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Old 18-02-2010, 13:48   #61
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...and I love the absurdness of the fact that when I take out my sextant to practice an observation, I proceed to do the calculations with a UTC time from .... the GPS!
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Old 18-02-2010, 13:57   #62
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Even that it matters.
Should be "Enough that it matters." It's all shades of grey and subjective value judgments.
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Old 18-02-2010, 14:05   #63
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has anyone else seen the original timepiece by i think a guy called harrison? Its in one of the London museums.Its certainly a lot larger then its modern wrist born acessories.

I had a quick look at the links to celestial navigation,my first reaction was "yuk" at the math involved.

it does apeal to me to learn the skill of using a sextant,but it is a skill that i will not require untill i head out to a larger Ocean,as long as i keep up my log entries,the chances of me becoming lost in the Southern North Sea are slim.
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Old 18-02-2010, 14:08   #64
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Hank-
If you do a web search, there are a number of free sight reduction apps out there for computers and for PDAs. John Manson's "Navigation" package for the Palm PDA is a good one, and you can buy an inexpensive used Palm PDA to dedicate for the task. (Palms are much more well-behaved than laptops and run for weeks on 2xAAA cells.)
.
I have an old Palmone PDA,do you know if the software will run on that?
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Old 18-02-2010, 14:38   #65
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...and I love the absurdness of the fact that when I take out my sextant to practice an observation, I proceed to do the calculations with a UTC time from .... the GPS!
Relatively inexpensive wrist watches are available now that are damned accurate, even after a year. If you know your wristwatch rate of error, it makes your wristwatch even more accurate. This is exactly how it was done with three chronometers on a ship. The chronometer error was logged. Many wristwatches now are accurate enough to get accurate longitude, where 4 seconds of time accuracy equals one nautical mile of accuracy for longitude. That's 900 nautical miles per hour that the sun moves around the Earth....from a celestial sphere perspective of course.

See what you anti-celestial types are missing out on? Interesting trivia like this! You people may as well throw overboard your books on ocean life, the history of cultures that you are going to visit and other non-essential information as well. Heck, just stay on board and never venture ashore to learn new things. Perhaps just watch reruns of Cops while sitting at anchor? Just kidding of course, but you get my point.
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Old 18-02-2010, 15:27   #66
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Great post David! Learning what can be learned and the steps along the way brings a knowledge that is uplifting! When one starts understanding the relationship behind degrees and distance, angles etc, one begins to see why math was invented and can sometimes even loose the phobias assoceated with it! It is only a language to discribe our environment. When you see the whys and hows, the abstract language can start to make sense. What the ancients up to pressent day have figured out is amazing and learning how to use a sextant can be increadibly rewarding!
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Old 18-02-2010, 15:30   #67
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has anyone else seen the original timepiece by i think a guy called harrison? Its in one of the London museums.Its certainly a lot larger then its modern wrist born acessories.
An excellent movie was made about John Harrison and his chronometers. Longitude (2000) (TV) Probably out on DVD.
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Old 18-02-2010, 15:43   #68
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An excellent movie was made about John Harrison and his chronometers. Longitude (2000) (TV) Probably out on DVD.
Great book on the same subject:

Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time
by Dava Sobel

http://www.amazon.com/Longitude-Geni...6532900&sr=1-7

The English government cheated him out of the prize money. Very interesting story about power.
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Old 18-02-2010, 15:54   #69
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i was not aware that Harrison was cheated out of his prize money,the Admiralty had offered a prize of 10,000 GBpounds to the person who invented the timepiece.
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Old 18-02-2010, 16:06   #70
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I forget the details but basically they didn't pay him until he was a very old man (late 70s). He was much younger when he first came up with the time piece. He ended up making four versions trying to get the prize money. They kept the timepieces to add insult. They also changed the rules midstream in order to deny payment.

Eventually he was paid, but not by the party who made the initial offer. It was a very disreputable thing they did to him. He spent much of his life trying to get the prize money, nearly fifty years.

The prize money was offered to solve the "longtitude problem." A timepiece was but one approach--Harrison's approach and ultimately the best approach.

The basic problem was that Harrison was a nobody (a simple clockmaker), and there were notable scientific 'names' after the prize money too. Said persons used their pull to have the prize withheld as most of the scientific community felt answer to the riddle lay in the heavens alone. All very sordid.

I don't really remember, but I think he never did get full payment. Harrison bested the best scientific mind's of his day, and they never forgave him for it. And they held the power.

The book was a good read.
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Old 18-02-2010, 16:15   #71
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I carried my trusty Tamaya for many thousands of miles but only used it for diversion (the chess analogy is apt). Still the backup aspect is very real. I have only done two ocean crossings; on both my sextant had an LCD watch on the handle, set to UTC before departure, along with the marine tables plus the appropriate almanac pages. Of course it was not likely that either the GPS system would drop or my multiple GPS units would fail, including the AA battery powered handheld, just while I was out in the middle of the ocean. It is comforting nonetheless.

I have spent far more time coastwise and island hopping, and GPS has indeed failed me at critical moments. I am not about to forget the week number rollover problem that struck when I was on the Markermeer heading to Amsterdam - the marina that evening was full of sailors trying to get their GPSs to work. I have also enjoyed local blackouts courtesy of Navy tests of their jamming equipment (announced on Navtex and the local Notices to Mariners, which everyone is following, right?). The prudent mariner never relies on any one system - even one as good as GPS.

My first line of defense (after multiple, independent GPS receivers) is my other electronic gear: radar, depth sounder, knotmeter, heading sensor, etc. I have known vessels to lose all electronic gear, including GPS, when struck or nearly struck by lightning. So my second line of defense is an adjusted (swung) compass, a trailing log, lead line, and my sextant. Unfortunately the compass is not immune to error caused by the field of a lightning strike but there are no guarantees in life. Finally, being a little paranoid and recording position data in potentially dodgy situations (fog, rain, gales, out of sight of land, etc) doesn't hurt.

I would recommend carrying a sextant as a backup, but only after a lot of other backup and safety equipment has been acquired first. Unless you are someone who just wants to go back to the old ways, in which case more power to you.

And for the record, a lot of marine publications that are published in both the US and the UK (including the Nautical Almanac) are actually a collaboration - an error in one will be in the other as well. Conspiracy theorists can have fun with that.
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Old 18-02-2010, 16:20   #72
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Brit history is full of stuff like that,in the days when we had to tip our caps to those with the titles and the money.John franklin was creditied with discovering the North West Passage when in fact a Scotsman called john rae was the first European to do it. The guys mistake was to report back with the truth and this enraged Franklins widow who used her money and influence to have her husband acredited with the discovery.

getting back on topic,i wonder if John rae used a sextant
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Old 18-02-2010, 16:34   #73
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I had a quick look at the links to celestial navigation,my first reaction was "yuk" at the math involved.
Hwat?

I think the math involved is very simple: adding/deducting/multiplication/division. And you can make it even simpler by using logarithms. In fact you can skip all this by using sight reduction tables.

b.
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Old 18-02-2010, 16:37   #74
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I have spent far more time coastwise and island hopping, and GPS has indeed failed me at critical moments.
I have had the chartplotter locating the boat on dry land while cruising in Alaska.

And closer to home in nearby Canadian waters they have had the boat about 300 yards farther south than actual location.

Them chartplotters are just an invitation to disaster if you don't regularly second guess them. These people who transfer their video skills to navigation scare me.

I have a powerboater friend who is into all things electronic. He has multiple very expensive chartplotters. That they might incorrectly situate his boat relative to land or rocks has literally never occurred to him, and he will not listen to me because I'm perceived as a Luddite.

And I swear he may runover some kayakers some day.
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Old 18-02-2010, 16:38   #75
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Hwat?

I think the math involved is very simple: adding/deducting/multiplication/division. And you can make it even simpler by using logarithms. In fact you can skip all this by using sight reduction tables.

b.
You still have addition and subtraction, even with sight tables.
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