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Thread: The danger of GPS as the sole means of navigation. Reply to Thread
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  Topic Review (Newest First)
02-14-2016 12:57 PM
colemj
Re: The danger of GPS as the sole means of navigation.

Ah, got it now. I've read the other thread but thought you were pointing to a different discussion. Thanks.

Mark
02-14-2016 12:37 PM
boathooked
Re: The danger of GPS as the sole means of navigation.

Colemj, there is a discussion thread about my link already. I was simply pointing out that this ruling was interesting given this threads discussion. It seems that it is good enough for professional mariners to navigate solely by GPS, only requiring a second GPS device.
02-14-2016 10:04 AM
colemj
Re: The danger of GPS as the sole means of navigation.

That link just seems to be the basic news article. Is there a discussion on it that I am missing?

Mark
02-13-2016 08:42 PM
boathooked
Re: The danger of GPS as the sole means of navigation.

Interesting discussion based on the latest from the USCG....
https://gcaptain.com/u-s-coast-guard...ctronic-charts
02-12-2016 05:59 PM
knuterikt
Re: The danger of GPS as the sole means of navigation.

Quote:
Originally Posted by killarney_sailor View Post
Guys, lets all talk about the same thing at the same time. A GPS gives you an absolute position (lat/lon) while a chart plotter gives you a relative position (where you are in relation to stuff on the earth's surface). In the pre-electronic world a sextant gave a (fairly inaccurate) absolute position while a paper chart with a sextant position or compass-derived fix gave relative location. Most of the discussion here has been about the shortcomings of chart plotters and the charts they use rather than about GPS. The GPS system has done a remarkable and reliable job, for a few decades, of telling us where we are located. In general chart plotters work, but the charts that are used could be improved - sometimes quite a bit.

GPS could be affected by lightning, but I have two GPS units that are not connected to the boats electrical system. I have two electronic navigation systems with one not connected to the electrical system. In an electrical storm we put our iPad which has Navionics charts in the Faraday cage (otherwise known as the microwave). I will take my chances. And before anyone says I don't appreciate the good old ways of doing things, I have sailed offshore using a sextant and have taught math so the numbers do not bother me. It is a really sad thing to have to rely on. Just when you are approaching a landfall it always seems to be overcast.

I also agree with Mark about the cost of paper charts if you intend to sail long distances. I bought a package of 120 charts of the Pacific and still did not have all the charts. I think I looked at three of the ever. One was for Pitcairn and it even said the position of the island on the chart was wrong. My no one has fixed it rather than adding the error note I have no idea.
In short there are several factors that can result in navigation errors putting the you on a rock.

GPS
- Loss of power and equipment failure
- Inaccuracy in position caused by natural radio disturbance (solar activity, local conditions)
- man made radio interference jamming and other sources

Charts
Inaccuracy in charts caused by
- Feature placeed in wrong position
- Features placed wrong in relation to other features.
- Uncharted objects (rocks)
faeatures lost/hidden by human error or software error.
I have seen paper charts recalled due to errors introduced in production, same type of errors have been seen in electronic charts.

When navigating within visibility of land it would be unwise to rely solely on the boat icon in the chart. Using landmarks and ATONs in combination with GPS position is the best way IMHO.

My main charts are vector charts but I do know that the charts I use are of good quality and know how my plotter works.

In the waters I sail you want the charts at hand, my plotter is fixed and won't blow away from the cockpit.

But I also carry paper charts in 1:50000 or even better,just in case.
02-12-2016 05:18 PM
killarney_sailor
Re: The danger of GPS as the sole means of navigation.

Guys, lets all talk about the same thing at the same time. A GPS gives you an absolute position (lat/lon) while a chart plotter gives you a relative position (where you are in relation to stuff on the earth's surface). In the pre-electronic world a sextant gave a (fairly inaccurate) absolute position while a paper chart with a sextant position or compass-derived fix gave relative location. Most of the discussion here has been about the shortcomings of chart plotters and the charts they use rather than about GPS. The GPS system has done a remarkable and reliable job, for a few decades, of telling us where we are located. In general chart plotters work, but the charts that are used could be improved - sometimes quite a bit.

GPS could be affected by lightning, but I have two GPS units that are not connected to the boats electrical system. I have two electronic navigation systems with one not connected to the electrical system. In an electrical storm we put our iPad which has Navionics charts in the Faraday cage (otherwise known as the microwave). I will take my chances. And before anyone says I don't appreciate the good old ways of doing things, I have sailed offshore using a sextant and have taught math so the numbers do not bother me. It is a really sad thing to have to rely on. Just when you are approaching a landfall it always seems to be overcast.

I also agree with Mark about the cost of paper charts if you intend to sail long distances. I bought a package of 120 charts of the Pacific and still did not have all the charts. I think I looked at three of the ever. One was for Pitcairn and it even said the position of the island on the chart was wrong. My no one has fixed it rather than adding the error note I have no idea.
02-12-2016 04:55 PM
knuterikt
Re: The danger of GPS as the sole means of navigation.

Quote:
Originally Posted by jackdale View Post
Look at the charts included in the link

Navigating With GPS, Charts, and Eyeballs
The charts with GPS tracks in that article is used to document the inaccuracies in the different charts.
That does not prove that GPS is accurate does it?

I don't question the other points made in that article.

But you quoted one important wrong statement in that article as important.
My point is even if you follow your own GPS track it might bring you onto stuff you don't want to hit.
02-12-2016 04:38 PM
tdw
Re: The danger of GPS as the sole means of navigation.

Quote:
Originally Posted by SVAuspicious View Post
Exactly. It is quite hard to miss a continent. *grin* I am often pleased to find the mouth of the Chesapeake Bay but am never concerned about losing North America.

On the other hand seeing a tiny island climb above the horizon exactly where it is expected, regardless of electronic navigation, never ceases to cause me wonder.

Using celestial I'm just happy to be able to see the bloody island at all.
Dave,
I thoroughly agree. Being able to find your position using the sun and the stars is a fine skill and the satisfaction it brings makes it well worthwhile. Likewise (to some extent) I always row our rigid dinghy, simply because I enjoy it. Nonetheless if I had to ditch either GPS or Sextant I'm afraid that the former will win out.
02-12-2016 04:38 PM
jackdale
Re: The danger of GPS as the sole means of navigation.

Quote:
Originally Posted by knuterikt View Post
But it's wrong
A GPS is accurate in perfect conditions with waas/egnos and perfect radio signals.
There is a reason NOAA issue space weather forecasts.
Local conditions can also affect the accuracy.

Read more here Space Weather and GPS Systems | NOAA / NWS Space Weather Prediction Center
Look at the charts included in the link

Navigating With GPS, Charts, and Eyeballs
02-12-2016 04:30 PM
skygazer
Re: The danger of GPS as the sole means of navigation.

Quote:
Originally Posted by knuterikt View Post
...There is a reason NOAA issue space weather forecasts.
Local conditions can also affect the accuracy.

Read more here Space Weather and GPS Systems | NOAA / NWS Space Weather Prediction Center
Reliable source and great information. I was struck by one statement about ionospheric scintallations that are not caused by storms:

Quote:
The instabilities are most severe just after sunset...
May help explain this troubling experience I had:

Quote:
Originally Posted by skygazer View Post
...one time I'd sailed all day and was tired and coming to an anchorage behind three islands. I wanted to cut between two islands as the sun had set. My chart lacked enough info so I zoomed in with my GPS hoping for more depth detail. To my horror it showed that I was already past all three islands. This was a total glitch, and never happened again but taught me to be very wary. Yes, I took the long way around and skirted all three islands.
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