mckenzie.keith
Aspiring Anarchist
Yes, one sailor in the crow's nest, another casting leads. Also watching out for land birds, etc.
Astrolabe Anarchy!
- Thread starter Jud - s/v Sputnik
- Start date
2airishuman
The Loyal Opposition
It depends. The best mechanical wristwatches sold today are accurate +/- 2 seconds per day; good marine chronometers (Hamilton etc) are (with rating) accurate within 2 seconds per month. FWIW I have a HAQ watch that I wear every day that is accurate within about 1 second per month if it is constantly worn so that the temperature is relatively constant. The battery is 3 years old and should be good for one more year before it has to be replaced. It was not particularly expensive, a few hundred dollars.
Basic periodic service on a Hamilton Chronometer is, iirc, around $1000, assuming there's nothing actually wrong with it.
At +/- 2 seconds a day on a 10 day passage to, say, Bermuda you would be within 20 miles which is probably good enough for most purposes.
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El Borracho
Barkeeper’s Friend
So the navigator will need to sail well E or W then run down a latitude. On a clear day, too.
Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #145
Newsflash - just picked up my second sextant, a brand new, unused Davis Mark 25 for only $25. It’ll be my practice instrument - and actual one to supplement my better metal one.
Meanwhile, a little video about the results of Sir Cloudesley Shovell’s disastrous collision with the Scilly Islands, resulting in the death of 1400 seamen, one of the greatest British maritime disasters.
A bit old but still worth a watch (and see book of the same name, I think):
Meanwhile, a little video about the results of Sir Cloudesley Shovell’s disastrous collision with the Scilly Islands, resulting in the death of 1400 seamen, one of the greatest British maritime disasters.
A bit old but still worth a watch (and see book of the same name, I think):
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Diarmuid
Super Anarchist
Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #147
Coming into Honolulu can be slightly heart-in-mouth if you’re not paying attention to the buoys and watching the breakers and surfers from seaward...
Hopefully you’ve seen this from much farther away and put down the sextant long before that...
Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #148
Finally a chance to post a good article about - yes, astrolabes. (With a basic short video by the curator of Islamic objects at the British Museum explaining how they work and a bit of their history.) Lots of details about these remarkable devices - hard to imagine how important and sophisticated these things were!
The astrolabe: the Swiss Army knife of ancient celestial navigation
I actually had no real idea about them when I started this thread - just that they were old, pre-sextant navigational devices. I just wanted to start a thread on “traditional navigation” in general, because it’s interesting. Most people are rather boring and like to push buttons and swipe screens, because that’s what they know, being generally unaware of other “ways of knowing”. The astrolabe was truly a multi-functional tool in the hands of a knowledgeable person - from figuring out Islamic prayer times, the direction to Mecca, identifying stars, determine the height of the sun, finding latitude, when to plant crops or collect taxes, even seeking astrological information/advice, when that sort of thing was seen as very important. Etc. Etc. A sort of computer of its day?
“The inventor of this remarkable astronomical device has been lost to history, although some scholars credit Hipparchus, an ancient Greek astronomer and mathematician, with the invention of the disk-like tool, based on evidence from 160 B.C. that suggests he determined the precession of equinoxes in Rhodes. However, the astrolabe began to be widely used during the height of the Roman Empire, sometime between the 2nd and 4th century A.D.
”In ancient times, the astrolabe was mainly used to tell the time, and not necessarily for navigation. This changed when the instrument was heavily modified and refined in the 9th century by scientists from the Islamic world.
”Astrolabe technology changed hands, spreading from the Islamic world to Europe through North Africa and Spain in the 11th century. By the 13th century, European usage of the astrolabe was widespread.
“It stayed in use for centuries by European and Islamic cultures up until the 18th century when it was replaced by more sophisticated technology.”
For “modern” navigation, apparently you had various ‘plates’, each etched with lines indicating star directions, etc., depending on what latitude you were at - so, navigators used a different plate for navigating the Mediterranean than for around the southern tip of South America.
The astrolabe: the Swiss Army knife of ancient celestial navigation
I actually had no real idea about them when I started this thread - just that they were old, pre-sextant navigational devices. I just wanted to start a thread on “traditional navigation” in general, because it’s interesting. Most people are rather boring and like to push buttons and swipe screens, because that’s what they know, being generally unaware of other “ways of knowing”. The astrolabe was truly a multi-functional tool in the hands of a knowledgeable person - from figuring out Islamic prayer times, the direction to Mecca, identifying stars, determine the height of the sun, finding latitude, when to plant crops or collect taxes, even seeking astrological information/advice, when that sort of thing was seen as very important. Etc. Etc. A sort of computer of its day?
“The inventor of this remarkable astronomical device has been lost to history, although some scholars credit Hipparchus, an ancient Greek astronomer and mathematician, with the invention of the disk-like tool, based on evidence from 160 B.C. that suggests he determined the precession of equinoxes in Rhodes. However, the astrolabe began to be widely used during the height of the Roman Empire, sometime between the 2nd and 4th century A.D.
”In ancient times, the astrolabe was mainly used to tell the time, and not necessarily for navigation. This changed when the instrument was heavily modified and refined in the 9th century by scientists from the Islamic world.
”Astrolabe technology changed hands, spreading from the Islamic world to Europe through North Africa and Spain in the 11th century. By the 13th century, European usage of the astrolabe was widespread.
“It stayed in use for centuries by European and Islamic cultures up until the 18th century when it was replaced by more sophisticated technology.”
For “modern” navigation, apparently you had various ‘plates’, each etched with lines indicating star directions, etc., depending on what latitude you were at - so, navigators used a different plate for navigating the Mediterranean than for around the southern tip of South America.
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El Borracho
Barkeeper’s Friend
An astrolabe is simply a ruler with markings and tables of interesting values. Except in calibrated in parts of arcs rather than parts of lines. Handy for restive reclining old geezers because it does not require walking around to use.
Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #150
Yes, a form of slide rule. “Simply” indeed - but a very, very long-lived, multi-purpose device.
I’d love to read about someone crossing oceans with these nowadays, Sinbad-style. Now, if they had manufactured them in relatively thernally-stable plastic, like Davis sextants, they’d be lighter and easier to use for beginners (but would require some calibration?).
Cisco
Super Anarchist
I think the Rude Star finder and identifier is a descendant of the astrolabe.
https://aeroantique.com/products/rude-star-identifier-us-navy?variant=38657678154
https://aeroantique.com/products/rude-star-identifier-us-navy?variant=38657678154
gn4478
Member
Rasputin22
Rasputin22
- 14,574
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HTFU
Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #154
Love that pic - remember it from when I first read “Adrift” at my dad’s house many years ago.HTFU
Another good one (once you’ve mastered celestial nav, piloting, etc, etc):
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Jim in Halifax
Super Anarchist
Cisco
Super Anarchist
A bit of general confusion is creeping into the discussion.
The geographical positions of all heavenly bodies move westward across the face of the earth at 15º per hour ( OK I know there are siderial days and solar days but 15º will do for this discusion).
This means they move 1º in 4 minutes of time and in 1 minute of time their 'hour angle' or longitude will change by 15 minutes of arc. 15 minutes of arc in longitude is 15 nautical miles at the equator.
It follows that an error of 20 seconds of time in your calculations will lead to an error of 5 nautical miles at the equator.
As the length of a minute of longitude varies as the cosine of the latitude - from 1 at the equator ( 0º Lat) to 0 a the poles ( 90º Lat).
Bermuda is about 32º Lat so 1 minute of longitude thereabouts will be 0.8 nautical miles so the error will be in the order of 4 miles if there is a clock error of 20 seconds.
More important than having a perfect time piece is knowing the 'rate' of your time piece. A clock that gains a steady 10 seconds a day is better than one that gains 3 seconds one day and loses 7 the next and does who knows what on the next.
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Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #156
It’s been a year since the last update to this fine thread. Just came across this - seems like it belongs here. (From the 1936 comedy movie “Windbag the Sailor”.)
“Naviguessing at Sea”
“At last a short film that explains the arcane precepts of precision nautical naviguessing in clear concise terms even the meanest intellects will easily fathom.”
(From the good FB group “Practical Celestial Navigation” (hopefully visible without being a member of the group - but which is worth joining anyway, it’s a good one.)
“Naviguessing at Sea”
“At last a short film that explains the arcane precepts of precision nautical naviguessing in clear concise terms even the meanest intellects will easily fathom.”
(From the good FB group “Practical Celestial Navigation” (hopefully visible without being a member of the group - but which is worth joining anyway, it’s a good one.)
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Jud - s/v Sputnik
Super Anarchist
- Thread starter
- #157
Series of interesting talks by traditional Polynesian navigators and others who’ve worked with them (most notably “Mimi” George, who worked with well-known sailor/doctor/polymath Dr. David Lewis, who spent part of his life studying —and practicing— traditional navigation.) These were just yesterday published online by the esteemed Royal Institute of Navigation in London. (I think Captain Cook was a member?)
Well worth listening to the elders…if for no other reason than to marvel at what they did, that us modern-day weaklings cannot imagine
Well worth listening to the elders…if for no other reason than to marvel at what they did, that us modern-day weaklings cannot imagine
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