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Old 05-01-2015, 13:57   #31
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Re: Another foundering how do chart plotters get it wrong

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.
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Old 05-01-2015, 14:10   #32
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Re: Another foundering how do chart plotters get it wrong

It was even worse with Loran. I remember sailing one night with the idea of passing to the north of some shoals, and using the Loran to plot our course.

And, then finding out, that we had actually passed to the south of the shoals! YIKES!

Sometimes, it really is better to be lucky than good.
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Old 05-01-2015, 14:23   #33
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Re: Another foundering how do chart plotters get it wrong

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I was amazed to find out how much of the world's current nautical charts, that are currently in use, were drawn by men who have been dead for hundreds of years.
In the book In the Kingdom of Ice, they talk about the people who created maps back in the late 1800's. They drew up very highly detailed maps and charts that the explorers accepted as fact. Back then they believed that there was a Polar Sea, a body of water at the top of the earth, encircled by ice. All they had to do was find a way in.

The book was about the ill-fated trip of the USS Jeannette and all that happened to the boat and crew when they failed to find the passage. And I think there was a mention that there are still some maps and charts today that are based on those created back then.
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Old 05-01-2015, 14:25   #34
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Re: Another foundering how do chart plotters get it wrong

Aitch has given us more details of this incident and I am sure more details are yet to come. We have sailed this coast several times and it is a rugged coast. Despite using all tools. charts plotters, charts, GPS etc available, it is still the human input which is important, and the one which is most unreliable in my experience. 19 years onboard and still keeping my eyes open.
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Old 05-01-2015, 14:41   #35
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Re: Another foundering how do chart plotters get it wrong

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!
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Old 05-01-2015, 15:10   #36
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Re: Another foundering how do chart plotters get it wrong

The GPS companies generally outsource their charting, so don't blame them for the errors, but they certainly exist. I have found that they may exist on a chart of one scale but not another. Using my Garmin charts, on certain ones I can make my approach to North Sound, Virgin Gorda, accurately, and on others, presumably older, the course given takes me right through Gorda Peak, maybe a half mile off. By detailed searching through my database, I realized that the error was on a chart with a scale greater than 100,000, so any chart on this scale or greater is now disabled on my GPS. But it is an assumption than on a lesser scale all is accurate, although I have yet to find a discrepancy. Interestingly, I was zoomed in to a much smaller scale, but for some reason the Garmin default used the chart with the larger scale even though other, accurate charts were available in the database.. Yikes. I reported it to them, but they simply dismissed it with " we get our cartography from so and so, and we can't change it." Hmmmmm!!!

I generally am very watchful until I have verified the plotter at a given scale in a given place.
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Old 05-01-2015, 15:10   #37
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Re: Another foundering how do chart plotters get it wrong

Comments:

ON my copy of the relevant chart, the survey date is shown as 1970. This is before GPS was used in surveys. Absolute accuracy is not likely.

This area is subject to strong and poorly annotated tidal currents.

Besides Gull Island itself, there are at least three nearby rocks shown which are shallow enough to constitute a hazard to a yacht.

There is no particular advantage to a course set close to these hazards.

Query: What the hell were they doing there at dawn?

Jim
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Old 05-01-2015, 15:48   #38
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Re: Another foundering how do chart plotters get it wrong

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....... While you are at it, you might suggest that NOAA figure out some way to crowd source its data. ..............
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.
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Old 05-01-2015, 15:55   #39
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Re: Another foundering how do chart plotters get it wrong

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Originally Posted by Jim Cate View Post
Comments:

........

Query: What the hell were they doing there at dawn?

Jim
Mate, what's the problem, they had a chartplotter didn't they....


And it was prolly the shortest way home
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Old 05-01-2015, 16:36   #40
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Re: Another foundering how do chart plotters get it wrong

My friend that works for DOD reminds me that your GPS can have up to a 10% variation on your location at any given time. Not everybody uses it for a good purpose.
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Old 05-01-2015, 16:47   #41
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Re: Another foundering how do chart plotters get it wrong

"your GPS can have up to a 10% variation on your location at any given time."
Your friend may have los something in translation. While the civilian signal MAY be degraded, IIRC it was Jimmy Carter who ordered that the intentional signal degradation be stopped, and it would take a similar presidential order or other directive "from the top" before any degradation was introduced to the system as a whole.


Extremely unlikely that the US government would degrade the signal over some godforsaken rock halfway around the world.

And "10%" ?? is definitely a translation error. The folks who run it, just don't talk about it that way. 10% without saying 10% of WHAT, is gibberish.
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Old 05-01-2015, 16:50   #42
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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
Hi guys,

This morning there's been yet another grounding and loss of a sail boat in Tasmania. It's hit an island (I think) in the dark.

My question is, how does this happen? In relation to chart plotters.

Assuming they were following a chart plotter and not recording where they were on a map, how do experienced sailers like Vetus for example get it so wrong?

Are the c-ordinates coming from satalites wrong or are the chart plotters themselves misinterpreting the data?
THE TWO MOST DANGEROUS ITEMS TO BRING ONBOARD ARE ARRIVAL SCHEDULES....
AND PAPER CHARTS.
FACTS
1 GPS position is always accurate at sea to within a few meters.
2 Chart plotter electronic maps are accurate copies of paper charts.
3 Paper Charts are inherently inaccurate. Sextents are wonderful things and Captain Cook was an amazing navigator. On a good day however he could be inaccurate by 1 NM or more. Therefore electronic charts WILL inherit the same inaccuracies.
If cruising coastal Tasmania or anywhere in Australia/Europe/Americas etc give the sharp hard object shown on the charts a wide berth of 2 NMs to be sure.
I have found my Garmin chart plotter with most up to date charts failing to show a small reef 1.1 Mtr below the surface off Menorca, Balearics. Spain.
My parallel plotter program on the Laptop below, using the latest CMAP charts showed the small reef. I was 500 Mtr offshore and saw the potential reef as I passed. The water color showed the obvious.
I should have been 2NM off shore!!!
The rules are check, check, check and eyeball and never go close to shore for the first time unless the sun is high and visibility is clear. Reefs do tend to grow over a couple of hundred years and Captain Cook may have been on the Rum the night before he charts a reef.......
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Old 05-01-2015, 16:55   #43
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Re: Another foundering how do chart plotters get it wrong

Melbourne to Hobart yacht Seduction runs aground on return voyage, crew rescued off northern Tasmania - ABC News (Australian Broadcasting Corporation)
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Old 05-01-2015, 17:42   #44
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Re: Another foundering how do chart plotters get it wrong

Another factor to consider is that many vector chart programs such as CMap hide detail at small scales. Have to be very careful about this and zoom right in to see what is actually there. It would be quite easy to plot a course through a small island set a course and not keep a good look out especially if crossing an ocean. I have almost done this and suspect this is the reason for other groundings.

Andrew
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Old 05-01-2015, 17:51   #45
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Re: Another foundering how do chart plotters get it wrong

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Originally Posted by lordgeoff View Post
THE TWO MOST DANGEROUS ITEMS TO BRING ONBOARD ARE ARRIVAL SCHEDULES....
AND PAPER CHARTS.
FACTS
1 GPS position is always accurate at sea to within a few meters.
2 Chart plotter electronic maps are accurate copies of paper charts.
3 Paper Charts are inherently inaccurate. Sextents are wonderful things and Captain Cook was an amazing navigator. On a good day however he could be inaccurate by 1 NM or more. Therefore electronic charts WILL inherit the same inaccuracies.
If cruising coastal Tasmania or anywhere in Australia/Europe/Americas etc give the sharp hard object shown on the charts a wide berth of 2 NMs to be sure.
I have found my Garmin chart plotter with most up to date charts failing to show a small reef 1.1 Mtr below the surface off Menorca, Balearics. Spain.
My parallel plotter program on the Laptop below, using the latest CMAP charts showed the small reef. I was 500 Mtr offshore and saw the potential reef as I passed. The water color showed the obvious.
I should have been 2NM off shore!!!
The rules are check, check, check and eyeball and never go close to shore for the first time unless the sun is high and visibility is clear. Reefs do tend to grow over a couple of hundred years and Captain Cook may have been on the Rum the night before he charts a reef.......
I'm sorry but the emphasised section of your post makes no logical sense a all.

If your claims are correct, then the electronic charts are also inherently inaccurate being that they are accurate copies of the (inherently inaccurate) paper chart.

I have no beef with the other parts of your post, they are (IMO) quite sensible and I concur with them .
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