What is your preferred method for checking your nav gear for error?

[Stumble]

Originally Posted by conachair

.... "original paper chart data "

If the last survey was 50 years ago then that's what you're stuck with.

Something sounds odd if the paper charts are out compared to cmap with the latest NTM's applied...

The digital charts are pretty much exactly what the paper charts showed, I have never known the two to differ. The problem is that many paper charts haven't been updated in 100 years or more.

It's the underlying data that's the problem not the representation of it.

This is why google earth is so interesting, it's all new data. But obviously doesn't have much depth data.

[Pelagic]

Originally Posted by Stumble

This is why google earth is so interesting, it's all new data. But obviously doesn't have much depth data.

But isn't keeping the boat floating, one of our primary objectives[emoji1]

Seriously, the detailed coastal charts with depth contours are accurate for all anchoring purposes except for geostainionary datums.

I guess we soon will have them synchronized with Google Earth, but still having a 'corrected' Radar and Sounder' will be required if going in at night.

[Paul L]

Originally Posted by conachair

Aren't the inaccuracies more likely to be from the original paper chart data on which digital charts are based on?

And again, this is where Google earth images as kap files can be very useful.

The the older charts were drawn to different chart datum than the world model that GPS uses, WGS84. There are hundreds of other models that charts have been plotted to. In addition they may have been inaccurately plotted to their own datum. So taking an old chart and converting it to digital requires adjusting the datum. Errors occur in this adjustment.

You used to be able to take the paper charts that overlapped the US and Canadian border in the Puget Sound (Pacific Northwest) and the longitudes were shifted between the charts. The chart datums used on Canadian charts was differentbthan tje US charts and they modeled the earth slightly differently.

[Suijin]

Originally Posted by nematon785

On charters,lessons, and other peoples boats I have seen some really crazy irresponsible ****. Including the captain that started drinking before we even arrived at 9am. No GPS onboard other than everybody has a mobile phone. The salty guy in charge initiating a tack while a first timer is sitting on the foredeck sunning herself. deck sweeper anyone? The captain who could not stop, or turn around to save his new hat that went overboard, god help us if it were a person.

The most important piece of navigational equipment on your boat is between your ears. If that unit is faulty, none of the other equipment is going to work properly.

Originally Posted by nematon785

No deviation cards at the compass, no charts aboard of any kind, non functioning instruments, handheld gps' floating around the cockpit that only displa lat n lon, (seems useless without a chart to refer that lat lon to until you are barking for CG or tow help on the radio and they ask your position...)

I personally believe it's imperative to have paper charts on board, and know how to navigate with them. Others do disagree, but that's their prerogative. I've been on some ocean races in fact where we've broken out the paper charts to provide a better means of analyzing and evaluating lay lines and strategies.

Originally Posted by nematon785

I have tried to operate chart plotters mounted on boats that are so counter intuitive as to be literally useless (no manual available) to me while steering. even the owner was not sure how it connected to the autopilot or how to set it up for general purpose navigation, WTF knows what datum or chart the thing is set on. we just sailed by visual cues (in and out of Marina del Ray.) actually I should say we motored in and out of Marina del ray, and sailed to include one tack to turn around... Easy and obvious visuals with the giant airport.

I bet it was Raymarine...or Praymarine. :P

As others have said, 99% of the time it's the actual chart data that is wrong. But usually it is wrong in some isolated spot, where the coastline is not mapped correctly. I have both older Garmin and newer Navionics charts on my boat, and they frequently disagree about landmasses, and one of the other will show you plowing through wetlands, or on dry land. But they both invariably (and I use that word with caution) show where I am in terms of accurate lat/long.

My instrument package has it's own GPS, and if I have any doubts about the fix of my chart plotters I will check their lat/long against the instruments. I've yet to find any meaningful discrepancy.

In short, learn to navigate, carry paper charts, and a backup GPS source, and be facile in operating your chart plotter. That's all it takes.

[conachair]

Originally Posted by Paul L

The the older charts were drawn to different chart datum than the world model that GPS uses, WGS84. There are hundreds of other models that charts have been plotted to. In addition they may have been inaccurately plotted to their own datum. So taking an old chart and converting it to digital requires adjusting the datum. Errors occur in this adjustment.

You used to be able to take the paper charts that overlapped the US and Canadian border in the Puget Sound (Pacific Northwest) and the longitudes were shifted between the charts. The chart datums used on Canadian charts was differentbthan tje US charts and they modeled the earth slightly differently.

Paper charts will say what datum there are using, any gps I've used has a menu option to adjust the datum to the many available. I think it's wrong to say "GPS uses WGS84":, that's just the most popular datum nowadays and usually the default GPS datum.
So are you saying electronic charts have been created without converting to a different datum? Sounds very unlikely and very negligent if so.

Any examples?

" In addition they may have been inaccurately plotted to their own datum."
We're in agreement here, more likely source of errors IMHO.

[boatman61]

Having stood there screaming 'Stbd, Stbd, Stbd..!!!' or 'Port' with owners at the helm relying on their CP's while I'm up front doing the Mk 1...
Guys.. you carry on with your blind faith.. I'll stick to Luddite thank you very much..

[conachair]

Originally Posted by boatman61

Having stood there screaming 'Stbd, Stbd, Stbd..!!!' or 'Port' with owners at the helm relying on their CP's while I'm up front doing the Mk 1...
Guys.. you carry on with your blind faith.. I'll stick to Luddite thank you very much..

You're allowed both

[Pelagic]

Originally Posted by conachair

You're allowed both

Of course you are....but remember the Term...ASSUMED POSITION?

To me, it was always a gentle reminder that navigating equipment and even set nav aid markers are full of hidden errors.

Those who rely on their GPS Fix without Boaties visual caution are the ones who will come to grief and then try to Nerd their way out of blaming themselves for not testing thier other sensors and confirming this basic caution.

[Cadence]

Originally Posted by boatman61

Having stood there screaming 'Stbd, Stbd, Stbd..!!!' or 'Port' with owners at the helm relying on their CP's while I'm up front doing the Mk 1...
Guys.. you carry on with your blind faith.. I'll stick to Luddite thank you very much..

I can recall yelling to the wife starboard, go right, pull the f-en tiller to you. In between jetties and seeing a red and green on a container ship in pouring rain ain't fun. They probably could not see my Clorox bottle and if they could couldn't do a thing about it. Thank God I went forward. We might have been chum.

[Paul L]

Originally Posted by conachair

Paper charts will say what datum there are using, any gps I've used has a menu option to adjust the datum to the many available. I think it's wrong to say "GPS uses WGS84":, that's just the most popular datum nowadays and usually the default GPS datum.
So are you saying electronic charts have been created without converting to a different datum? Sounds very unlikely and very negligent if so.

Any examples?

" In addition they may have been inaccurately plotted to their own datum."
We're in agreement here, more likely source of errors IMHO.

The datum conversion errors used to be a lot more common. Think digital charts even as late as 2000. There are still paper charts in more remote areas that have an unknown datum, and ones charted to a known datum but one or both axis are offset to that datum. Trying to accurately put these into digital form is more of a challenge.

WGS84 is the reference system for GPS. You can, of course, convert it to any other datum.

[rwidman]

Originally Posted by nematon785

........... What method do you fine folks use when the rubber meets the road out there to check you nav gear? how often do you double check it?

I look at the screen when passing a charted buoy or other navigation aide. I double check whenever I think of it which is not often.


No sense making things more complicated than they need to be.

[a64pilot]

Originally Posted by clownfishsydney

If you are showing your track on the chartplotter, then it should be obvious if all of a sudden the GPS goes wacky as the track will have a strange jump in it to left or right or forward or back.

It might, but I doubt it, because it would have to "know" about the error to display a shift in course

[Lepke]

I have found gps not as accurate as advertised. Just cuz it says your there, doesn't mean it's true. On the ocean it usually doesn't matter. In restricted waters and confined anchorages, I use a sextant and three armed protractor. In tight anchorages I like to use, I've re-charted using that method.

[SV Windrush II]

Before I left the US I listened to the advice of veteran sailors and read all the online forums telling me I better not only have but use paper charts sailing to the Philippines and most all the people I talked to were saying how inaccurate electronic charts are and I could not depend on them for navigation.
All I can say is, my experience for the last 2 years of sailing the Pacific has refuted all what I heard and read for the most part.

The only thing that shocked me was actually how accurate my navigation software was on my tablet, which by the way gets updated often.

Sailing through the pass at Majuro Marshal Islands put the channel markers exactly where my plotter showed them to be.

Sailing through the North pass at Weno, Chuuk during a gale, I could barely see the channel light and the clump of coconut trees on the opposite side but my plotter put me right in the middle of the channel.

Going through the pass at Lamotrek, my Plan2Nav on my tablet again put me right in the middle of the pass.

After Lamotrek I used Plan2Nav for the rest of the trip, and always gave me enough accuracy when visibly checking my surroundings and watching my depth to get in all the rest of the atolls and anchorages single-handed without issues.

I always keep my eyes and ears on my surroundings and check my plotter, radar and depth as I approach, (I have all this at my helm station by the way). This system process I used every time without fail, and passed many boats beached or found high and dry on the reef as I sailed by them. I am guessing they were not using electronics by the look of the boats.

The only thing I can figure out is a lot of people are still using outdated electronics, don't know how to use them, or the wrong software for the area they are in to explain the bad experience they are having with them, or just cannot afford it, but now to get paper charts is not all that cheap either.
I spent over $1000 for my paper chart package of Micronesia and the Philippines.

Using a sextant for finding an anchorage is really courageous as even the best sextant user may get within 100 meters of your location which in the anchorage I am at right now would put me high and dry on either one side of the bay or the other. I do much better just looking at the terrain and water to drop my anchor

[Pelagic]

I think there are 3 camps in this discussion

Luddites, Googlites and the majority of us that uses the best of what is available to confirm if we are where we think we are.

In rarely visited cruising places like the Philippines, the Electronic Chart Systems have poor coverage of small harbours, so I buy or borrow the Namria detailed charts and scan the details so that I can read the detail depth gradients, which will not be on the ECS.

GPS/ECS is my primary position fixer.

But when coasting or entering any poorly charted bay, my Radar and a look at a scan of the detailed harbour chart, is my safety fixer.