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Old 05-01-2015, 18:04   #46
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Re: Another foundering how do chart plotters get it wrong

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Originally Posted by aitch View Post
Transmitters an is right. We don't know exactly what happened, but there are some things we do know.
The yacht foundered on Gull Island, just of the coast of Cape Barren Island on the East Coast of Tasmania. It was 5 am, and therefore NOT fully dark. It was returning to Melbourne with an experienced crew, having just won the difficult and arduous Melbourne to Hobart race, via the west coast. It is a well performed vessel, not new to this area.
The strictures of ORCV ocean racing would have caused them to have redundant navigation and radio systems, including paper charts and instruments for postion fixing in the event of electronic failure.
Surveys in this part of Australia are recent and accurate.
They chose to go to the east of Flinders Island, a route which I have sailed on my own yacht. Conditions at the time (it is now summer) were not particularly difficult.
We do not know what happened, but blaming charts or chart plotters is not the way to go.
The question was not about that particular vessel, though it's clearly a case of human error. My question was specifically about chart plotters and charts. I just introduced the topic using that as an example.

A few years ago a well known yacht in the Three Peaks Race also ran aground on sand, which if I recall was due to following their chart plotter.

Most of the charts around this area are not from Captain Cook era, though there are clearly marked 'not surveyed' zones still.

From what I'm picking up on this thread the reason is usually firstly a failure to keep a look out, and when it gets down to charts and plotters, I'm picking up that the GPS locations received are accurate, but not necessarily where the plotters then locate these on a chart.

? Have I got this right.

For those who have asked, Gull Island is on the East Coast of Flinders which is on the North East Coast of Tasmania. It's clearly marked on charts. However, there is a low lying reef on the 'east' side of Gull Island. But that's clearly marked too.
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Old 05-01-2015, 18:07   #47
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Re: Another foundering how do chart plotters get it wrong

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Originally Posted by Rustic Charm View Post
From what I'm picking up on this thread the reason is usually firstly a failure to keep a look out, and when it gets down to charts and plotters, I'm picking up that the GPS locations received are accurate, but not necessarily where the plotters then locate these on a chart.

? Have I got this right.
Almost. The GPS positions received are accurate, and the plotter accurately plots these on the charts.

The pictures of the hard bits and other stuff on the chart may not be in the correct places, though.

Mark
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Old 05-01-2015, 18:13   #48
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Re: Another foundering how do chart plotters get it wrong

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Captain Cook may have been on the Rum the night before he charts a reef
Ridiculous. The professionals that drew these charts with incredible patience and skill are not much appreciated here! But they didn't have a $20 gps so that makes em stoopid, eh?
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Old 05-01-2015, 18:17   #49
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Re: Another foundering how do chart plotters get it wrong

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The problem with "crowdsourcing" data is that half of the "crowd" is below average intelligence. You only have to read active captain to realize this.
I have to disagree with this. Statistically, if half the crowd is below average intelligence, the average goes down.

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Old 05-01-2015, 18:40   #50
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Re: Another foundering how do chart plotters get it wrong

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I have to disagree with this. Statistically, if half the crowd is below average intelligence, the average goes down.

goat (happily lowering the bar)
Sorry for the thread drift
I never really did understand statistics but am I to understand that if half the crowd is above average intelligence, the average goes up?
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Old 05-01-2015, 18:53   #51
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Re: Another foundering how do chart plotters get it wrong

I have trouble getting a sense of my surroundings on most plotters. It feels a bit like driving down the hiway with blinders on so you can only see a narrow path ahead. It's hard to anticipate, look for, and worry about something that you don't know is there at all. Then there's also the clarity of the pixels/screen. Most charts give me a sense of what to look for, like:
"ahh.. look up there 20 miles... theres a shallow spot reported",
or..
"we'd better think about if we want to go thru that narrow channel 5 miles up in this heavy cross wind and sea state"...
I guess I'm saying with a big chart your eyes look for things, with a mini screen you have to scroll around... and lose track...

I'm not anti plotter, but I think people take them as gospel. I'd feel a lot better if I had a 36" Hi Def screen :>)
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Old 05-01-2015, 19:04   #52
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Re: Another foundering how do chart plotters get it wrong

Hey Boatman.......you and Mark J are really doin good......i had to give up my Mk 1 eye balls for the Mk 1 Mod 2 Eyeball,,,getting older.....but they still work good.

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Old 05-01-2015, 19:06   #53
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Re: Another foundering how do chart plotters get it wrong

By the way, it was Bill Clinton who ended the GPS degrading, not Jimmy Carter.

If they hit Gull Island or the rocks to the east of it, they were cutting it very fine going around Cape Barron Island as this is only 500 metres offshore.
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Old 05-01-2015, 19:25   #54
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Re: Another foundering how do chart plotters get it wrong

"2 Chart plotter electronic maps are accurate copies of paper charts."
Actually, not in the US and not in any modern cartography department. Electronic maps may be rendered directly form a digital information file. If they are copied from charts, they would be copied from acetate or other "plastic" media which is dimensionally stable, because...
" 3 Paper Charts are inherently inaccurate. "
Yes, paper is dimensionally unstable and the lithography process introduces even more instability. A paper chart that has been folded and refolded, stretches or shrinks because of the folds. Distances are no longer accurate. In addition, as the paper stock is pulled through the printing press--which is quite similar to a laundry machine called a "mangler"--the paper may be stretched. So paper charts are known to have certain limits. I discussed this with one chart printer many years ago, complaining that a mountain lean to shelter was shown on the wrong side of a creek. They said that's easy, the blue plate was simply a little out of alignment during the printing process, possibly because of paper stretch, and that there were limits imposed by the process, even before folding and storage and use distorted the whole chart.


By and large this is all trivial compared to the errors in datums, errors in survey, and errors in navigation. Which apply to all forms of charting and cartography, digital, paper, or other media.
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Old 05-01-2015, 23:41   #55
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Re: Another foundering how do chart plotters get it wrong

In my opinion in this case near Gull Island it was human error.
As to the OP most of my boating has been done on the Qld coast and the Barrier Reef.
Many years spent with charts only scratching around reefs etc off Nth Qld with eyes peeled on the water after consultation with the charts.Personally I am now much more comfortable on the water with the electronic aids available to me as opposed to just charts.
My personal observation of the electronic charts and GPS units is that they are rarely more than metres in error be it signal or chart fault.
I certainly am not able to compete with that by paper charts alone.
Frankly I am continually amazed at their acuracy especially relative to sand banks,reefs and channel markers etc I am personally very familiar with.
Although we own one more boat than I need we still charter a bit and the management of that company continue to tell me that most of the groundings of their boats happen due to complacency of experienced skippers.
Chris
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Old 06-01-2015, 00:35   #56
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Re: Another foundering how do chart plotters get it wrong

I've posted this somewhere before on a similar thread, but here goes.

1 - Most charts in the western world were surveyed in the 1800's (US and Europe). Some have been updated since then, but the ones that have been updated tend to be the ones that the merchant marine traffic uses.

2- When the waters were surveyed, here is how it was done. A boat would be rowed in a DR straight line while casting the lead and the results noted (depending on the depth, the lead might have had as much as 10 or 20 meters between each cast). What the bottom was like or its depth between the casts was interpolated, the surveyors did not know.

3- The boat was then moved about 100 meters (yards) to one side and the process repeated. What the bottom was like, rocks etc or the depth, was interpolated - the surveyors did not know what the bottom was like.

4- Over the years, as boats have run aground, hit rocks etc, some of these obstacles have been noted on the charts, if they were reported. Most have not been noted, which is why you'll hear locals telling visitors "ya gotta stay pretty far out from that coast because there is a big rock not shown on the charts"

In OZ/NZ and the pacific islands, most of the charts were surveyed and drawn by Captain Coook or Lieutenant Bligh. Most have not been updated since their survey.

Far eastern waters have been charted by order of various emperors through time, but their methods have not differed significantly from the ones the europeans used.

In the US, I believe it was Jefferson who started the US government surveying and charting and the east coast was more or less finished sometime in the late 1800's.

All chart plotter charts are based on the government paper charts and surveys. No chart plotter is more accurate than a good paper chart.

If you go to a true chart shop and rummage around in the charts over the pacific islands you'll see lots where the island is drawn in and a passage is shown (with depths etc) through the reefs. Everything else around the island is white with the notation "not charted" Look further and you'll see a date fromt eh 1700 hundred and either the name Cook or Bligh.
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Old 06-01-2015, 01:03   #57
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Re: Another foundering how do chart plotters get it wrong

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Agreed Sue and Ann. A CP shows you what SHOULD be there, a Radar shows you what IS there. both to be backed up with the mk1 eyeball and some "common" sense. Don't cut corners, give the hard bits a decent clearance - use some seamanship, it's not a video game out there!
NEVER use one source of navigation data - trust, but verify!


Agreed, the radar gives a check/ backup to the the chartplotter and is particually usefull close to coastal hazards.
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Old 06-01-2015, 01:06   #58
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Re: Another foundering how do chart plotters get it wrong

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Originally Posted by Mirage Gecko View Post
In my opinion in this case near Gull Island it was human error.
As to the OP most of my boating has been done on the Qld coast and the Barrier Reef.
Many years spent with charts only scratching around reefs etc off Nth Qld with eyes peeled on the water after consultation with the charts.Personally I am now much more comfortable on the water with the electronic aids available to me as opposed to just charts.
My personal observation of the electronic charts and GPS units is that they are rarely more than metres in error be it signal or chart fault.
I certainly am not able to compete with that by paper charts alone.
Frankly I am continually amazed at their acuracy especially relative to sand banks,reefs and channel markers etc I am personally very familiar with.
Although we own one more boat than I need we still charter a bit and the management of that company continue to tell me that most of the groundings of their boats happen due to complacency of experienced skippers.
Chris
The GBR is very accurately surveyed thesedays.
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Old 06-01-2015, 01:07   #59
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Re: Another foundering how do chart plotters get it wrong

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Originally Posted by colemj View Post
Almost. The GPS positions received are accurate, and the plotter accurately plots these on the charts.

The pictures of the hard bits and other stuff on the chart may not be in the correct places, though.

Mark
got ya.

If I keep a track on a paper chart by using the gps locations off the gps, I should be right shouldn't I? As long as the chart has correct detail.
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Old 06-01-2015, 01:09   #60
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Re: Another foundering how do chart plotters get it wrong

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Hey Boatman.......you and Mark J are really doin good......i had to give up my Mk 1 eye balls for the Mk 1 Mod 2 Eyeball,,,getting older.....but they still work good.

Life is good if you Keepa Smilin.......




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I also am on my MK 2 eyeball's having had them replaced with Carl Zeiss lenses.

The best thing is I don't need reading glasses anymore.

Highly recommended.

If I recall my first camera was a handed down Carl Ziess Contax from my grandfather.
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