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Old 11-08-2012, 22:53   #16
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Re: Recommended Sources to Lear To Use a Sextant, etc

Tom
In all reality, celestial navigation is not something you can rely on for coastal navigation. Any clouds, fog or particulates in the air will prohibit your ability to get even one good LOP.
Next, I noticed that you are sailing some pretty small boats; VERY VERY hard to get an accurate sight on a 40 to 50' boat under sail in lousy weather, let alone something in the 20' range. And you need some books; don't let them get wet!
For the price of a good sextant, a very accurate time keeping system (4 seconds error in time is 1 mile in navigation) sight reduction tables & a few stopwatches, you could probably buy a couple of back-up gps units.
Don't get me wrong, I think it's admirable that you want to learn to navigate with a sextant, but do not think that it is a reliable back-up for electronic navigation.
I circumnavigated from 1970-1979 & other than RDF, I used celestial with DR. There were periods of days (6 days from New Caledonia to Australia into the Great Barrier Reef) when I could not get a sight. Going up the Red Sea, there was so much sand & heat from the deserts that celestial was useless.
Do not fall into the electronic time giving equipment fiasco. After a hurricane in the SoPac we lost our radio & we had no chronometer, therefore, we had no time!!!! Not smart! A chronometer is not a perfectly accurate clock; it is a time piece with a consistent predictable error.
Some of these "new fangled" inventions are truly lifesavers, use them with confidence, and back-ups of course.
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Old 12-08-2012, 00:04   #17
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Re: Recommended Sources to Lear To Use a Sextant, etc

Understood, but my long term plans include getting a bigger boat and going out a lot further.

As to timepieces, I have a Rolex, and it's accurate to about a minute a month. I've checked it's calibration off of the UT Shortwave atomic clock. I know it's accuracy, and my backup is a Bulova that is also very accurate and a known gain of 2 minutes a month..

Also, if I have all backups crap out, I don't want to be using dead reckoning trying to find port for repair or replacement. I'm a firm believer in multiple redundancy.......then again, I am a database administrator, and somewhat OCD about backupdata, and navigational data is just that.......data, to me, and data my life may depend on. I have lots of motivation here.

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Tom
In all reality, celestial navigation is not something you can rely on for coastal navigation. Any clouds, fog or particulates in the air will prohibit your ability to get even one good LOP.
Next, I noticed that you are sailing some pretty small boats; VERY VERY hard to get an accurate sight on a 40 to 50' boat under sail in lousy weather, let alone something in the 20' range. And you need some books; don't let them get wet!
For the price of a good sextant, a very accurate time keeping system (4 seconds error in time is 1 mile in navigation) sight reduction tables & a few stopwatches, you could probably buy a couple of back-up gps units.
Don't get me wrong, I think it's admirable that you want to learn to navigate with a sextant, but do not think that it is a reliable back-up for electronic navigation.
I circumnavigated from 1970-1979 & other than RDF, I used celestial with DR. There were periods of days (6 days from New Caledonia to Australia into the Great Barrier Reef) when I could not get a sight. Going up the Red Sea, there was so much sand & heat from the deserts that celestial was useless.
Do not fall into the electronic time giving equipment fiasco. After a hurricane in the SoPac we lost our radio & we had no chronometer, therefore, we had no time!!!! Not smart! A chronometer is not a perfectly accurate clock; it is a time piece with a consistent predictable error.
Some of these "new fangled" inventions are truly lifesavers, use them with confidence, and back-ups of course.
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Old 12-08-2012, 08:41   #18
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Re: Recommended Sources to Lear To Use a Sextant, etc

Quote:
Originally Posted by capta View Post
Tom
In all reality, celestial navigation is not something you can rely on for coastal navigation. Any clouds, fog or particulates in the air will prohibit your ability to get even one good LOP.
Next, I noticed that you are sailing some pretty small boats; VERY VERY hard to get an accurate sight on a 40 to 50' boat under sail in lousy weather, let alone something in the 20' range. And you need some books; don't let them get wet!
For the price of a good sextant, a very accurate time keeping system (4 seconds error in time is 1 mile in navigation) sight reduction tables & a few stopwatches, you could probably buy a couple of back-up gps units.
Don't get me wrong, I think it's admirable that you want to learn to navigate with a sextant, but do not think that it is a reliable back-up for electronic navigation.
I circumnavigated from 1970-1979 & other than RDF, I used celestial with DR. There were periods of days (6 days from New Caledonia to Australia into the Great Barrier Reef) when I could not get a sight. Going up the Red Sea, there was so much sand & heat from the deserts that celestial was useless.
Do not fall into the electronic time giving equipment fiasco. After a hurricane in the SoPac we lost our radio & we had no chronometer, therefore, we had no time!!!! Not smart! A chronometer is not a perfectly accurate clock; it is a time piece with a consistent predictable error.
Some of these "new fangled" inventions are truly lifesavers, use them with confidence, and back-ups of course.
I don't believe the OP was looking for a replacement system, the way I took it was he wanted a separate backup. The point of a such a backup would not be coastal sailing, but to make the first landfall then find repair for whatever brought the GPS system down.

Great accuracy is not necessary, or even mediocre accuracy, the idea is to correct your DR position for whatever inaccuracies creep in.
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Old 12-08-2012, 10:13   #19
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Re: Recommended Sources to Lear To Use a Sextant, etc

I have found this one an easy read and pretty complete:

Complete On-Board Celestial Navigation: Nautical Almanac and Sight Reduction Tables 2011 - 2015

(author: George Bennett)

I used printed copy but now it comes as an ebook ;-(. You can probably get a printed s/h copy for next to nothing.

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