Traditional or digital navigation - which is safer?

[El Pinguino]

Dirt dwellers have been known to call 'variation' 'declination'. That being as it may this isoporic chart shows the global rates of change.
Quite a few places frequented by sailors ( UK/North Sea/Baltic 'frinstance) have a rate of change of 10' or more per year... a degree every six years.... five degrees every thirty....

[Pizzazz]

I think most readers already got the benefits of digital navigation but just for the record:

Digital charts are so much better and safer because in addition to customizing the look, you can easily plot electronic means of navigation (radar bearing, actual depth, COG, wind, tides, etc.). To do this on a paper chart is next to impossible. While it is true that radar resolution is typically 4-5 degrees, you can measure radar bearings to +/- 1 degrees, just look the leading edge. Most compasses are +/- 5 degrees accurate but they measure the change in direction to +/- 2 degrees. If you invest in a modern compensated compass (eg KVH 1000) the accuracy is +/- 0.5 degrees which is an order of magnitude better than you can do with a hand bearing compass.

Variation on the paper charts has been calculated at the time the chart was printed. Recently, the movement of the magnetic pole has been accelerating and updated plotter software adjusts for this. In any case, the error is very small for most cruisers but the electronic method is simple while the paper method involves multiple steps that are error prone.

For me, the bottom line is that through simplification and automation, electronic navigation has made cruising safer and opened up the hobby to many new people. It is an order of magnitude better than paper/sextant/magnetic compass navigation and nearly everyone will be better spending time understanding electronic navigation better instead of wasting time on arcane navigational skills. Hence commercial shipping has switched to electronic only.

Lastly, many of the potential errors in electronic navigation are self correcting. Even if you misjudge a strong current you will still figure it out when you see the movement of the boat deviating from the planned course. With paper/sextant/compass you start doubting your calculations first, then you start doubting your equipment, then you get tired and start making simple mistakes. It does not need to be that hard. But I do understand that some people feel safer with the hybrid model. More power to them.

SV Pizzazz

[jtsailjt]

Originally Posted by El Pinguino

Dirt dwellers have been known to call 'variation' 'declination'. That being as it may this isoporic chart shows the global rates of change.

Quite a few places frequented by sailors ( UK/North Sea/Baltic 'frinstance) have a rate of change of 10' or more per year... a degree every six years.... five degrees every thirty....

But do you use a GPS chart plotter that’s 30+ years old that doesn’t correct for changes in variation and with digital charts that haven’t been updated in all that time? Very doubtful. Changes in variation are no bigger danger to digital navigators than they are to those who use paper charts, probably less.

Even an only marginally accurate, degraded gps yields a more accurate position than traditional navigators could come up with by shooting heavenly bodies and using DR. We’ve been discussing issues that in worst case might cause our digital position to differ from our actual position by a few hundred feet but traditional navigators would have been thrilled with that sort of accuracy. Some inexperienced digital navigators have gotten into trouble by falling into the trap of depending on their digital position to always be within just a couple of feet of actual position because except for on very rare occasions it is just that amazingly accurate. Certainly that overconfidence can bite you but the only reason it never happened to traditional navigators is that once they left their home port in clear weather they never knew where they were within just a few feet and they knew their accuracy wasn’t that good so didn’t fall into the trap of thinking it was.

Anytime I’m navigating in unfamiliar areas or in restricted visibility I always have at least my chart plotter and my iPad Navionics app that I’m constantly cross checking, with OpenCPN running down below on my laptop to be used as a tie breaker if necessary or to cross reference any time I go below, and I also have my radar operating. I’m also making sure my digital depth sounder generally agrees with depths on the digital charts I’m referencing. Just like traditional navigators I’m also looking around for any visual clues. Unless all these sources of info agree to a very tight tolerance, I stop and figure out why. I think my methods are pretty typical of most digital navigators.

Overall, modern chartplotters offer dependable, accurate navigation that’s very easy for even the novice navigator to use, freeing him up to attend to other boating tasks,or to just relax and enjoy himself more. The easy availability of digital navigation has increased safety as well as allowed many more to dare to venture out onto the ocean compared to back when paper charts and DR were our only option. Of course a little common sense and a little healthy skepticism must also be used, no matter what sort of navigation you prefer.

[Benz]

^^But once again, this last guy and Pizzazz won't address the obvious fact that where charts are not aligned with the geoid, which Ping posted a picture of, no amount of cross-checking plotters and ipads and radars will keep you off the rocks. Perhaps they have the good fortune or foresight to sail only where the charts are well-aligned, but I cruise in more places where they are not than where they are.

[Paul L]

Originally Posted by Benz

^^But once again, this last guy and Pizzazz won't address the obvious fact that where charts are not aligned with the geoid, which Ping posted a picture of, no amount of cross-checking plotters and ipads and radars will keep you off the rocks. Perhaps they have the good fortune or foresight to sail only where the charts are well-aligned, but I cruise in more places where they are not than where they are.

Actually this is the condition where having a Radar overlay on the chart display on an MFD does tell you if the chart is aligned to reality or not. When we arrive in a new area I always do a quick radar overlay display to verify that the chart datum is valid.


Also, variation does not come into play when setting the autopilot. You set a course on the plotter. Turn the boat to follow the course and press Auto. This is all done in True coordinates and uses tbe AP compass as a relative measure. If you want the AP to display the course in magnetic then it will apply the variation. Whether the variation is correct or not, there is no change in your COG.

[belizesailor]

To paraphrase Bowditch: A prudent navigator uses all means at his disposal to navigate.

Its not an either or choice, the best practice is to use both...or to at least be prepared to use both.

In unfamiliar waters and/or longish runs I at least keep a physical navigation log and maybe plot position periodically on a paper chart too. This way I at least know where I was should the electronics fail.

Traditional navigation skills are not only useful, but to me at least its very gratifying to do a running fix, celestial fix, etc and have it match (or at least near match) the GPS fix. Its also another means of confirming whether or not the electronic chart is accurate. Too many assume that just because its displayed on a screen that it must be accurate. So much so that I have literally watched bare-ly-boat-ers charters run aground on clearly visible shoals because they trusted the plotter screen over reality (or were so glued to the screen that they never looked ahead!)

[Oceansailor]

I’m convinced that we would see more accidents if the GPS system was closed down tomorrow and we would have to go back to traditional navigation.

The reason is that there is many new boat owners that never learned traditional navigation.

But even me who have owned boats for 50 years and was in charge for navigation in numerous race boats before the introduction of satellite positioning, decca, and Loran
Is not 100% comfortable navigating in the traditional way any longer. Navigation skills is something that you need maintain. I’m sure the after some weeks I would feel more comfortable.

I think electronic navigation combined with understanding of the limitations of electronic charts is the safest way. I think it easier for people that have navigated in the traditional to understand those limitations. Not saying you can learn the limitations even without traditional navigation skills.

Navigation in poor visibility with fog or at night will always be much safer with digital navigation.

[RaymondR]

I suspect that it does not much matter whether we, the recreational boating sector, decide one way or the other, the means of traditional navigation ie. printed paper charts, ephemeris tables etc. are probably going to cease to exist not to far in the future as commercial interests and the military cease using them.

I still carry a range of paper charts sufficient to take me all around the continent of Australia because I already had them from the times before computer, plotter and MFD navigation. However if I was starting cruising today I seriously doubt whether I would have them as the cost alone being prohibitive.

As to the discontinuance of printed charts in response to the challenge of digital, I recall reading somewhere that the Australian hydrographic office has discontinued printing many of the large scale charts as there is no longer sufficient demand for them. For my part I have noticed that a number of the chart shops I once frequented have ceased to exist.

There is definitely a romance attached to the paper chart and nothing better than spreading one out for a "where to next" session but if one is that way inclined I'd lay in a stock now as I suspect the opportunity may not exist much longer.

[conachair]

Originally Posted by Paul L

Actually this is the condition where having a Radar overlay on the chart display on an MFD does tell you if the chart is aligned to reality or not. When we arrive in a new area I always do a quick radar overlay display to verify that the chart datum is valid.

As is checking satellite image sources from SasPlanet as chart plotter files or in sasplanet itself. A few keyboard shortcuts and you can flip between various Sat images and navionics/cmap. Very useful, sat images can be great when cruising

[jtsailjt]

Originally Posted by Benz

^^But once again, this last guy and Pizzazz won't address the obvious fact that where charts are not aligned with the geoid, which Ping posted a picture of, no amount of cross-checking plotters and ipads and radars will keep you off the rocks. Perhaps they have the good fortune or foresight to sail only where the charts are well-aligned, but I cruise in more places where they are not than where they are.

If you're cruising in an area where the charts are misplotted, doesn't that apply equally to paper charts as it does to digital charts? The chartplotter knows your latitude and longitude and height above sea level and it knows the latitude and longitude and height of the rocks. Unless somebody fouled up or didn't have the technology to plot the rocks accurately during the survey (long ago), then your chartplotter will show where the rocks are just as your paper chart will. You might have to steer a slightly different course to get there than you first thought but that's true for paper charts as well if the variation has changed significantly enough to be noticeable. In most sailing conditions other than flat calm, I can only steer plus or minus about 5 degrees anyway so I'm always correcting to get my course line pointed to where I want to go. It's MUCH easier to stay updated on my constantly changing position, and to know what might be an appropriate correction using up to the split second info available via digital means than it is to take time out to try to take a celestial shot, do the math to figure out where that puts me, then compare where I thought I'd be at the time of the shot, guess how accurately I've been steering my intended course and also guess whether my new shot or my DR plotted position is probably more accurate, and then figure out what course to steer in order to get myself back on course and then to know when I am back on course.

BTW, you say you sail more often where charts are not well aligned than you do where they are well aligned and I'm wondering where you've been doing most of your recent sailing that would cause you such problems? You must now be a VERY long ways from Bristol RI in a place where there is cheap enough Internet access to fairly regularly post on this forum, but in a place where the charts, or at least digital charts aren't accurate enough to safely navigate by. And you say it's like this more often than not. Where are these places? How far off are they and how much worse accuracy does that yield than when you determine your position from a celestial shot aboard a moving sailboat and then use DR until you have an opportunity to take another celestial shot and plot that position? Also, on a 31 foot sailboat with 4 people, how do you find room to carry all the detailed paper charts to navigate to all these remote spots so you have accurate information (more detailed and more accurate info) than on a chartplotter?

[mvweebles]

When I was delivering, many of my deliveries were teaching deliveries with the owners inboard. I've noticed over the years that, in my opinion, most boaters spend too much time looking at their chart plotters and not enough time looking around them for situational awareness. ENC charts, like Google maps, are good for very close range but deny the operator a overview to develop a memory signature for the area within a couple miles or so around your boat--for those who still use highway maps because Google maps is too narrow, you know exactly what I mean. Mostly applicable to channels and such vs open waters.

Looking at charts (and I'll include raster e-charts) allows you to see patterns in ATONs, especially at night so you can navigate more accurately in a channel via visual vs chart plotter. ENCs often have too much data and not enough information, and there is little filter to denote accuracy.

In summary, I guess I'm saying both electronic and paper (or raster); and neither - spend more time looking at all the information you have (the lay of the land around you) , not just a chart.

[requiem]

Originally Posted by Benz

But once again, this last guy and Pizzazz won't address the obvious fact that where charts are not aligned with the geoid, which Ping posted a picture of, no amount of cross-checking plotters and ipads and radars will keep you off the rocks.

Errors in georeferencing, or simply mismatched chart datums, aren't a new thing. Many users of the USGS topo maps on land are used to checking the datum as current charts use WGS84 but many classic or 3rd party ones are stuck on NAD27. Similarly, I'm used to marking current declination values on paper maps.
Had I the need to use older charts I'd be marking the current variation on them as well.

Even if the chart datum isn't provided or incorrect, It's not too difficult to check in advance by comparing satellite photos, or on scene by comparing radar returns. As long as people are aware of the various opportunities for error and verify such details as part of their passage planning this shouldn't be an issue.

[El Pinguino]

Originally Posted by jtsailjt

But do you use a GPS chart plotter that’s 30+ years old that doesn’t correct for changes in variation and with digital charts that haven’t been updated in all that time? Very doubtful. Changes in variation are no bigger danger to digital navigators than they are to those who use paper charts, probably less.
...............

Yes..... well pretty much.... CM93 on the original burglebrand system on a second hand Acer.... don't think it does 'magnetic'.

Not sure what the Isailor on my Ipad does...... I know it doesn't want to cross the dateline..... I suspect a 'flat earther' had a hand in its development...

[Oceansailor]

Originally Posted by jtsailjt

If you're cruising in an area where the charts are misplotted, doesn't that apply equally to paper charts as it does to digital charts? The chartplotter knows your latitude and longitude and height above sea level and it knows the latitude and longitude and height of the rocks. Unless somebody fouled up or didn't have the technology to plot the rocks accurately during the survey (long ago), then your chartplotter will show where the rocks are just as your paper chart will. You might have to steer a slightly different course to get there than you first thought but that's true for paper charts as well if the variation has changed significantly enough to be noticeable. In most sailing conditions other than flat calm, I can only steer plus or minus about 5 degrees anyway so I'm always correcting to get my course line pointed to where I want to go. It's MUCH easier to stay updated on my constantly changing position, and to know what might be an appropriate correction using up to the split second info available via digital means than it is to take time out to try to take a celestial shot, do the math to figure out where that puts me, then compare where I thought I'd be at the time of the shot, guess how accurately I've been steering my intended course and also guess whether my new shot or my DR plotted position is probably more accurate, and then figure out what course to steer in order to get myself back on course and then to know when I am back on course.



BTW, you say you sail more often where charts are not well aligned than you do where they are well aligned and I'm wondering where you've been doing most of your recent sailing that would cause you such problems? You must now be a VERY long ways from Bristol RI in a place where there is cheap enough Internet access to fairly regularly post on this forum, but in a place where the charts, or at least digital charts aren't accurate enough to safely navigate by. And you say it's like this more often than not. Where are these places? How far off are they and how much worse accuracy does that yield than when you determine your position from a celestial shot aboard a moving sailboat and then use DR until you have an opportunity to take another celestial shot and plot that position? Also, on a 31 foot sailboat with 4 people, how do you find room to carry all the detailed paper charts to navigate to all these remote spots so you have accurate information (more detailed and more accurate info) than on a chartplotter?

You are correct that the paper charts are as much out of alignment as the digital charts.

But when you navigate in the traditional way you estimate your position in relation to land, lighthouses etc. The alignment is not so important. As soon as you do not do visual navigation the alignment error will be a problem.

When you do electronic navigation your position will be placed on the wrong place on the chart as the chart is not aligned.

[El Pinguino]

Q?

What is more important?

Your Lat/Long or your relationship with terra??