Celestial Navigation? Forget it! - Page 15 - SailNet Community
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post #141 of 330 Old 10-24-2006
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I said I wouldn't comment any further but just had to!
SD...I agree that relying on a GPS map and pointer is dangerous. I have a plotter but it is my lat/long readout that I check on my PAPER charts. I agree that anyone who doesn't use paper and know where they are at all times AND keep a sharp lookout is a hazard to navigation.
So I will hopefully close out once and for all on this happy note!
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post #142 of 330 Old 10-24-2006
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paper charts can be off a little, too. usually they're still consistent enough to the actual landscape so bearings will pinpoint your position in regard to the landscape close enough, if maybe not to the lat/lon grid.
and that's sure a problem with GPS, it might tell you where you are in regard to the grid, but NOT if the features on your chart, both electronic or paper, are exactly where they should be.

for me that means, when i'm in sight of land, i determine distance to danger by what i can make of the features rather than numbers, be it GPS or celestial.

once land is out of sight GPS is good enough to guide me.
and yes i do own a sextant and sometimes i do take sights, usually in competition with my father who takes sights every day, weather permiting, from the terrace of his retirement home.
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post #143 of 330 Old 10-24-2006
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GPS accuracy and stuff...

G'day All, really enjoying this thread, thought I'd chip in my 2 bobs worth...

A couple of years ago I worked on a large US military HQ, they had a dude who's job was to track and report GPS accuracy data. Turns out there is a couple of times each day when the accuracy blows out to 10's of thousands of metres - bad when you use it to aim 2000lb bombs! Anyway, its only a couple of times each day, but your GPS doesn't know - it will happily report "accuracy 5m" or whatever. Food for thought?

I'm no luddite; I rate my GPS and use it all the time - at work, in my kayak and on my boat, but it's been bashed into me over the years that GPS is an aide to navigation, just like a map/chart. In my kayak (and on the boat) I have a kamal, which I calibrate using the Southern Cross, which I can use to measure distances from points - quite handy for coastal nav in the kayak. I can also use the sextant to measure angles/heights, which comes in handy sometimes too (I'm still teaching myself to do proper CELNAV).

The fact is, all the kit (GPS, sextants, kamals, charts...) are just tools in the toolbox - and its like the old saying "if all you have is a hammer, every problem is a nail".

Just my 2 bobs worth
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post #144 of 330 Old 10-24-2006
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Camaradarie:

Sorry I wasn't more explicit with my meaning of "self-contained." By self-contained, I mean everything I need to find my position is on the boat. My chronometer has a fixed gain rate. I only need to check time maybe once a month, well within any ETA. Even if the clock and radio fail totally, I can find my position by lunar distances or run down my latitude. My HO229 is also 30 years old, has been wet many times and is still perfectly readable. I've never had to repair my sextant, but if I did damage it, I have a plastic backup I bought 30 years ago for $20. I'm practiced enough to reduce three sites in 30 minutes and that's never been too long.

GPS is NOT self-contained because it depends on satellites operated by a goverment which can alter their accuracy for legitimate reasons of defence any time. There are other reasons, not preferential, that can damage the system as well. Not likely you say? Maybe not. But I'm still self contained.
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post #145 of 330 Old 10-27-2006
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Cool no celestial navigation?

Well, seems to me that your nick explain a lot of your statement. An artist escaping. Also looks like you sail every time under radio reach and can call for dad's help at any time you are on that litle bay you are sailing. Realy no need of CN then. BUT, if you are doing some seriousily sailing, enganged on long voyages...NO CN, no way home...
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post #146 of 330 Old 11-05-2006
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Navigation is essential for any vessel afloat. While electronics are very accurate and labor-saving. an appreciation of the basic skills of piloting and celestial navigation can still be very helpful and they add to a complete understanding of the subject.

Piloting is the ability to navigate from lines of position, navaids, and soundings when in proximity to the coast. It is quite helpful even when using GPS. Everyone should know how to do the basic things. If nothing else, it helps to pass the time when you have the deck watch if you know the geometry behind simple tricks like doubling the angle on the bow, or the use of the manuevering board for predicting relative movement.

Celestial navigation is a skill for deep water. Those engaged in, or contemplating a long distance voyage should know some fundamentals such as longitude by local apparent noon and latitude by Polaris. It really isn't hard, doesn't require batteries (except for your watch), and adds to your confidence when you won't see land for a while.
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post #147 of 330 Old 11-05-2006
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I guess it depends on where you're going. If you're on your way to Hawaii when the GPS fails, you're in trouble. If you're on your way back from Hawaii, not so much (I'm pretty sure I could hit the West Coast even without a compass.) And failures are not all that unlikely, when you put all the risks together (lightning strike, alternator failure, engine failure, military action...) When you're betting your life, you want to reduce risk to as near zero as you can.

It's a matter of good seamanship, it seems to me, that it is incumbent upon a sailor to know where he is no matter what.

They have GPS on golf carts, you know. Good golfers can judge what club to hit with the GPS or without, but bad golfers can't.
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post #148 of 330 Old 11-06-2006
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I believe it would be "fun" to learn CN and that is about it. Let's take the extreme example of heading for Hawaii. If thhe military turned off theGPS they would turn it back on long before CN was going to save your ass.
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post #149 of 330 Old 11-06-2006
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I think that GPS are one of the worst things that ever happened to sailors...
For instance I read an article somewhere about a 34 ft sloop that was crewed by so called "experienced sailors" and their GPS happened to fail in a remote bay full of reefs, and the boat sank and two of the crew members were drowned... apparently they had been fine in other shoals when the gps had been working
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post #150 of 330 Old 11-06-2006
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Oh yeah...well I read about this guy who didn't have any GPS and he couldn't get a sun sight for 40 days and it rained and stormed and when it finally stopped and the sun came out, he found himself hard aground with no idea where he was. His name was Noah something or other....

Sorry...couldn't resist
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