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**boatman61** · 10-05-2016, 17:05

Quote:

Originally Posted by iyamwhatiyam

I was enlightened by reading "How to Read A Nautical Chart" by Nigel Calder. In the first section, The Limits of Accuracy, I came to know something I had never thought about. The electronic chart comes from one place and the GPS position from another!!! Thus you can be in the sea and show up on dry land on your plotter, or worse, visa versa.

Yup... going up the Kanakale to the Sea of Marmaris my laptop plotter showed me travelling along a ridge 1km inland.. have had these kind of errors a few times in various parts of the world..

TooCoys · 11-05-2016, 01:02

Quote:

Originally Posted by AnglaisInHull

So I'm curious what the more experienced among you think. Is the same phenomenon happening in sailing? How do you balance the use of the technology with the need to be aware of your physical surroundings? Or is it just such a different environment that it's not an issue?

I have never cruised, and this is my first post, so I can't speak to the sailing issue.

However, I am a 911 operator and police dispatcher, and I cannot tell you how many calls I've dispatched over the last few years of vehicles traveling the wrong way on a one way access road, or even the freeways themselves.

And if they aren't killed first, the drivers excuse is always the same. "I went where the GPS told me to."

Sandero · 11-05-2016, 02:33

Quote:

Originally Posted by TooCoys

I have never cruised, and this is my first post, so I can't speak to the sailing issue.

However, I am a 911 operator and police dispatcher, and I cannot tell you how many calls I've dispatched over the last few years of vehicles traveling the wrong way on a one way access road, or even the freeways themselves.

And if they aren't killed first, the drivers excuse is always the same. "I went where the GPS told me to."

Auto navigation seems to be kind of inaccurate. I notice it when I choose to follow my own "route" and the thing hasn't figure out for some time that I have left its prescribed route... and is repeating the last "guidance instruction". I don't doubt that if you were driving on the wrong side of a divided highway or 2 way street against traffic it would not "know". I suspect this is part of the algorithm / database / precision.

Pelagic · 11-05-2016, 03:10

Quote:

Originally Posted by TooCoys

I have never cruised, and this is my first post, so I can't speak to the sailing issue.

However, I am a 911 operator and police dispatcher, and I cannot tell you how many calls I've dispatched over the last few years of vehicles traveling the wrong way on a one way access road, or even the freeways themselves.

And if they aren't killed first, the drivers excuse is always the same. "I went where the GPS told me to."

Welcome to CF and great first post.... I think that really underlines the danger of depending on only one reference tool as well as the Darwin theory.

bletso · 11-05-2016, 03:30

Quote:

Originally Posted by rsailorbob

Gps is a thousand times more accurate than navigating manually. If you have a chart plotter, a tablet, and a phone, you have three layers of redundancy. Keep a log so you always know where you were an hour ago. Have a paper chart and situational awareness. You need to know the navigational hazards and restricted areas. No worries, we are navigating at 6 knots.

Actually, you don't have three layers of redundancy as it all depends on the GPS in the first, second and last place! It is at best a very good illusion. So, definitely keep an accurate DR plot on a paper chart, just in case Murphy decides to visit you.
No worries??, hell I can ground at 4 knots and not be able to kedge off. It all depends on too many factors. It is blatantly obvious that many people have no situational awareness and that was before GPS!

I don't trust it inclusively. Just the other day it told me my destination was on my right, yea, right. My destination was actually a 1/2 mile further down the road. (Yes, I stopped and ask a real person!) Still it has got me un-lost a few times. I hate cities and much prefer the water, well most times anyway.

Gadagirl · 11-05-2016, 17:52

Here is an interesting podcast that expands on the OP. An interview of
Greg Milner
Greg Milner is the author of Pinpoint: How GPS Is Changing Technology, Culture and Our Minds (Norton, 2016). His writing has appeared in the New York Times, Slate, Wired, and other publications. He’s based in Brooklyn, New York.

It's very interesting.
Recalculating the Global Influence of GPS - Science Friday

RaymondR · 11-05-2016, 23:32

Quote:

Originally Posted by Catapault

Absolutely.

If a chart isn't surveyed to WGS-84, you MUST adjust any point you put on it from a GPS. All modern charts include this correction information of course, and many have already been adjusted to it. (And yes, it can get way more complicated than that if you start looking at proper geodetic datum conversions !)

One would hope that all Electronic charts have been for sure. But I know this isn't always so.

Also, any number of locations were last surveyed before GPS was invented and in common use. Just because the numbers line up, dosn't mean it was surveyed correctly in the first place.

For a little blue marble fairly covered by satellites, this planet of ours isn't mapped nearly as well as some people think it is..

I was crossing northern Australia a couple of decades ago and found a waypoint where the DTW was still about 1.5 miles with a beach a few cables away. When I read the small print I found the chart was based on a survey by Mathew Flinders at about the time of the Napoleonic wars. Fortunately there are modern charts available for this area these days.

Unfortunately Australia is cursed with multiple layers of bureaucrats each with there own turf which they jealously defend and the modern electronic charts which are available are not free as they are in many countries. So whilst one level of these folks impose all sorts of rules upon us, supposedly to keep us safe, and fine us if caught breaking them, another will not freely provide one of the best tools available to do so.

**JPA Cate** · 12-05-2016, 01:13

^^^^do not expect perfection from imperfect bureaucracies....... Sorry..

Ann

PS. Valhalla,

We did a lot of sextant navigation in the days gone by. Few accidents, because, we knew the positions were plus or minus 5 miles at best, and allowed clearances accordingly. It was not point to point, but way more amorphous, and always allowing a lot of margin, especially as DR's extended. I actually think it would have been safer, in that the computer assisted groundings we have seen the last 15-20 yrs. or so, would easily have been avoided, because we would have been on eyeball navigation, not GPS...which is only as good as the charts from which it is taken. [The position being close to right, but the graphic being off.]

Ann

Robin3 · 12-05-2016, 04:52

That Captain Cook has got a lot to answer for with his darned innacuracies

RaymondR · 12-05-2016, 13:39

Quote:

Originally Posted by Ann T. Cate

^^^^do not expect perfection from imperfect bureaucracies....... Sorry..

Ann

I can live with the imperfections, it's the robber baron exploitiveness I have problems with.

RaymondR · 12-05-2016, 13:43

Quote:

Originally Posted by Robin3

That Captain Cook has got a lot to answer for with his darned innacuracies

I'm a big fan of Capn Jimmy, I am sure that if someone had offered him a GPS he'd have snatched it out of their hands and hugged them (maybe even hugged and kissed them).

Robin3 · 12-05-2016, 15:06

Quote:

Originally Posted by Ann T. Cate

^^^^do not expect perfection from imperfect bureaucracies....... Sorry..

Ann

PS. Valhalla,

We did a lot of sextant navigation in the days gone by. Few accidents, because, we knew the positions were plus or minus 5 miles at best, and allowed clearances accordingly. It was not point to point, but way more amorphous, and always allowing a lot of margin, especially as DR's extended. I actually think it would have been safer, in that the computer assisted groundings we have seen the last 15-20 yrs. or so, would easily have been avoided, because we would have been on eyeball navigation, not GPS...which is only as good as the charts from which it is taken. [The position being close to right, but the graphic being off.]

Ann

That is the true beauty of being brung up properly! Now the modern stuff is very nice AND as a result you can make better use of it than someone with the modern day smart phonist upbringing ever will.