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Old 02-10-2007, 12:01 AM   #1
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GPS or Sextant?

Is it a dieing bred to navigate via the sky, sextant and charts?

Are sailors relying solely on GPS with no alternate methods or back up systems?
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Old 02-10-2007, 12:36 AM   #2
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The backup is to have a handheld GPS. Much safer and far more accurate. Cost less and you don't have to worry about being 50 miles off in position and trying to keep a dead reckoning log. You know your position to within a few meters anytime of the day or night, cloudy skies, bad weather, etc. Quicker, cheaper, more accurate and alwats up to date.

I don't use Loran, morse code on the radio, wood blocks, or a horse and buggy. It's called progress.
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Old 02-10-2007, 12:50 AM   #3
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Just to add to Spike_dawg's good advice:

The back-up (second) GPS will normally be a hand-held and NOT a second boat GPS - DIFFERENT power source.

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Old 02-10-2007, 05:54 AM   #4
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Spike dawg, and Admin,

Thanks. I like the answers and the solution. I like progress and understand that concept.

I really am not super motived to learn navigation with a sextant, being a product of the technological age, yet feel I must, at least should.

My training and expeiance tells me to plan for and have backups and alternate plans.

Should one loose the main boat and it's systems, the handheld would be useable in the life raft. Provided one gets it there in working order, batteries included. At that point it may or may not be to important to know "Where are we?" compared to: was the MAY DAY signal received, are we sending a signal, when may help arrive, and how much water, food and floatation did we save?
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Old 02-10-2007, 07:00 AM   #5
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Aqua Man

First, if you haven't already, go take some basic Rules of the Road and DR Navigation courses.

Then, buy Navigator 4.5 with Star Finder. It is much better than Star Pilot IMHO. It is written by a Brazilian programmer Omar Reis with a lot of talent and the cost is less than half that of Star Pilot. It makes learning to use your Sextant quick and easy.

http://www.tecepe.com.br/nav/

Using the sextant is a great way to pass the time while cruising and it gives you a nice warm since of security that you have the ability to navigate without GPS.

Cheers,

Ken
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Old 02-10-2007, 07:13 AM   #6
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Sextant navigation is an oddity in the modern world, but I still enjoy taking sights to 'prove the GPS' on occasion. It can be fun also to plot position using the sextant to determine recripocal bearings from shore based objects when coastal cruising, and there is no better way to see a solar eclipse than through the filters on your sextant.

However, I trust the GPS far more than the sextant and I reiterate, in my opinion the sextant in today's age is an oddity.

David
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Old 02-10-2007, 07:24 AM   #7
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Some may argue otherwise, but I strongly believe a severe solar storm could leave a large number of cruisers flying blind on the open seas one day.

================================================== =================

SOLAR flares can drown out GPS signals with potentially serious consequences for airlines, emergency services, and anyone relying on satellite navigation.

It turns out these bursts of charged particles, which produce auroras and geomagnetic storms, also generate radio waves in the 1.2 and 1.6-gigahertz bands used by GPS.

How was such a clash missed? Because GPS receivers only became common during a period of low solar activity. By 2011 solar flares will reach the peak of their cycle and receivers will likely fail. Or so Alessandro Cerruti of Cornell University, New York, told a meeting of the Institute of Navigation in Fort Worth, Texas, last week. The only solution would be to redesign GPS receivers or satellites, which may not be practical, says Cerruti.

From issue 2572 of New Scientist magazine, 07 October 2006, page 27
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Old 02-10-2007, 07:58 AM   #8
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Another good article:

http://science.nasa.gov/headlines/y2006/10...tormwarning.htm
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Old 02-10-2007, 09:25 PM   #9
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It is important to still plot your position on a paper chart - we did it every hour.
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Old 02-11-2007, 02:16 AM   #10
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No doubt! I just wonder how many sailors actually do it.
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Old 02-11-2007, 03:41 AM   #11
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We rely soley on GPS - and have two backs up - one with differing power source. We also do note position / course / speed each hour to paper just in case we need to revert from plotter to paper chart. Never yet had to do so.

However, have seen GPS switched off for a period around start of first gulf war which was a bit diconcerting as we were out of sight of land, racing, and not kept paper records of positions. Fortunately our estimates were not too far off and we hit shore about right spot.

But to counter those who warn GPS might fail for whatever reason - lets not forget the sun and a sextant are not 100%` either. If you've a week of cloud and no ability to take sun or star sights - your sextant is only useful as a backscratcher!!

Cheers

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Old 02-11-2007, 06:52 AM   #12
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Quote:
Originally Posted by name='Converted Post'
Originally posted by Trim50

No doubt! I just wonder how many sailors actually do it.
When the Magellan GPS first came out, Peter bought one, ridiculously expensive as they were. In 1990 we were sailing up the Costa Rican coast when we heard two boats, sounding a bit panicky, complain that their GPS had stopped giving positions. The US military was fiddling with the satellite transmissions and there were limited positions given over a period of several days. One could query the GPS for the schedule of the satellite down time, so there should not have been so much worry on the part of these boats. They obviously had not been keeping a DR log, and I got the impression they didn't know how to plot a DR course.

I don't expend much energy feeling sympathy for people who leave the comfort of modern civilization without preparing themselves for the consequences of that decision. Yet marketing departments of the various GPS manufacturers aren't about to warn their potential customers of the problems they might have. Most navigation courses, though, do emphasize the importance of preparation and course logs.

Listening to panicked voices on the VHF, hearing about the silly mistakes that people make on the water, and watching boats follow their chart plotter slavishly, afraid to deviate course even by a degree, I would say that there are too many people out there without the necessary preparation to go offshore. As a woman, it worries me that many couples leave all the navigation to the man, with the woman totally clueless as to how to get from point A to point B.

That's not to say that I advocate carrying a sextant. Ours sat in its case and was only taken out when Peter felt like exercising his brain a bit, and fortunately we never had to rely on a fix from it because to use it properly one must continually keep up one's skills in using it. I'm not sure that it's worth it. Carrying more than one GPS is a reasonable precaution. Carrying paper charts is, IMO, a necessity. Understanding the basics of navigation is most important. If you have confidence in your compass you can usually plot a DR course that will get you to land, though not necessarily the land you were planning to go to. And I'd hate to have to navigate the Pacific Ocean without electronics aids, but it's been done for thousands of years.
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Old 02-11-2007, 08:39 AM   #13
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As a woman, it worries me that many couples leave all the navigation to the man, with the woman totally clueless as to how to get from point A to point B.
Now thats funny! My WIFE is the navigator and radar expert. I have very little experience navigating. I can find my way looking at a chartplotter but thats it. Of course, I will be taking navigation classes in the near future. She is going to take a diesel engine course since that is my strong point.... RT
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Old 02-11-2007, 10:51 AM   #14
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rw, good for both of you.
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Old 02-11-2007, 01:22 PM   #15
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Where are we?

We're all here because we're not all there!

Cheers!

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Old 02-11-2007, 01:45 PM   #16
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No truer statement[V] Still counting the months and dollars...this part sucks!
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Old 02-11-2007, 02:32 PM   #17
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I qualified as a ship master before GPS was invented and so I love working with my sextant. It is a tremendous piece of kit that has been arround for a very long time. I also enjoy working out my sights using the Marc-St.Hillare method, i.e. logarithms and haversines rather than using the tables of computed azimuth and altitude.

Having said that, I think GPS is great. In the 'good old days' I remember Atlantic crossings where we saw no sun all the way. Approaching the Canadian coast was a nightmare because of Sable Island, low, engulfed in fog, poor radar echo and compared to today poor radars too. There was an RDF station but as the bearing was never particularly accurate and it was often just a degree or two on the bow it was not of great help. Sure there was LORAN, but how many European ships had that? DECCA worked fine closer to the coast but a the NE Canadian chain did not use the newer multi-pulse system one had to know one's position aaccurately to set it up.

Even the North Sea in foggy weather was a nightmare. Approaching the Thames from the North with all the sandbanks of England's east coast was a nightmare compounded by strong tides There are many examples of navigation made easier by GPS and I am all for it! Generally, it has also made it safer.

However, GPS is only an aid to navigation. It is not infallable and has to be checked against dead reckoning and other methods of fixing the ship.

One often hears, "what will happen if you lose power". My answer to that is how do you navigate with a sextant if you lose power. You need to know the time very accurately, with the exception of establishing latitude by meridian altitude. No idea at all to take stars without knowing the time. The moon you can forget too as it is so close its GP (geographical position) changes so rapidly that the exact time must be known. Morning and afternoon sun sights still require an accurate time if your position line wil not be out. So where do we get our accurate time signals from if the power is down? How many boats carry chronometers and of those how many navigators bother hemselves to rate the chronometes?

Let's move on folks. This is the 21st centuary and I am all for GPS used wisely. If you fall for the sextant back up argument, then be aware just how much kit you need. Sextant, rated chronometer(s), time signals, almanac, tables of computed altitude and azimuth (or equivilent Air Navigation Tables) or Norries Nautical Tables (or equivilent).

One final point on the sextant issue. Do I use my sextant? Yes. Where do I get the accurate time from? The GPS! And here is the interesting thing. Even if the GPS signals are out due to solar activity, the time signal will still be correct!

An on more point regarding navigation in general. I would say that most mistakes in navigation were made in plotting the position onto the chart. Irrespective if the position was obtained from sights, DF bearings, bearings and ranges, DECCA, LORAN, SINNS, CONSOL or OMEGA the actual plotting process was where misstakes crept in. The use of plotters or electronic charting removes that source of error. Sure, you should keep a plot on a paper chart but if you have a plotter or use digital charts on a computer then you can see immediately if your plot on the paper chart differs from the digital plot.

Aye

Stephen

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Old 02-11-2007, 03:32 PM   #18
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Just to agree with JeanneP, Nausikaa, and others, I carry a second hand held GPS and insist on updating paper charts - and even keep a paper log with position, heading, and wind information (just in case.) As an electrical engineer you would think I would trust the electronics - But I don't.

In March 2003 I was crossing from the Galapagos to the Marquessas (a very lonely stretch of water) listening to the invasion of Iraq on the SSB and wondering if the US military would shut down the GPS system as a defensive measure. We had no sextant on board, no HO-249, and no Nautical almanac, but since it was march and we were so close to the equator we built a sextant (from a bit of board and a fishing weight) and figured if the worst happened we could work out a sun sight with a calculator and a clock.

Thankfully the GPS system never shut down (and we never really had to use our improvised sextant) but it could have become pretty harrowing had it been, and if we had nothing to fall back on...
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Old 02-11-2007, 03:35 PM   #19
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Aye Nausika!

Obviously you are a far wiser salt than I could ever hope to be and my minimal talents with my sextant are purely for entertainment and mental exercise while sailing. I am purely a beginner with it and still get a rush when I correctly find my GPS position. Even so, I still fully rely on the software to perform all the calculations. As such, I rely on my laptop and wireless GPS signal to provide the correct time. The only tools I need then are my sextant, laptop & software, battery and a reasonably fresh time signal. The chipset clock does a pretty darn good job of tracking time once given an accurate Zulu.

I would hope that newer generations of sailors will continue to keep the Old School methods alive in whatever technically aided form possible. Every time I stand on deck at twilight and try to align the sky with my star finder plot, Iím always amazed by the fact that this was the norm of navigation for many centuries. Captains of old were some truly capable humans.
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Old 02-11-2007, 05:44 PM   #20
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Before Harrisson invented his chronometer the best navigators could do was establish latitude with accuracy. They used to sail to a predetirmined latitude and then cross the ocean at that latitude. Paralel sailing. After Harrisso came up with his invention mariners were able to establish longitude with some degree of accuracy.

When I was a cadet and junior officer we used to carry three chronometers and rate them daily against radio times signals. Why three? Because if one went south the other two, when corrected for chronometer error, would still be showing the same time. If we only carried two and one went south, how would we know which was wrong?

There is however a method of establishing longitude without using a chronometer. It is called lunar distances. Old Joshua Slocum was a master at lunar distances so when he wrote that he "boiled his clock" he was playing a bit of a joke on most of his readers who knew nothing about lunar distances. The method was very complicated, cumbersome and time consuming......but it worked. And as we know, Slocum didn't get lost (except once just out of the Staraits of Magellan but that had nothing to do with taking sights)Unfortunately, the tables needed to work out lunar distances dissapeared from nautical almanacs long ago.

I am impressed at Dave making a sextant. Not an easy task. Old navigators used what was caled a back-staff which, although far less accurate than a sextant, was easier to make. After the back-staff came the astralobe then the octant and finally the sextant as we know it.

Taking sights from the deck of a small boat isn't easy. In fact, taking sights from a large ship can be difficult at times. The ship / boat's motion and the lack of a good horizon create problems. Aur navigators solved the horizon problem by using a buble sextant. I believe that a German company even produced buble attachments for their marine sextants.

Another interesing thing is that when navigating in ice we had no real horizon so what we used to do was to fil a bowl with mercury and superimpose the true sun on the reflected sun in the mercury. The angle was then double the normal sextant altitude and so had to be halved but obviously did not need to be corrected for dip.

All this is intereting from an historical point of view and I too hope that the old methods are kept alive both for their own sake and as a back up if things go wrong but there is no point in ignoring new technology which in more case than not has made navigation easier, simpler and more accurate.

Having said that, the rush one gets after having taken a ship or boat accross an ocean using nothing but the sun and the stars and having the landfall turn up exactly as predicted has to be experienced to be believed. I still feel like shouting "eureeka" whan it happens - just don't ask me to run naked from the bath tub as old Archimedes did of yore.

Aye,

Stephen

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