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Old 15-05-2008, 17:32   #1
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Dangers in Electronic Charting

This article by Nigel Calder is very good at explaining the inherent and hidden dangers of relying only on electronic charts.
A bit long winded but worth studying
http://www.pcmaritime.co.uk/leisure/shopping/pages/charting/calderelectronicchart.pdf
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Old 15-05-2008, 17:47   #2
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Pfft! Nigel Calder... who needs him?

I can tell you all about what happens when you lose your electronic charts. I had my navigation laptop fly across the salon and down into a hull a few days back.

There I was, on a bouncy day without navigation. I had assumed the worst and have never seen a computer survive such an impact, but I was very thankful to see it fire up and work well enough to get me back to a safe anchorage.

BUT... if it wasn't for that computer surviving, I would have been without any other navigation except my GPS, which had a breadcrumb trail to follow back, but was not desirable.

I had always thought of electronic charting as a convenience. Using them for so long without incident caused me to be careless and rely on them 100% for the delivery I'm on.

The only time you can use electronic charts for 100% of your navigation is if you have a fully redundant backup (as in a 2nd laptop ready to turn on and work just like the first). I didn't have that backup and I nearly paid the price of having to turn back and follow my breadcrumbs to my previous night's anchorage.

People often make the statement that electronic navigation will fail you because it requires electricity to work. Then again, most modern yachts (unfortunately) can't be run without electricity for any length of time anyway:

*Refrigerators storing food
*Starter motors
*Electric windlasses
*Lights to read your paper chart by
*12VDC Solenoid to open your propane connection to eat
*Depth sounder
*Knot log and wind
*Compass light
etc...etc...

In any case, the argument for not relying on electronic charts due to their need for power to be used it a pretty weak one... since most cruising yachts can't be safely navigated without electricity anyway.

Having backups on the other hand... crucial. That goes for a Garmin, laptop and even probably for paper (what happens if you get them moldy or wet somehow and can't read them?)


(my 2 cents... free and worth nothing)
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Old 15-05-2008, 18:46   #3
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Quote:
This article by Nigel Calder is very good at explaining the inherent and hidden dangers of relying only on electronic charts.
The same could be said of light bulbs too. There are inherent dangers in everything. You can manage the risks or you can die by them. Nothing works that good as to be fool proof. Fools always manage to exceed expectations.
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Old 15-05-2008, 19:19   #4
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I keep one of the "waterproof" chartbooks to look at in the cockpit and usually have the Garmin plotter running. We have several handheld GPS units we could call backups.

On trips, it is good to have paper charts to record your position as you go along. Then you have a record of the trip and if the electronics go out well you should be able to navigate with a compass and hourly or faster GPS fix checks.

If anyone can't navigate using basic charts and fixes, time and speed checks, basic navigation skills marking a chart with compass headings and course lines, following them I suggest LEARNING how to do it. Do not rely on electronic navigation on its own. Have a backup plan/equipment and be able to use it.
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Old 16-05-2008, 02:46   #5
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A few cautions:
Don’t drop your electronic nav’ gear down the companionway.
Don’t drop your sextant down the companionway.
Don’t get your electronic nav’ gear water soaked.
Don’t get your paper charts water soaked.

Hmmmm; I think I see a pattern emerging ...

BTW: The advent of GPS, and my inherent laziness, diminished my (once expert) piloting skills.
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Old 16-05-2008, 03:49   #6
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Perhaps some of you missed his key points about inherent errors from presentation……. where paper charts are normally about 1000 dpi and electronic at about 100 dpi and also scaling issues that can mislead a new navigator unless he is aware of it.

I just thought it was a good reminder for anyone relying solely or having experience only with electronic charts

Excerpt:
“The relationship between a paper chart and its electronic display is often 1:6.25. That means 1:20,000 paper chart is now displayed at a scale of 1:3,200.

Let’s consider an area of an original survey that was done at 1:10,000, with a positional accuracy within +/–15 meters. This area was found to be foul with rocks. The chartmaker, working at a scale of 1:20,000, showed a couple of these as close together as possible using traditional drafting techniques, which is to say about 2 mm apart (representing 40 meters in the real world).

No sane navigator plotting on this paper chart would try to take a vessel between these displayed rocks. But now this chart gets digitized and displayed at 1:3,200.

The space between the rock symbols on the display has just increased to 2 x 6.25, or 12.5 mm.

All of a sudden, it looks like I can take my boat between these rocks, especially when its position, based on my WAAS-corrected GPS, is displayed with pinpoint accuracy.

Unfortunately for me, there is no gap between these rocks — just another rock the chartmaker could not show at the original chartmaking scale of 1:20,000.

Overzooming a chart — i.e., using it at a scale for which it was not designed — is one of the cardinal sins of navigation. All electronic charts are overzoomed to some extent, with those found in the recreational marketplace typically grossly overzoomed.
T
o compensate for this, in theory, any navigator using electronic plotting should place an imaginary
circle of possible error around the boat’s plotted position.

This circle should have a radius equal to the allowable error that was used in plotting the features on the chart.

Note that this circle of error does not represent errors in plotting the position of the boat, which will be phenomenally accurate, but instead represents the extent to which the features around the boat may be out of place on the chart.

All potential hazards should be kept outside the circumference of this circle, or, put another way, if any comes inside this circle, we are clearly into the realm of eyeball navigation.”
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Old 16-05-2008, 04:58   #7
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Perlagic's quote illustrates that it is kinda dumb to think that digital charting is super accurate. When navigation near hazards it is ALWAYS best to use traditional eyeball navigation. Even paper charts can be off, especially in out of the way places.

And one should ALWAYS have paper charts of the region you are navigating in and know how to plot manually.

We DO rely on electricity, but we can navigate without out it, drop and anchor, and make way if there's wind.

Relying on e charts is foolish and imprudent.
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Old 16-05-2008, 05:09   #8
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I have to agree with Pelagic and defjef.
Sure 'Waratah' will have all the nice electronic instruments and equipment, chartplotter included. It makes life a lot easier, and hey, this is 2008.

But I will never, and have never, sailed anywhere without paper charts.

Last year I was invited on board of the Anzac class frigate HMNZS 'Te Kaha', which was on a visit in Shanghai. I was surprised to see that there were no more paper charts on board. Surely a lot has changed since I started sailing.
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Old 16-05-2008, 05:16   #9
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There were several things in the Calder article which I think he overstated. Keep in mind when considering the following that I am usually referring to official raster charts ie raster copies of the official original paper chart, but S-57 charts follow similarly when applicable.

Regarding the scaling of the chart the electronic charting system (ECS) I use allows viewing the chart at "Compilation Scale" which looks to me to be the same as the same paper chart (although I have never bothered to hold a a paper chart beside it to check for sure). Despite what I took to be the inference in the article that the charts pixilate at this, the charts are perfectly sharp when so displayed (in fact it is the default display).

Regarding the DPI matter - the ECS I use does not allow zooming to the extent that the image pixelates, nor allow zooming to an inappropriate amount for navigation - it either automatically takes one to a bigger scale chart or if such is not available it hides the chart (a click to zoom out again restores it instantly).

Regarding his comments regarding mix and matching bits of different charts to make up an electronic one (resulting in scale errors and dislocation of features) I do not believe this happens with official charts, especially with raster ones which are an exact representation of the original paper one and so just as accurate (or inaccurate, as the case may be ).

Again, his reference to not being able to produce error circles is not a general fault. It is common in ECS's to be able to draw a danger highlight around dangers to whatever size wanted (but generally as a polygon rather than a circle) - furthermore, the ECS I use will issue a voice warning "Danger Ahead" and display a flashing annunciated alarm should the vessel's look ahead vector stray into that highlighted zone (whether the chart is raster or S-57), something a paper chart with error circle will never do .

Perhaps his comments are more appropriate to simple plotters and charts from non official sources but certainly should not be taken as being general.

His comments warning about relying on charts and electronic navigation aids as being exact is well taken but I got the feeling with his submarine and cruise ships hitting things, etc examples he missed the point that despite one being able to point to such events, electronic navigation aids have actually increased safety greatly.

A common misunderstanding I often come across (but not in the article) is that navigation using electronic charts is dependant on the GPS being operational, whereas in fact the ECS's I am familiar with allow conventional navigation on them using easy tools for drawing bearing lines, dividers, marking positions, etc all much more easily than doing so on a paper chart (analogous to using CAD rather than a drawing board and paper). Obviously small plotters are not so capable.

I thought the article very good but gave me the impression that all charts and software/hardware had the problems he outlined. Perhaps he could have pointed out that equipment and charts exist that do not show the faults in electronic form that he outlines.
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Old 16-05-2008, 05:42   #10
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All your points are well made Midland, however I thought Calder’s article was geared as a useful warning more towards the neophyte who believes his charting system which places him in the right dock place at the marina, will have that same accuracy everywhere else.

Also he did distinguish between commercial and recreational plotters
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Old 16-05-2008, 06:40   #11
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...I thought Calder’s article was geared as a useful warning more towards the neophyte who believes his charting system which places him in the right dock place at the marina, will have that same accuracy everywhere else...
I agree and reinforce that too Pelagic.

It may be worth mentioning that neophytes should also be aware that if they navigate on paper they should not assume that charting errors go away (can't remember if Calder pointed that out or not - and I'm not downloading the article again to see 'cos I'm on slow GPRS at the moment ).
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Old 16-05-2008, 07:31   #12
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We DO rely on electricity, but we can navigate without out it, drop and anchor, and make way if there's wind.

Can you really? I almost never disagree with DefJef, but in this occasion I have to.

Do you have a leadline?

Do you have something to throw overboard and count off the seconds as it passes from bow to stern to estimate your speed through the water?

If so, can you do this single-handed while leaving the helm because autopilots don't work without electricity?

If you can't do the above, you can't plot your positions and use dead reckoning, therefore, I submit that you can't navigate without electricity on your boat.

You could take a fix here or there with a hand-bearing compass, but what if you have nothing to take a fix on due to visibility, rain, or night (where you couldn't see your chart in the first place without electricity)?

So... by extension, saying electronic charts aren't reliable due to electrical issues isn't a good argument - since the average cruising boat can't be navigated without electricity in this day and age anyway.

Aside from pointing out my own stupidity relying on a single laptop for navigation (with only a backup GPS to get me back to where I started that day), this was the point of my post - to refute the argument that electronic charts are in any way less safe due to their use of electricity.
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Old 16-05-2008, 08:03   #13
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Last year I was invited on board of the Anzac class frigate HMNZS 'Te Kaha', which was on a visit in Shanghai. I was surprised to see that there were no more paper charts on board. Surely a lot has changed since I started sailing.
This has been well written about, the modern navy no longer sails with paper.

We carry paper but.........it sure is nice to have modern stuff. The lights on the Detroit river can be a bit confusing and it's nice to have radar when freighters are around and vision is not the best.

We are pretty lucky to be able to rely on the combo of paper, modern electronics, the Mark 1 Eyeball, and experience.
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Old 16-05-2008, 08:20   #14
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It all comes down to having a combination of tools at our disposal for navigating and understanding their strengths and weaknesses. This is what will help keep us out of trouble.
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Old 16-05-2008, 08:39   #15
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It all comes down to having a combination of tools at our disposal for navigating and understanding their strengths and weaknesses. This is what will help keep us out of trouble.
A perfect post.

Well put. The essential rule is to rely on 3 or more inputs to your navigation. I feel very nervous when I have less than 3, or when one doesn't agree with the other for some reason.
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