Paper vs. Electronic Charts - what's really the difference?

[Dockhead]

Originally Posted by cal40john

At least for my Garmin Bluecharts I do have some information disappear at larger scale (smaller area, zoomed in). I haven't figured out rhyme or reason and I have played with the detail level menu as well, that has some interesting effects that don't always make sense to me either.

That's the nature of the beast.

My pet peeve is the Swash Channel leading to the entrance to Poole Harbor as rendered on my RL80 plotter with CMap NT+ cartography (which I have just retired). For some reason, the damned channel markers don't show up unless you are zoomed in so far you can hardly see to the next buoy. It was a real PITA in bad visibility until I simply memorized the position of all of the buoys. That can be positively dangerous in unfamiliar waters -- the loss of detail even at moderate scales.

As far as I know, raster charts don't suffer from this.

But I will always prefer to study and prepare using paper charts.

Another thing, which I don't think anyone mentioned -- what a joy it is to hold and use paper charts! They are things of beauty. If even only for aesthetic purposes, I would never want to give up the joy of a full sized Admiralty chart, folded once, laid out on my chart table, gently illuminated by my chart lamp. Bliss! No electronic gadget, no matter how cool (and I love my new Zeus plotter!), can substitute for this aesthetic joy.

[noelex 77]

Originally Posted by Dockhead

Right -- I bet some people are not aware that automobile GPS works differently -- your vehicle icon is "snapped" to the nearest road, unless you switch off that function (as you can in some SUV nav systems, like on my Range Rover, for going off road). In short, the system assumes that you must be on a road, so if your position plots out 50 meters to the side, it moves you over to be on a road. It gives a false impression of greater accuracy than it has.

True but terrestrial GPS units have a much harder time. Their view of the satellites is often obscured. Buildings are great at creating multi path distortion. Most aftermarket units just have an antennae on the windscreen with a big metal roof behind them.

It's a wonder that they manage as well as they do

[carstenb]

Originally Posted by Dockhead

Another thing, which I don't think anyone mentioned -- what a joy it is to hold and use paper charts! They are things of beauty. If even only for aesthetic purposes, I would never want to give up the joy of a full sized Admiralty chart, folded once, laid out on my chart table, gently illuminated by my chart lamp. Bliss! No electronic gadget, no matter how cool (and I love my new Zeus plotter!), can substitute for this aesthetic joy.

Dockhead,


They are pure artwork. I can spend a lot of time just enjoying looking at a good paper chart.

[Thonord]

Originally Posted by Dockhead

But my plotters have all shown a circle of uncertainly of the fix. Very useful at the larger scales.

Yes, prolly one of the DOPs. Useful, but potentialy treacherous.

Dilution of position (DOP). Its should be noted that they, Horisontal-, Vertical- Geometric-(from LoranC) and PDOP . Don't remember what P stands for, but its 3D are results of digital wizardry.

GDOP is easiest . Its pure averaging and disguises large errors of short duration.

Tom

[goboatingnow]

Garmin plotters actually dont plot a DOP ( Dilution of Precision) circle, Garmin uses a EPE (estimated Position error) which according to them is a conbination of DOP and other factors such as signal strength etc Since Garmin dont actually reveal exactly hows its computed its somewhat useless. It is in effect a probability circle, some experts have indicated they believe its a 90% circle, but who knows.

dave

[noelex 77]

I find an indication of the GPS accuracy is an important parameter. It's always worth having this visible on the screen (as a circle) or at least a numerical number. An indication if its a DGPS, or only GPS fix is also useful.
The only caveat I would add is that can a false sense of security with maps that have much bigger errors in their cartography.

Where it is as most use is where you are comparing your position to known position point from the GPS, like an anchor alarm.

In many ways the definition of the error is not important once you know the characteristics of a particular GPS unit.
For example for my Garmin HH a normal fix outside is indicated with an error of as "2-3m" ( I have no idea if this is 95%, or something else, but I know its a good fix). If I bring it down below a typical fix has an error of 5-10m. If I shut my metalised blinds it occasionally can jump up to 15-20m. In these cases I am far less confident in the fix and therefore less worried that a position error indicates I might be dragging anchor, but I can still check the main GPS with an external antennae and therefore a constant good fix.

[goboatingnow]

yes but just be aware that the EPE in Garmin is only an "indication" of accuracy. Quantative evaluation is actually difficult. In other words, just because theres a circle doesn't mean that you are inside it.

dave

[HeartsContent]

My take is that GPS is very accurate, as long as you are receiving a good signal. What happens then is where I think problems come in as the device starts a form of DR.

The value of paper charts reduces significantly as you get closer to things. The ability to constantly do bearing checks is great when you have a navigator onboard.

My perspective is that the electronic chart plotter does this constant position check that a dedicated navigator (better quartermaster) would do. All you have to do is "check its work" occasionally to ensure it is correct. That's how I navigate.

Radar is another excellent method of establishing a position fix and finding markers. The overlay function will quickly validate errors.

Locally, I know where it's right and where it's wrong. If the barrier islands and sand bars would just quit moving, we'd be just fine!

[Thonord]

Originally Posted by goboatingnow

Garmin uses a EPE (estimated Position error) which according to them is a conbination of DOP and other factors such as signal strength etc Since Garmin dont actually reveal exactly hows its computed its somewhat useless.
dave

I believe Garmins EPE is similar to Circular Error Probable (CEP) i.e. a 50% probability.

It is my philosophy to err on the side of caution. I may have wasted a lot of time during my life, but I'm still here to be embarrassed about it.

Tom

[Thonord]

Originally Posted by HeartsContent

My take is that GPS is very accurate, as long as you are receiving a good signal. What happens then is where I think problems come in as the device starts a form of DR.

I didn't know that GPSs has a DR capability. I know the old Transit system had. It had to! Based upon external sensors.

Chart plotters may have DP, but a chart plotter is not a GPS even if it has a GPS built in. GPS is only a sensor. It provides a geo-position, True heading , Speed over ground (SOG) and "exact" time. Geo-position has an element of graceful degradation, from 3D to 2D, but when 2D fails - all that is left is Time.

Originally Posted by HeartsContent

My perspective is that the electronic chart plotter does this constant position check that a dedicated navigator (better quartermaster) would do. All you have to do is "check its work" occasionally to ensure it is correct. That's how I navigate.

Radar is another excellent method of establishing a position fix and finding markers. The overlay function will quickly validate errors.

Seconded

Digitalization is here to stay, and rightly so! But I am old enough to remember the introduction of "Digital" Radar.

Statements, back then, like: "My radar is so sensitive that a seagull gives the same size echo as a small boat" never seize to amuse me.

But, back to topic. Charts.
Digital charts should be the standard and are the way of the future, but I will always prefer paper.

Coffee stains on a chart may bring back fond memories. Spilling coffee into a keyboard is just darn expensive!

Tom

[noelex 77]

One constant theme throughout these sort of threads is pleasure in using paper charts.

With this I agree wholeheartedly agree. They are are a pleasure to use. Almost sensual ( OK now I am getting carried away )

There is also a mental challenge. I love in solving mathematical puzzles.

These goals are fine, sailing is about pleasure, not rules, but when the SHTF an instant accurate position fix is what is needed.

Beginners are often convinced that a paper chart with a HB compass and perhaps a sextant is preferred way to navigate.

In truth, it's like a vintage sports car, great fun, but not the ideal way to travel to work each day.

Make sure you have the skills. The recent thread about tidal streams shows how poor knowledge of traditional navigation can create problems.

I wear an mechanical watch, why, it gives me pleasure, is it as accurate, or as functional a quartz watch. No.
If there is an EMP, or there are no batteries available, my watch will keep working. Is that why I wear it. No.
Generally, a digital electronic quartz watch is the most practical option, but knowing how to tell the analogue time is still a basic requirement.

[Andrew Troup]

n77 identifies an important common thread - at least, it's clearly important to some... which reminds me in some ways of differences between books and ebooks.

One thing about books that some people enjoy is the ability to add value by scribbling insights, corrections, marginal notes, underlining or highlighting, slipping clippings (or even flat physical objects) between pages ...

There are ways of simulating at least some of these acts electronically, but we climb on a treadmill if we want to carry these snippets of added value forward throughout our lifetimes. Backups, transferring to new media, platforms or paradigms, yadda yadda... They also effortlessly and incidentally act as a record of places we've been, and hint at what we found to explore when we got there.

When it comes to charts vs eCharts:

I've still got the charts which capture the discoveries of my youth. Yes, they've captured salt stains and food and drink, but they also show surprising and hard-won information about uncharted dangers, misleading appearances, extraordinary eddies, useful transits, sketches of headlands, unexpected shelter ...

I may never need any of this information again, so even if I could easily transpose it every time someone came up with a new improved format or platform, I doubt that it would be worth the effort.

Whereas keeping the charts is no effort whatsoever, and they have captured something intangible, something which I value.

[sneuman]

Originally Posted by Dockhead

There are a few benefits of paper charts:

1. They work without electricity, and don't depend on the functioning of any electronic device.

2. They have a single scale -- your eyeball does the scaling. So they are much better for planning -- you can see the whole passage at a glance, yet all the detail is there. Details -- including dangerous obstacles -- disappear at larger scales in electronic charts. Planning with electronic charts is tedious, zooming in and out along the whole route. I bet plenty of groundings and other accidents have occurred as a result of mariners' failure to do this properly.

3. You can do chart work on them.

So as much as I love electronic gadgets, I personally am uncomfortable sailing anywhere for which I don't have paper charts. Like Dave said, paper charts are very expensive, and I'm sure the day will come when I'm covering too much ground to buy paper for every nook and cranny, forcing me to rely on electronic charts only. I'm not looking forward to it.

+1. My thoughts precisely.

[carstenb]

Well yes andrew, and I heartily agree with you but it is only old farts like us that appreciate these things.

I love the feel of a book in my hands. It has a physical presence. An Ibook does not. An Ipad does not feel the same.

The same is true for photos. Yes showing photo on you Ipad is easy, but not the same as holding the photo in your hand(nor can you write on the back of the digital one that this is your old aunt mathida)

[banyandah]

The difference is they are different tools that do the same thing plus they're own specialty. Paper charts are great for planning and to have for backup. As mentioned, digital are cumbersome for perusing, which can lead to mistakes, whereas, once on the way, with your vessel a blinking icon on them, they're a handy nav device.

We carry both.