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Old 29-07-2020, 23:43   #1
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wood ships , iron men

The wisdom is that clocks were needed for longitude. A uni prof of polar history tells me that early sailing ships were unable to return to a specified position. But hang on, that was before 1760 and since 1500 there were European colonies in Americas and Asia.

Maybe you can't buy an hour-glass (they were 1/2 hour) which were corrected for time at sunrise. But how real was the problem? One minute-time is about 17miles spin at equator, say 8 miles either direction. So a 20ft mast gives sight to a 20ft hill at about 10miles. The destination can only be ahead , not astern. Latitude is fairly definite. 5 minutes error is say 85miles spin. Running to a N-S coast at night is a worry but probably not usual , slacken off and wait for tomorrow.

I know nothing about the subject and would like any input about what I don't know .
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Old 30-07-2020, 01:41   #2
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Re: wood ships , iron men

It's true that a chronometer is needed for a more accurate determination of longitude. But dead reckoning can still get you close. However, sometimes "close" is not good enough. The story goes that, among other things, the disaster at the Scilly Isles in 1707 prompted the offering of a prize for a solution to the longitude problem. The reasoning was that if an accurate method of determining longitude had been available, the ships would not have run aground. Between 1,400 and 2,000 men lost their lives in that one disaster, so yes, it was a real problem.



As for the assertion that ships could not return to a specified position: well, that's not entirely true. Yes, it would be difficult to return to a specific spot in the [ant]arctic regions or in the middle of the ocean, due to a general lack of identifiable features. But returning to a specific location such as one's home port was - I dare say - not an uncommon skill amongst pre-chronometer mariners. Otherwise I don't think sailing would have really taken off.



As you point out: people were sailing successfully from port to port all over the world long before the invention of chronometers, and even before sextants or cross staffs. And latitude sailing was certainly done. So, is a chronometer "necessary"? No. Can it make a voyage safer and more efficient? Yes.
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Old 30-07-2020, 02:09   #3
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Re: wood ships , iron men

Righto. This trip was about 2500 miles across from India . Maybe not an "accident" in 8th century?
https://phys.org/news/2012-03-indone...car-years.html
Indonesian 'Eves' colonised Madagascar 1,200 years ago* **phys.org*› Biology › OtherMar*21, 2012 -*with a smattering of words from*Javanese, Malay or Sanskrit.A team led by*molecular biologist*Murray Cox of New Zealand's Massey University delved into DNA for clues to explain the migration riddle.

" Yet a third -- and more intrepid -- hypothesis is that the women were on a boat that made an accidental transoceanic voyage. That notion is supported by seafaring simulations using ocean currents and monsoon weather patterns, says Cox's team."

The voyage is assumed to be Sumatra-India , about 1000miles. The whole trip was 3500miles so probably the last 2500 would be drifting at 1.5knot on Equatorial current , doubling the normal ship 3knot on course. Food would be unlikely to be stored , with surplus for planting in Madagascar and feeding them until harvest. Why would farmers with tools be on a merchant ship? It points to planning and reliable navigation. The contacts with Java continued until 1500s so somebody returned with the news.
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Old 30-07-2020, 03:41   #4
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Re: wood ships , iron men

The voyage of the 'Trinity' in 1681 may be of interest.

Having had their way with the locals on the west coast of SA, Peru etc, Basil Ringrove and his buccaneer chums departed Paiti... near Guayaquil, Ecuador ... bound south.

Next landfall was Islas Duque de York - which they named- , Patagonia, just north of Estrecho de Magallanes. Leaving there they were driven south of the Horn... further south than any before them and becoming the first englishmen to 'double the Horn' eastwards.

Moving right along.... after three months and 9000 miles out of sight of land they reached the latitude of Barbados on 18th January 1682... hung a left and sighted Barbados on the port bow ten days later....

So yes... you can get by without a clock....
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Old 30-07-2020, 03:50   #5
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Re: wood ships , iron men

There is a great book by Dava Sobel about this topic: 'Longitude'. There's also a movie made of it.
It tells the story of the Harrison Chronometers.
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Old 30-07-2020, 03:55   #6
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Re: wood ships , iron men

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Originally Posted by Andreas W View Post
There is a great book by Dava Sobel about this topic: 'Longitude'. There's also a movie made of it.
It tells the story of the Harrison Chronometers.

https://www.amazon.com/Longitude-Gen.../dp/080271529X
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Old 30-07-2020, 04:54   #7
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Re: wood ships , iron men

Your Uni-professor was wrong.

They were able to get to a known destination by going north/south until they were on the same latitude as the destination and then turn east/west and stay on that latitude...this will get you to the destination.

There are a few problems thought. It often means you are traveling much further than if you took a great circle route toward your destination. It also might force you to sail against current/winds or thru doldrums.

Coastal sailing, if you can see landmarks periodically, dead reckoning is an option but they had to be careful of currents. For ocean crossings where it might be weeks between sight of land, the inaccuracy of dead reckoning was generally too much but say once they found a known Caribbean island, they could then island hop using dead reckoning.

In many ways, a portable clock that worked accurately at sea is the reason for Britain became a world power.
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Old 30-07-2020, 07:07   #8
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Re: wood ships , iron men

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Your Uni-professor was wrong.

They were able to get to a known destination by going north/south until they were on the same latitude as the destination and then turn east/west and stay on that latitude...this will get you to the destination.

There are a few problems thought. It often means you are traveling much further than if you took a great circle route toward your destination. It also might force you to sail against current/winds or thru doldrums.
If you had to cross the doldrums to get to your destination you had to cross them regardless of the route you took. A problem could emerge if your destination was in the doldrums, which brings me to a second point. You don't have to start by sailing to the latitude you want and then turning left or right to sail along that parallel. if prevailing winds/currents dictated you could use dead reckoning to cross the ocean and then sail north/south to the latitude you want. The Americans were generally better at this than the Brits which helped when it came to trade. The first chronometers were very expensive, complex, sensitive devices. Not everyone could afford one. I know when I first did an ocean passage using celestial the availability of cheap quartz watches and WWV broadcasts made life so much easier. Now position-finding is so simple it is hard to remember how hard it was at the time of Cook who was an outstanding navigator.
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Old 30-07-2020, 08:41   #9
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Re: wood ships , iron men

Lunars. They knew how to get the time through lunar observation. That's probably how Slocum managed to navigate with a $2 tin clock.
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Old 30-07-2020, 09:21   #10
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Re: wood ships , iron men

valhalla 360.I read that they would go south until the butter melt and then cross to known region.
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Old 30-07-2020, 11:05   #11
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Re: wood ships , iron men

Think professor incorrect. Otherwise how did they return to tell the tale?
Chronometers were a huge technical advance but not any different than the sextant , the electronics, etc.
on the polar issue the confusion came from minimal landmarks and ice limits, but during clear weather the stars were utilized.
Recall that as technology advanced so did experience.
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Old 30-07-2020, 13:39   #12
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Re: wood ships , iron men

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Originally Posted by fouled View Post
The wisdom is that clocks were needed for longitude. A uni prof of polar history tells me that early sailing ships were unable to return to a specified position. But hang on, that was before 1760 and since 1500 there were European colonies in Americas and Asia.

Maybe you can't buy an hour-glass (they were 1/2 hour) which were corrected for time at sunrise. But how real was the problem? One minute-time is about 17miles spin at equator, say 8 miles either direction. So a 20ft mast gives sight to a 20ft hill at about 10miles. The destination can only be ahead , not astern. Latitude is fairly definite. 5 minutes error is say 85miles spin. Running to a N-S coast at night is a worry but probably not usual , slacken off and wait for tomorrow.

I know nothing about the subject and would like any input about what I don't know .

To understand their navigation it is maybe good to take in account that they had large crews, and used them also for intense human sensoring : always lookouts up in the mast, watching carefully for any signs of land proximity on the water - plants, debris - and birds flight, manually depthsounding at any suspicion with sample collection of bottom material. And when approaching unknown shores sending small tender boats ahead to investigate. After contact with natives hiring local sea/fishermen as pilots. Latitude only navigation is like knowing the name of the street but not the number of the address; but at the end of the street, or reaching land, you are where you want - with hopefully no unknown obstacles on that line.
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Old 30-07-2020, 13:48   #13
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Re: wood ships , iron men

Tired wheelsmen would turn the hour glass before time and this would foul up longitude.
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Old 30-07-2020, 14:10   #14
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Re: wood ships , iron men

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Originally Posted by AiniA View Post
If you had to cross the doldrums to get to your destination you had to cross them regardless of the route you took. A problem could emerge if your destination was in the doldrums, which brings me to a second point. You don't have to start by sailing to the latitude you want and then turning left or right to sail along that parallel. if prevailing winds/currents dictated you could use dead reckoning to cross the ocean and then sail north/south to the latitude you want. The Americans were generally better at this than the Brits which helped when it came to trade. The first chronometers were very expensive, complex, sensitive devices. Not everyone could afford one. I know when I first did an ocean passage using celestial the availability of cheap quartz watches and WWV broadcasts made life so much easier. Now position-finding is so simple it is hard to remember how hard it was at the time of Cook who was an outstanding navigator.
You could cut some corners. Ie: if you are running from UK to the Bahamas, you could start out on a generally SW heading but at some point without longitude, you have to either find a known point of land to reset your dead reckoning or switch to the latitude and turn right method. The problem is after a few weeks at sea, your dead reckoning estimate of longitude could be off by hundreds of miles. If you accidentally got too far west before you got far enough south, the gulf stream would really muck up your trip.

Yes, they were expensive and in the early days, the big military ships got them first. They were closely guarded so other nations couldn't get hold of the technology. Eventually, they spread to commercial ships and other nations but by then Britain was the power house of the oceans. In a similar transit, with an estimate of longitude, they would know they are heading for the N. Carolina coast and the Gulf Stream long before they reached there and could take action by heading further south.

Also, with an estimate of longitude, the brits could start to plot out the major ocean currents far more accurately.

You can argue head south and then turn right is a bit of an oversimplification but they didn't put all that effort into a reliable means of determining longitude for nothing.
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Old 30-07-2020, 15:07   #15
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Re: wood ships , iron men

The head of the Royal Observatory was trying to develop the ability to determine longitude via shots of the moon. To further his ends he threw everything he could in the way of developing the chronometer. The inventor of the first viable chronometer went through incredible hardship largely at his own expense over more than a decade to design a large pocket watch size chronometer. His first successful chronometer was the size of a suitcase which he refused to use to claim the multimillion pound prize for the first successful chronometer.

Even with a chronometer navigation was chancy if there was long lasting overcast. The Pilgrims landed at Plymouth Rock when they were supposed to be setting up a colony in Virginia. The captain was navigating via Latitude but got very off course probably because of long term overcast.
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