The danger of GPS as the sole means of navigation. - Page 3 - SailNet Community
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post #21 of 110 Old 09-02-2013
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Re: The danger of GPS as the sole means of navigation.

No Polish jokes, please...

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"The ship was using an unapproved electronic chart plotter, which is a bit like your GPS for the car.

"The Danio, from the time he sailed from Perth to the time he went aground, had two positions on his chart... he was relying solely on his GPS.

"They [the crew] basically said 'we'll draw a line and we'll go the quickest way possible' without really thinking about 'do I need to go that close to the Farne Islands?'"

BBC News - Farne Islands grounded ship: MV Danio's lookout 'asleep'

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post #22 of 110 Old 11-25-2015
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Re: The danger of GPS as the sole means of navigation.

Talk about heads down in the cockpit, not having "situational awareness". Midday, 10 kilometer visibility. Occasional cumulus. Sea state 2 maybe? We're leaving Falmouth Harbour, Antigua. There is a dog leg to port leaving harbour. There is a large reef to port, with the waves breaking it was inherently obvious to even the most casual observer that there be very shallow water, with rockses. That's plural for rock. Guy sailing in from offshore, oblivious to a) the buoy and b) the aforementioned rockses. So we have about 5 people up on foredeck waving and yelling, even try hailing on the radio. They are on a straight line from the mouth direct to the yacht club dock. All of a sudden you see the head jerk up from the comfort of the display and he has an "oh, #$%^" moment, drops the anchor, starts spinning around, but thankfully he didn't hit the rocks. One of the local crew observes that it is a common occurrence, people plot the waypoint direct to the yacht club, unfortunately forgetting about the rockses. Or the Buoy. Use the eyeball. Even with my glaucoma, astigmatism and near-sightedness, I could still see the hazard with my glasses off. And I hope I never have the experience of making this mistake myself.
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post #23 of 110 Old 12-18-2015
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Re: The danger of GPS as the sole means of navigation.

The ASA 105 class is a great start to learn charts and it is home based...

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post #24 of 110 Old 01-24-2016
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WARNING: Careful if you have just turned on your GPS

I recently learned something scary about GPS. Don't just turn it on and believe the position it shows. It may have been a tech glitch, but I think it is something that commonly happens. Could be very serious on the water.

I've been learning celestial navigation at home. After quite a bit of study I did my first sun sights with my new sextant, land based, mid morning and mid afternoon shots. I'm far enough north that at that time (Christmas) the sun was very low, not the best for accuracy. I figured being a newbie if I could place myself in New England rather than Africa I'd be pretty happy. I then did my sight reductions and plotted my position.

I decided to check just how close I was to my actual position by putting my GPS where I'd taken the sights and turning it on. I left it for a bit to boot up and acquire 7 or 8 satellites. When I tried to get latitude and longitude I couldn't find it in the menu, just the chart (map here on land) and the speed and direction screens that I normally use.

After quite awhile (I'll estimate 15 minutes from turn on to numbers) I found the hidden menu and wrote down the exact latitude and longitude, then went inside and plotted it on the same plotting sheet as my sextant location (two LOPS crossing).

I was pleased to find I was only a few miles off. Just out of curiosity I googled my latitude and longitude, then plotted google's numbers on the same sheet. I was only 1/2 mile off!!!

I'd forgotten I'd left the GPS out there. Two hours later I saw it and the numbers had changed. It now agreed with google.

My sextant gave me a more exact location than my GPS!!! I attribute this to it taking time for the GPS to continually check and average readings from all the satellites. Or maybe just a glitch somewhere in the tech chain.

Perhaps it is well known that your GPS must be on for a long time to be accurate, but I did not know that. I thought when it gave an answer it was correct. I have now learned that GPS will always give you an exact location, even if it is wrong! Thinking about our aging satellites, our poor economy reducing our ability to upgrade them in a timely fashion, radiation and solar storms, computer glitches, etc. I intend to be even less certain about GPS positioning. Not to mention EMP weapons and cyber hacking. I've read that the Navy is going back to teaching celestial navigation because you can't hack the moon and stars.

I'm now inspired to go beyond being a celestial nav "trained monkey" and get a deeper understanding which will help with greater accuracy. Doing a land sight is inherently more accurate than bouncing around in a small boat. However, even a trained monkey can do quite well, and it is quite interesting and excellent exercise for one's brain. My own brain felt rusty and moribund when I started, but yes, an old dog can learn new tricks.

Last edited by skygazer; 01-24-2016 at 09:16 AM.
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post #25 of 110 Old 01-24-2016
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Re: The danger of GPS as the sole means of navigation.

If your GPS has not been turned on for quite a while, or if it had been moved to a different location while off, it can take 20-60 minutes to download the current almanac data for it. Until then, it will be using old assumptions and can be in error.

This is not the fault of the GPS, nor is it a problem. Understanding how a tool works is as important for the GPS as it is for the sextant.

Mark
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post #26 of 110 Old 01-24-2016
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Re: The danger of GPS as the sole means of navigation.

Another common mistake, when reading lat/long off a gps is whether you are reading your present position or the position of the cursor. The difference can be deceiving on many devices. You press find ship or other button and it resets the data field to present position.

I was in radio contact with a buddy on my way out to the islands and asked him where he was. We were planning to rendezvous underway. He gave me his lat/long. When I checked my chart, he claimed he was 10 miles inland! It was his cursor.


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post #27 of 110 Old 01-24-2016
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This isn't actually true, but funny and relevant.

A real example of the eRumor as it has appeared on the Internet:

Summary of eRumor:
This story says it is based on an actual radio conversation between the U.S. Navy Aircraft carrier the U.S.S. Abraham Lincoln and a Canadian Lighthouse. The carrier and the lighthouse keep radioing each other to give way thinking each is a ship, until the game is over when one of them identifies itself as a lighthouse.

This is based on an actual radio conversation between a U.S. Navy aircraft carrier (U.S.S. Abraham Lincoln) and Canadian authorities off the coast of Newfoundland in October, 1995. (The radio conversation was released by the Chief of Naval Operations on 10/10/95 authorized by the Freedom of Information Act.)

Canadians: Please divert your course 15 degrees to the South to avoid collision.

Americans: Recommend you divert your course 15 degrees to the North to avoid a collision.

Canadians: Negative. You will have to divert your course 15 degrees to the South to avoid a collision.

Americans: This is the Captain of a US Navy ship. I say again, divert YOUR course.

Canadians: No, I say again, you divert YOUR course.

Americans: THIS IS THE AIRCRAFT CARRIER USS LINCOLN, THE SECOND LARGEST SHIP IN THE UNITED STATES? ATLANTIC FLEET. WE ARE ACCOMPANIED BY THREE DESTROYERS, THREE CRUISERS AND NUMEROUS SUPPORT VESSELS. I DEMAND THAT YOU CHANGE YOUR COURSE 15 DEGREES NORTH?I SAY AGAIN, THAT?S ONE FIVE DEGREES NORTH?OR COUNTER-MEASURES WILL BE UNDERTAKEN TO ENSURE THE SAFETY OF THIS SHIP.

Canadians: This is a lighthouse. Your call.
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post #28 of 110 Old 01-24-2016
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Re: The danger of GPS as the sole means of navigation.

Every boat should have a copy of this guide on board"

http://www.nauticalcharts.noaa.gov/m...1/ChartNo1.pdf

Even if you think you already know everything about charts. I make a point of taking it out every year and review it. It is for paper and electronic charts.
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post #29 of 110 Old 01-24-2016
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Re: The danger of GPS as the sole means of navigation.

I recently helped a couple take their boat near offshore down the coast from Washington state to California. They were experienced sailors on lakes and Puget Sound waters but had never had to navigate by GPS nor communicate with others as far as reporting position. The skipper was not aware that you can give lat/lon in degrees/minutes/seconds or degrees/minutes with minutes in decimal to three places right of the decimal point. He wanted to be the one to report our position to the radio net we were checking in with twice a day. There was a period of confusion when he was giving lat/lon in minutes.decimals and the radio net lead was expressing confusion. It took a great deal of explanation to clear it up. Not anything dangerous in this situation but it could have been. And it would have been hopeless for the skipper to find his position on a chart should he need to do that. He insisted that he was giving minutes/seconds when it was decimal: e.g. 48 degrees 10 minutes 781 seconds north. It is not possible to have 781 seconds. He also did not understand that he could set his GPS or chartplotter to give lat/lon in either notation.

Everyone that goes out should either take a formal course or do some significant studying of charting, navigation, and using navigation equipment. Just having a GPS will not necessarily save you from getting lost or making a critical mistake.
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post #30 of 110 Old 01-24-2016
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Re: The danger of GPS as the sole means of navigation.

Hey,

Not to belabor the point, but if my GPS is accurate to within 1/2 a mile, I'm ok with that. I rely on navigation aids to REALLY let me know where I am.

Barry

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Mt. Sinai, NY

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