measure the speed, then, as 1 knot is equal to 1 nm/hour, the distance travelled in that time is 4.5 nm.
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| constituent parts of the 'log' |
Speed is equal to distance divided by time. If you know the distance travelled (by measuring the amount of logline that has been dropped into the sea) and the time elapsed (from the officer of the watch’s sandglass), the calculation is relatively easy.
The top recorded speed of Cutty Sark, for instance, was more than 17 knots a speed many power-driven merchant ships today cannot achieve (although remember, Cutty Sark needed a favourable and constant breeze to sail at that speed, such as the Trade winds).
To convert use this: 1 knot = 1.15078 miles per hour
Interestingly the knot is an almost universal term, with identical or similar sounding words in many languages, such as knoten (German), nudo (Spanish) and notto (Japanese).
Interestingly the knot is an almost universal term, with identical or similar sounding words in many languages, such as knoten (German), nudo (Spanish) and notto (Japanese).
I do have a poem that mentions knots.
Au Revoir
(for Julie)
I’ve waited until
the tracker tells me
you’re over Moulin Huet Bay
09.27hrs
278.9 knots
32,520 feet
17,108 kilometres
to go home
but far too cloudy today
to see last Thursday
strolling its Bailiwick heart
down Ruettes Tranquilles
grateful for the shade
you gliding your hand
along moss ridden walls
telling me they’re capillaries
furred with curiosity
slowing us down
down to a Tea Room
that deserves its capital letters
where a tuna salad took you
less time to demolish
than a wave crashing on rocks
from our perfect view
of Renoir’s blues browns greens
and Guernsey’s sparse white clouds
without a single contrail
to break the spell.
First published in the French Literary Review, March 2019
Au Revoir
(for Julie)
I’ve waited until
the tracker tells me
you’re over Moulin Huet Bay
09.27hrs
278.9 knots
32,520 feet
17,108 kilometres
to go home
but far too cloudy today
to see last Thursday
strolling its Bailiwick heart
down Ruettes Tranquilles
grateful for the shade
you gliding your hand
along moss ridden walls
telling me they’re capillaries
furred with curiosity
slowing us down
down to a Tea Room
that deserves its capital letters
where a tuna salad took you
less time to demolish
than a wave crashing on rocks
from our perfect view
of Renoir’s blues browns greens
and Guernsey’s sparse white clouds
without a single contrail
to break the spell.
First published in the French Literary Review, March 2019
Thanks for reading, Terry Q.
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