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

[HeartsContent]

Having read several threads about the need to have paper charts as if these are much more accurate than electronic, it got me thinking. In reality, it would seem to be the opposite wouldn't it? Electronic charts can easily have all the latest updates making them far more accurate than paper - if you update them.

Where I think the confusion comes in is coupling GPS with Electronic charts. This does not always go well and more and more mishaps seem to be highlighting this.

I have sailed right down the middle of an island before on my GPS and had land where the GPS said was a channel. The fact is that not all charts are all that accurate and GPS does seem to "get lost" sometimes - often by huge margins.

The issue isn't' electronic charts, it's that we are relying on a single method for position. This will lead to the same problem, electronic or paper if the GPS position is wrong.

A couple of bearing hacks will resolve most issues - assuming you can taking visual bearings.

Thoughts?

[jackdale]

Agreed

If you are using charts that are off some miles, a visual fix will work well. If you use a GPS and transfer a lat / long you are hooped.

[goboatingnow]

I think its important to separate position fixing and charting. Not physically separate , but mentally. Position fixing today is almost exclusively GPS based and a prudent navigator backs this up with mark I eyeballs and or other visual fixes where appropriate ( or radar verification where fitted)

Electronic charting is a great advantage. Primarily because the cost and space need to build a comphrensive paper chart set for an extended cruise is very large. Not to mention in many countries its actually very difficult to get charts. Paper is in most cases relegated to the role of backup and planning and is to be recommended for that.

Accuracy is a length of string. No more then your digital watch may be very precise, it isn't necessary any more accurate, hence we have to bear in mind that positions fixed on a chart , whether electronically derived and plotted or manually or via a combination always have an inherent inaccuracy and that must always remain in the navigators mind.

Dave

[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.

[LJH]

I agree with Dockhead above. In fact I usually get the paper charts first and pick up C-Map chips later in the planning phase when I am going to a new area. The cost adds up. I need about 35 Imray charts for next summer!

It is much easier to plot your position relative to a land mass on a paper chart than it is on an electronic chart when the chart does not reflect reality. I always have paper readily available in coastal areas.

[nigel1]

Just finished reading an interesting publication on the use of ENC's (NP231 Admiralty Guide to the practical use of ENCs)
Good explanation on the dangers of over scaling of ENC's.

Section 4.3
Zooming in to a larger scale
When compiling a chart, the accuracy of the position that is seen on the chart will depend on a number of factors, and which includes the accuracy with which:
The position of the real world object was determined originally.

This position is then plotted on the survey by the cartographer.

The survey position is then translated into the horizontal datum used to draw the final chart where this is a different to the survey datum (WGS84 for ENC's, as used with GNSS).

The position is then plotted on the chart by the cartographer

It is likely that a small error will be introduced at each stage, and in the worst case scenario, these individual errors will add up to one large error rather than cancel each other out. The aspects listed above related to plotting positions are scale dependent.

If we assume a cartographer can reproduce a plotted position to within 0.5mm on the chart, then this may be a total of 1mm when one considers the possible error error introduced when plotting the survey, and then plotting the chart from the survey. If the cartographer is plotting to a scale of 1:1000, a 1mm error will equate to to only 1 meter in reality. However, if the cartographer is plotting at 1;700,000, a 1mm error will equate to 700 meters in reality. The same 700 meter error will become an error of 70cm if plotted on the 1:1000 chart.

It is for this reason that ENC producers will not normally produce a chart on a scale larger than the original survey, and it is recommended that ENC's are not used for navigation if zoomed in to more than twice the original scale.

Bet the captain of the Costa Concordia wished he had read this book.

[noelex 77]

Originally Posted by HeartsContent

The fact is that not all charts are all that accurate and GPS does seem to "get lost" sometimes - often by huge margins.

Charting errors are very common, but if the GPS is "getting lost" something is wrong.
My GPS has been is on virtually 24/7 without a single episode of getting lost over the last 5 years.
Boat owners do show far more tolerance for these glitches, often blaming the GPS system when invariably something wrong the GPS unit itself, or its interfacing. There are rare cases of jamming ( although I have never personally seen one) but these are localised

Originally Posted by HeartsContent

This will lead to the same problem, electronic or paper if the GPS position is wrong.

A couple of bearing hacks will resolve most issues - assuming you can taking visual bearings.

Thoughts?

It's not the GPS that is wrong, it almost always the chart.
However i agree completely about the need to check by other means. its important to realise that "traditional" navigational techniques like taking a three bearing fix, or a clearance bearing, largely take these charting errors in to account and will result in a reasonably correct relationship between the vessel and dangers. (Radar will as well)
Its vital to employ these tradition techniques when the margin for error is small.
These techniques can still be done on electronic maps.

[carstenb]

I agree completely with dockhead here. Another positive is that it is possible to have two paper charts in front of you so if working on a detail chart your eyes can flip over to the bigger chart easily.

Since most of us here are grey haired, it is also easier to paper when you wear reading glasses. Not to mention that if you plotter does not have a repeater below deck, then it can get very cold and wet sitting in a cockpit planning your route

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.

[sailorF54]

AFAIC
A typical Mega Wide C-Map chip will contain more than 4000 charts for about 400 $ (price for Europe, that includes royalties for the relevant Hydro Services): 10 charts for a buck.
example: 4469 charts in MW3 EW-M010 WEST EUROPEAN COASTS AND WEST MED.
for $358 at some well-known outlet in Florida...: 8 cents per chart
I have to live with it for long-range sailing...

[GordMay]

Originally Posted by Dockhead

There are a few benefits of paper charts:
... 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 ...

Indeed.

[goboatingnow]

Originally Posted by LJH

It is much easier to plot your position relative to a land mass on a paper chart than it is on an electronic chart when the chart does not reflect reality. I always have paper readily available in coastal areas.

I don't understand this, you can plot on paper and I can input a waypoint faster. I plot on paper too but I don't see what you mean specifically here.

Dave

[nigel1]

Originally Posted by goboatingnow

I don't understand this, you can plot on paper and I can input a waypoint faster. I plot on paper too but I don't see what you mean specifically here.

Dave

I think this is referring to a position plotted on a paper chart using bearings and or ranges, establishes a position relative to the land mass or other object, rather than to a chart co-ordinate, and that its quicker to do this on a paper chart than on an electronic one.
Although, with some practice, it is just as quick to perform the same function on an ENC, I'll go as far to say, even quicker if you make your self familiar with the equipment

[FruiVita]

In today's electronic world many people navigate by iPhone or iPad with GPS as a backup but with paper charts in the nav desk in case power is lost. I sail in the Chesapeake which is notorious for shallow depths so I always take a few minutes to verify my iPhone app with my paper chart. Better safe than grounded.

[nigel1]

Example of combining traditional nav methods with an electronic chart.
Shows 3 bearing lines plotted

[Greggegner]

I carry paper charts and hope to continue to. When coming into a new harbor I use the chart plotter zoomed in where I can see lots of detail and keep the paper folded to see the overall the lay of the land. Unless the harbor is very large I don't like charging the zoom level.

For planning paper is ok, but we use the PC and Nuno software. We can quickly build routes, get distances while changing scale as needed. It is fairly cheap, simple and has Active Captain built in. Many times choosing marinas and harbors deal with features and reviews. Having phone numbers and marina names up to date is also very helpful.