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Old 14-02-2011, 09:21   #46
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Originally Posted by goboatingnow View Post
Jeepers more myths about GPS

The coarse acquisiton signal ( C/A) is needed to use the precision one (P/Y) one cant be turned off on its own.

GPS is a worldwide asset, a fact ackowledged , most of teh worlds militaries can selectively deny GPS in a area if they desire. Hence turning off the system will never happen, short of global conflict.
Have a read of this article and tell me they can't shut off C/A and still use P/Y: SAASM and Direct P(Y) Signal Acquisition | GPS World
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Old 14-02-2011, 11:28   #47
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You lot are living in the past.

I think you are confusing the thought of redundancy with redundancy and either way its obsolete.

If you want to do something useful on a passage go download Stellarium and find out which star has been above your head for your whole life.

Sensational, free, and zooms in like a telescope


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Old 14-02-2011, 13:22   #48
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You lot are living in the past.
Thanks for the compliment -- I try to do my best.

I know sailing is old fashioned, but I still like it. Don't get me wrong, I've tried out a lot of the new forms of transportation, including helicopters, jets, and advanced naval vessels (though I've never been on any nuclear powered submarines, which IMO are the most advanced), but I still prefer sailing.

However, I must admit, I depend on my diesel more than I should, but I'm working on it.
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Old 14-02-2011, 13:33   #49
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Big Brother's control, conspiracy theories and Chicken Little warnings are not on my list of worries. I'm not one to see the glass half full or half empty. I know the glass is full and I keep track of what portion of the full volume is a liquid and a gas! New technology, as Mark J above cites, is amazing. I recently saw the ap on the I-pad that allows a full ID of star position and your orientation when held up to the sky. You can even read celestial positions beneath the horizon. I'm never without advocating a direct view of what's about the vessel, but I can't imagine people unable to accept the new technology that's available or discount it for fear that it might not always be available. That's like not learning to read for fear that you might be blind at some future date!
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Old 15-02-2011, 05:26   #50
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I know sailing is old fashioned, but I still like it. Don't get me wrong, I've tried out a lot of the new forms of transportation,
LOL.

Sailing here is so old fashioned they have different spellings for rum! Rhum being one. Can't pronounce it after a few, though


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Old 15-02-2011, 06:18   #51
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Big Brother's control, conspiracy theories and Chicken Little warnings are not on my list of worries. I'm not one to see the glass half full or half empty. I know the glass is full and I keep track of what portion of the full volume is a liquid and a gas! New technology, as Mark J above cites, is amazing. I recently saw the ap on the I-pad that allows a full ID of star position and your orientation when held up to the sky. You can even read celestial positions beneath the horizon. I'm never without advocating a direct view of what's about the vessel, but I can't imagine people unable to accept the new technology that's available or discount it for fear that it might not always be available. That's like not learning to read for fear that you might be blind at some future date!
Sorry you got that last sentence wrong....It should be.....
Its learning to read and reading everything on the planet now in case you go blind at some future date.

You can never know to much about navigation and learning while making you a better yachtsman can also be lots of fun and very interesting.
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Old 15-02-2011, 06:38   #52
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You can never know to much about navigation and learning while making you a better yachtsman can also be lots of fun and very interesting.
Thats like someone saying you can never know enough about Maths.... as they stand there with the latest 'bells and whistles' calculator...
The answer maybe right... but would/do folks understand how and why....
I was furious when my son was told a calculator was now a school tool years back.
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Old 15-02-2011, 08:49   #53
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I have a sextant on board, but I use my geiger counter more often...the last time I pulled it out, the lenses on the telescope were so moldy I could see through it, but I bought a new scope just in case I wanted to play with it.
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Old 15-02-2011, 08:55   #54
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Sailing here is so old fashioned they have different spellings for rum! Rhum being one. Can't pronounce it after a few, though
I'm sorta partial to scotch, but "when in rome..."

Btw, are you going to write up review of all the good bars down there? Can't wait to get out of here and get down there -- snow's nice, but this is getting ridiculous...
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Old 15-02-2011, 09:01   #55
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Celestial navigation will be here long after satellites fall out of the sky, and GPS can be suspended at any time (which was the cast back in the 90's during on of the Gulf wars).
That's flat-out wrong. What happened during the Gulf war was that selective availability was switched off temporarily, which made GPS more accurate during that time. The reason for this is that the US military didn't have enough of their own GPS units on hand for the operation, so they bought a truckload of commercially available units for the troops, then they switched off SA so that the troops on the ground would get a better fix.
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Old 15-02-2011, 11:06   #56
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Caveat: I am a stinkpotter now and mostly coastal, I can navigate with a pair of binoculars (nearsighted) and a compass.
However, back in my younger sailing days I picked up a brand new (read expensive!) Weems and Plath sextant and a complete Bowditch (this was in the early '70's) for a small sum from a guy who had received them as a gift from his parents and was stuck in Kingston, Jamaica trying to find a crew spot but needed cash now. I taught myself to use the sextant entirely from Bowditch and could typically get myself pretty easily on the right latitude within a half minute and within a degree of longitude which I considered pretty good. Since I was happy to be within 50 miles or so of where I thought I might be, missing markers and reefs where a non issue. Of course with a series of sights I might get as close as 25 miles but never did much better. I keep the sextant and still 'play' with it from time-to-time and if cruising open waters like some of you folks would definitely take it with me and practice with it for fun if nothing else. I notice now 40 years later that sailors (boaters?) seem to be impressed that you can use a sextant whereas they used to be surprised if you couldn't! My father was in the Army Air Corps in WWII and could should an accurate sight from an aircraft moving 120mph!
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Old 15-02-2011, 14:03   #57
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I have never seen a sextant on a boat since the early 1980's.
Hey Mark,

You didn't ask to see the one we had on board at the time (Tonga) . Never used in anger, tho', after 1.5 circumnavigations.

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Old 15-02-2011, 16:38   #58
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Jeepers more myths about GPS

GPS has never been suspended at any time since its activation, satellittes were repositioned to get greater coverage, but the system wasnt "suspended".
Selective Availability: Information from Answers.com

GPS can be adjusted, tweaked, and suspended at any time without notice by the United States and they disabled Selective Availability during the first Gulf War.

It is a question that all would-be UCSG captains get to answer on their exam, making it absolutely clear that you are not to rely on it as your only means of crossing an ocean.

If its just your life on the line, do whatever. But for a professional mariner who's passengers are expecting you to deliver them safely across open water there's simply a higher standard to be held. The UCSG doesn't require celestial navigation for cross ocean transit because they're a bunch of fuddy-duddies in white ascots.

It was RDF, then it was LORAN, now it's GPS. There are other electronic aids to navigation that will undoubtedly replace GPS in the next few decades as the EU and other groups put more satellites up. Being knowledgeable in current technology with zero capacity to safely deliver a vessel across an ocean if that technology fails is hardly good seamanship.
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Old 15-02-2011, 18:30   #59
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Originally Posted by MarkJ
I have never seen a sextant on a boat since the early 1980's.

G'Day Mark,

I suspect that you just never got past the liquor locker when you searched all those other boats that you've visited since 1980.

And should you ever visit Insatiable II, you will again be on a boat that has one aboard. Ann and I started passage making in 1983, long before GPS and when the Transit sat-nav was really expensive. At that time, celestial was the only off-shore navigation method available to the non-rich yottie, so that's what we did. Still have the sextant aboard, still sorta remember how to use it, feel very sure that I could come back up to speed if required, and do carry enough paper stuff to work out a position.

Honestly, the last time the sextant was out of the box was to observe a solar eclipse!

But to answer Greg's question, we do still carry the archaic instrument.

Cheers,

Jim and Ann s/v Insatiable II lying Castle Lagoon, NSW, Oz
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Old 15-02-2011, 19:08   #60
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GPS can be adjusted, tweaked, and suspended at any time without notice by the United States and they disabled Selective Availability during the first Gulf War.
Which on course made it more accurate for all of us !!

Look arguing that sextants are valuable because gps could be turned off or fall out of the sky or whatever is a ridiculous argument. Celestial navigation also relies in some part on technology. Ie almanacs and sight reduction tables.

It is also ridiculous to suggest it is imprudent to cross oceans relying on gps. There are several other techniques then using a sextant.

GNSS is here to stay , live with it. If you want a safety belt then brush up on other techniques as well. Don't justify celestial usage by suggesting far fetched GPS /GNSS failure modes.

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