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Old 19-05-2008, 06:40   #46
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Originally Posted by Pelagic View Post
Thanks Sean, I was wondering where you were going with all of that, but since you have been stuck up the creek without a paddle, I'm happy to make allowances LOL
Thank you for the allowance.

You probably know how the mind gets during a delivery. Feeble. ha ha
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Old 20-05-2008, 06:09   #47
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With Nobeltec I get the Passport Deluxe charts. It comes with the vector, raster (BSB) and photo charts all in a set. The vector charts all line up and I can't tell when it moves from one chart to another except by looking at the title bar. With the rasters, however, I'd say over 10% of them are off at the seams. This ranges from just a few feet to 50 and sometimes 100 feet. Since they come from the same datasets, I'd say this is a case of the vector charts masking the errors and creating a false sense of accuracy. And I see this in the Passport charts as well as Maptech charts, including in some river charts.

But I find that the markers on the vector charts are almost always dead on. In fact, I plot a course off to the side of the marker to avoid accidentally running into them at night.

Since I only have done near shore and Intracoastal, I bet the accuracy of the actual data is better than many areas. I haven't found a time when the inaccuracies have caused an issue. Even though I have always had a healthy reserve in trusting ANY one method, reading this article and this thread is a good booster for my skepticism.

With the photo charts, there are 3-4 on the Alabama coast that are spun about 20 degrees. Obviously a simple encoding problem. A corrupted object could cause this, but 3 in a row sounds more like a programming error or typo. And bad quality control. These were from Maptech about 6-7 years ago. The photo charts normally, however, all line up at the seams. I'd attribute this to the fact that they are produced by later technology. This doesn't mean they are necessarily dead on at all points within the image, but I don't think they can be off by more than a few feet. Still, I agree that no chart should just be blindly trusted.

Coming into Ft. Meyers after dark it was wonderful to zoom in and place the boat between markers sometimes only 30 feet apart. But, I didn't drive by the chart, I used the chart to tell me where to aim the light to pick out the markers. Only trust your eyes, and double check them.

Edit: As a side note, my street map GPS in offroad mode sometimes shows the roads off, in one case, over 150 feet. In "follow streets" mode, the vehicle always follows the road. So it's not showing actual position, but the position on the map where it thinks I am. Sometimes in street mode it shows me on a parallel street. So you have to be careful with them as well.

-dan
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Old 20-05-2008, 07:33   #48
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I'd say this is a case of the vector charts masking the errors and creating a false sense of accuracy.
The data is the same source and it is inaccurate. You can never know which is the most accurate because neither are accurate. Uniform accuracy is not assumed with any data such as navigation charts. The critical part is you never know for sure which data is less accurate or more importantly where. It's not a quality control issue. It is a lack of data issue.

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But I find that the markers on the vector charts are almost always dead on.
NOAA locates them by GPS so they will be most accurate. When the USCG tender plants them they note the exact location. The rest of the data is not as accurate. This is a case where the buoys are right but the rest of the map is not. They don't make maps that way - they never have. The actual map data is stored as vector but multiple sources of data are merged to make a final chart. All the data is not to the same degree of accuracy because it could never be collected at the same time or using the same methods. Land outlines, bathymetric data are all from vastly different sources and does not register to the same point every place. When both are wrong there are statistical processes that can mitigate the error but the error can never be fixed because there is no information to fix it from.

Consider the primary purpose of these charts are not for recreational boaters. It's about making trade dollars and commercial shipping. You'll find primary navigation routes used by commercial ships to be highly accurate. You'll find water too shallow for a commercial ship has no serious priority for details and accuracy to the same degree. Bathymetric data is perhaps the worst. It comes from old sources and the priority for update is quite slow.

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A corrupted object could cause this, but 3 in a row sounds more like a programming error or typo. And bad quality control. These were from Maptech about 6-7 years ago. The photo charts normally, however, all line up at the seams.
They line up at the seams because there is a function to do that. It pushes all the error from the edges across the whole chart. It actually makes the accuracy worse. Photos have distortion from the camera lens and that error is greatest in the edges. In high accuracy mapping you throw out more than 50% of the image on the negative and use overlap from adjacent photos. They can't do that when they never took the photos low enough to get overlap. They don't take all the photos at the same time. The photos used in these maps are scavenged free from the USDA and packaged for sale. The photos were basically crap to start with. They don't take photos for this specific purpose. Consider photo charts to be of no navigational value at all. The can show information visually without being accurate. You see a building and you can believe it's there just not exactly as indicated. The photo maps were an attempt by the resellers to add value to charts you can get for free. The photos come in handy when you need to know where a road might be or if there is something over a hill when you anchor. Lots of good information but not for navigation. I would not rely on a smoke stack location in a photo so you could pilot a course. I think you have seen how bad it can be and that looking right does not assure being right.

You read a chart to gain information and not all the information is important to you at any one time. The key is to look for the things that are important and then judge the accuracy implications. You still need verification such as what you can see with eyes or radar or collaborate from multiple sources. There is no assurances so looking for more verification needs to be a constant part of your Piloting skills. Things change and information that was once accurate might not be accurate at the moment.
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Old 20-05-2008, 09:57   #49
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I find all this talk about "accuracy" rather silly. 100 feet off? 50 feet? 100 meters? Who cares??? In my home port my chartplotter and a WAAS gps puts my boat on the correct side of the dock, within a very few meters of my actual spot. It's impressive. But...

Except when I am trying to find a specific fishing spot, those kinds of numbers are complely irrelevent to me. They might matter if I navigated by remote control, inside a black box without looking around. When I need that kind of accuracy on close in dangers, I am on deck, with my eyeballs on the real world, NOT on my chartplotter. If I need a fix with that accuracy, I am getting it from my bearing compass and a large scale harbor chart, rendering all datum issues moot.

I would never, ever, navigate within a few hundred meters of danger trusting only my GPS and Chartplotter to keep me on the right side of things.

The idea of someone picking one side or the other of a bouy for the autopilot to steer off a an electronic chart is just plain scary.

Getting to be an old fuddy-duddy,
Bill
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Old 20-05-2008, 12:08   #50
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I'm also getting the feeling some of the people "against" electronic navigation are people who don't use all their senses... as in every possible input to navigation:
I am reminded of the time I first learned about PCs, which were very new at the time...before that only banks, higher education, and the government had computers. Anyway, while learning the ins and outs of the PC, I discovered that there were two types of people learning PCs. One type was interested only in what they could do with the machine's software (graphics, numbers crunching), and the other type was only interested in how the machine worked and how they could tweak it (engineer types). Some of the engineer types thought that if you didn't know how it worked, you shouldn't be allowed to us a PC.

I get this same feeling about people against electronic navigation, in that, if you don't know how to navigate the old way, you shouldn't be allowed to use a boat. Granted, there is a large difference between a PC and a boat, but I think that the mind set is still there.
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Old 20-05-2008, 12:28   #51
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I don't hear anybody here saying they are "against" electronic navigation. And I certainly don't think anyone said anything about being forbidden to use a boat if they can't take a running fix.

I have an electronic nav system on my boat (two of them in fact). And they are very handy. So I have no arguement with using them. I do have an argument with anyone who says that traditional methods are obsolete and no longer useful for a long distance all weather cruising boat. For a daysailed boat in familiar home waters, anything goes. If you are going to cross an ocean, being prepared has a very different meaning. If you think that all-electronic systems are good enough for a voyage like that, I will try and talk some sense into you, but I will certainly not say you shouldn't be "allowed" to go.

The danger of an all electronic system is the "heads down" approach it encourages. The real world is OUT THERE, not on the little screen. Here is the classic example: http://www.ntsb.gov/publictn/1997/mar9701.pdf A whole bridgeful of professional sailors who chose to believe what the electronics said, instead of what their eyes were telling them.

Bill
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Old 20-05-2008, 12:39   #52
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I don't hear anybody here saying they are "against" electronic navigation. And I certainly don't think anyone said anything about being forbidden to use a boat if they can't take a running fix.

I have an electronic nav system on my boat (two of them in fact). And they are very handy. So I have no arguement with using them. I do have an argument with anyone who says that traditional methods are obsolete and no longer useful for a long distance all weather cruising boat. For a daysailed boat in familiar home waters, anything goes. If you are going to cross an ocean, being prepared has a very different meaning. If you think that all-electronic systems are good enough for a voyage like that, I will try and talk some sense into you, but I will certainly not say you shouldn't be "allowed" to go.

The danger of an all electronic system is the "heads down" approach it encourages. The real world is OUT THERE, not on the little screen. Here is the classic example: http://www.ntsb.gov/publictn/1997/mar9701.pdf A whole bridgeful of professional sailors who chose to believe what the electronics said, instead of what their eyes were telling them.

Bill

Bill,
The Conclusion on page 45 says that the ECDIS system went to DR mode because of conflicting navigation position inputs and the watch officer was never made aware of this because an alarm was not made loud enough for him to hear that it was now in DR mode.

Anyways, looking out the window may never have saved his butt. What he probably should have done in good old Monday Morning Quarterback retrospect is to take the fix directly off the GPS repeater display and plot the Lat and Long to paper. How was he to know he could not trust his complex ECDIS system though?

It may be the case that things are getting so complex on the bridges of ships that it may be getting difficult to see the forest through the trees..and that is seeing what is most important and most relevant first in an environment of total information overload.

David
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Old 20-05-2008, 12:45   #53
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But I find that the markers on the vector charts are almost always dead on.


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NOAA locates them by GPS so they will be most accurate. When the USCG tender plants them they note the exact location.
Great post Paul!

But just another reminder to the newbie’s out there….You never use a floating marker as a navigational fix.

Surprisingly often after a severe storm or perhaps a collision with a towed barge, that marker has been dragged out of position and may even now be sitting on the wrong side of the danger.

Never assume that the navigational aid is in the charted position unless it is built upon a rock

GreatKetch and Jiffy I think it would be foolish for anyone not to enjoy the benefits of electronic navigation and I don’t see this discussion to be an either/or kind of debate.

I think it is more to highlight the weaknesses in it for new sailors who have been given the “sales pitch” on their $$$$$$$$ navigational package and think that is all they need (anywhere in the world)
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Old 20-05-2008, 12:53   #54
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I have noticed that as well...having tied to daymarks stuck in the Earth (with the Coasties written permission). They are dead on position wise...and I mean within 3 meters.
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Old 20-05-2008, 17:35   #55
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I don't hear anybody here saying they are "against" electronic navigation. And I certainly don't think anyone said anything about being forbidden to use a boat if they can't take a running fix.
I think you're right about it not being said in this thread, but the mind set is alive and well in other threads on navigation.

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Originally Posted by GreatKetch View Post
I have an electronic nav system on my boat (two of them in fact). And they are very handy. So I have no arguement with using them. I do have an argument with anyone who says that traditional methods are obsolete and no longer useful for a long distance all weather cruising boat. For a daysailed boat in familiar home waters, anything goes. If you are going to cross an ocean, being prepared has a very different meaning. If you think that all-electronic systems are good enough for a voyage like that, I will try and talk some sense into you, but I will certainly not say you shouldn't be "allowed" to go.
I think that the traditional methods still have value, but less than they did 10 years ago, and will be of less value in 10 more years...but will still have a place in the right situation if it were ever to occur.

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Originally Posted by GreatKetch View Post
The danger of an all electronic system is the "heads down" approach it encourages. The real world is OUT THERE, not on the little screen. Here is the classic example: http://www.ntsb.gov/publictn/1997/mar9701.pdf A whole bridgeful of professional sailors who chose to believe what the electronics said, instead of what their eyes were telling them.

Bill
I would tend agree, that people will tend to be looking down instead of out and around, but only a little bit more than people do while cruising by the compass...especially in overcast, foggy, or cloud covered night situations. I don't seem to watch my plotter any more than I do my compass, as I need as much attention if not more looking out and around with my eyes.
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Old 20-05-2008, 18:28   #56
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I would tend agree, that people will tend to be looking down instead of out and around, but only a little bit more than people do while cruising by the compass...especially in overcast, foggy, or cloud covered night situations. I don't seem to watch my plotter any more than I do my compass, as I need as much attention if not more looking out and around with my eyes.
Jiffy, you are absolutely right on that one.

When I was involved in designing Super yachts, I made sure the Helm/Lookout position was placed forward of all the instrument and navigational arrays for that very purpose and if I came on the bridge and found 2 heads cluttered around the sonar or GPS…..there was hell to pay!
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Old 20-05-2008, 19:53   #57
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Paul, thanks for spelling out what I was implying. Well said.

GreatKetch. If someone thinks the charts are accurate and find themselves in 0 visibility fog and try to navigate some of the little channels I have been through, 25 feet could spell disaster. So I agree with your assessment, but think the accuracy warning is a valid one to point out.

I try very hard to avoid putting myself in a position where things get critical, but one day I may make a mistake and be in a bad situation. If/when that time comes, then all this knowledge about the minute differences in accuracy of various types of navigation may well be the difference in life or death. I like to know all I can know, prepare for the worst possible situation, and then work like h*ll to make sure it was all a waste of time.
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Old 21-05-2008, 02:42   #58
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......If someone thinks the charts are accurate and find themselves in 0 visibility fog and try to navigate some of the little channels I have been through, 25 feet could spell disaster. So I agree with your assessment, but think the accuracy warning is a valid one to point out.

The Radar, Paper chart prepared with parallel Indexing and the Sounder are my tools for navigating along in the fog and creeping into an anchorage in zero visibility. On the West Coast of Canada in the summer, we sometimes get those conditions lasting for weeks.

Learning how to choose good radar returns when plotting a coastal journey takes lots of practice and observation in good visibility, so that the skill can be easily learned (if you practice!)

p/s and that is also one of my complaints about some of the electronic charts.... They don't always show the land topography to choose the radar return for indexing
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Old 22-05-2008, 08:07   #59
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For those who want to report a nautical chart discrepancy, ask about downloading electronic charts, or have questions on paper chart coverage, a toll-free Navigation Inquiry Line is now operating at the National Oceanic and Atmospheric Administration (NOAA).
The Office of Coast Survey's line at 1-888-990-NOAA (6622)
is answered by a real person weekdays from 8 am to 4 pm (ET).

A similar online inquiry service is available at Coast Survey's Inquiry

See also, the Coast Survey web site at http://nauticalcharts.noaa.govv/
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Old 22-05-2008, 08:58   #60
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If you draw a line between the bars on Put in Bay (South Bass Island) and Cleveland you'll find a cute little pile of rocks known as Gull Isle Shoal. I know a guy here with a barge that makes a good bit of dough plucking boats of that pile of rocks.

Gotta believe many Friday afternoon conversations go like this: "This is easy honey, see we just put the X on PIB and let the boat run."
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