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Old 29-11-2015, 10:29   #1
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Navionics charts (maybe all chartplotter charts)

No, this definitely is not an ad for Navionics charts...

I frequently find that we are positioned well off what I know to be our location. I also know of more than one boat which has been lost relying on Navionics charts in the Bahamas, including eyeballs on 2 of them. OTOH, I have seen other companies' charts referenced with pictorial evidence of the same behavior.

I routinely use three different (plus eyeball 1.0) programs - the Raymarine C120C plotter, which uses Navionics charts, OpenCPN (sometimes also the Cap'n) and hard charts (Explorer in the Bahamas, because I don't trust any of them; OpenCPN and Cap'n, e.g, using NOAA charts, have placed me on the second row of marinas when I'm on the face dock fueling, e.g.).

So...

Is it Navionics, all charts, our GPS system, or something else at work which has you wondering if strict adherence to the magenta line,or if in otherwise unchannelled water will, in fact, have you running over hard and/or sharp things?
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Old 29-11-2015, 13:33   #2
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Re: Navionics charts (maybe all chartplotter charts)

It depends on where you are. Certain cartographies are better in certain areas. As you mentioned, Navionics is awful in the Bahamas - particularly the less travelled places. CMap, on the other hand, contains the Explorer Charts (along with their routes and anchorage data) and is dead-on accurate (as far as they go). Garmin's iPad app also contains the Explorer Charts, routes and data, and I think they are available on Garmin's chartplotters too, for additional cost.

In other parts of the world different cartography shines/sucks. For example, in parts of Central America, Navionics is pretty good but Garmin will get you into loads of trouble.

The chart plotter or computer program itself has nothing to do with the accuracy - it is the specific charts that are at issue.

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Old 29-11-2015, 13:37   #3
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by colemj View Post
It depends on where you are. Certain cartographies are better in certain areas. As you mentioned, Navionics is awful in the Bahamas - particularly the less travelled places. CMap, on the other hand, contains the Explorer Charts (along with their routes and anchorage data) and is dead-on accurate (as far as they go).


clip...

Mark
I previously had Cmap (the C series is only navionics) and formed my distaste for Navionics, as, as you say, the Cmap versions were right on, down to the placement of the boms...
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Old 29-11-2015, 15:43   #4
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by skipgundlach View Post
I previously had Cmap (the C series is only navionics) and formed my distaste for Navionics, as, as you say, the Cmap versions were right on, down to the placement of the boms...
CMAP stinks in some venues too. My solution is to have both aboard. Relatively cheap to do these days with the Navionics & Plan2Nav apps.
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Old 29-11-2015, 15:49   #5
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Re: Navionics charts (maybe all chartplotter charts)

In this situation, it tends to be a problem with the chart origin compared to WGS84. And it doesn't matter which product you use if they are based on the same charts.

While details on a chart are generally accurate in relation to each other, the original location of the chart origin may have been inaccurate, especially if they are based on old sureys. I've seen it with Navionics, Garmin and CMap.

Several local examples come to mind ( I won't mention which product in each case):

1. There is an island near here lying at the end of a reef. It's a popular fishing spot and a rounding mark for longer inshore/offshore races. As we zoom in and out on our plotter two different maps are used and the island "moves" a couple of hundred meters NE/SW.

2. Sailing down the coast from here, initially the plotter is spot on. Once we get a hundred miles or so down, it changes and our position is offset about 700m (!) to the ESE.

3. Entering Sewa bay on Normanby Island requires a dogleg through a channel about 100m wide. Our GPS track showed us cutting across the land a couple of hundred meters to the East.

Many chartplotter allow you to offset your chart. If you are going to be in an area for a while it's often a good idea to stick yourself in a known spot such as alongside a beacon and adjust the chart offset to local conditions. (Don't forget that you have done so when you move to another area ! )


IOW, there is no subsititute for the mark one eyeball, a hand bearing compass, a depth sounder (FLS is especially useful in some areas) and plain common sense in interpreting your chartplotter display. Never believe what it is telling without alternative evidence, especially if it is an area you haven't sailed in before.
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Old 30-11-2015, 09:23   #6
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Re: Navionics charts (maybe all chartplotter charts)

What about this:


Could it be that the GPS system (US owned) is set off track. I noticed this years ago when in London the Metro attack's were coming/going on. And on last 12 november the day before the attacks in Paris I also noticed my GPS was off track.
Yes, in this case it doesn't matter what program or charts you are using.
This might be a complete other problem than you mentioned 'skipgundlach'. In that case please leave my comment for what it is.
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Old 30-11-2015, 09:28   #7
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by Horus View Post

clip...


This might be a complete other problem than you mentioned 'skipgundlach'. In that case please leave my comment for what it is.
??? I don't see a comment...
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Old 30-11-2015, 09:33   #8
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Re: Navionics charts (maybe all chartplotter charts)

About the off track GPS position.
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Old 30-11-2015, 09:36   #9
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by Horus View Post
About the off track GPS position.
I wouldn't try to alter anyone's comment, in any event. I figure there are probably ways, should the US and Russia determine it advantageous, to alter output on GPS satellites; witness the removal of the error correction block, years ago...
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Old 30-11-2015, 10:08   #10
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Re: Navionics charts (maybe all chartplotter charts)

I was informed by the salesman prior to buying .you new Garmin touchscreen that all of the manufacturers have terrible performance on the Northern Peninsula here in Newfoundland. We soon discovered this on our voyage there this summer. A friend had advised me to print the French charts from the provincial museum website as they are the best he had found in his years of cruising along that coast. The originals date from 1859-60.

It definitely seems they are all only as good as their source material. My cockpit plotter is Lowrance and suffered the same inaccuracies.
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Old 30-11-2015, 15:14   #11
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by Horus View Post
What about this:


Could it be that the GPS system (US owned) is set off track. I noticed this years ago when in London the Metro attack's were coming/going on. And on last 12 november the day before the attacks in Paris I also noticed my GPS was off track.
Yes, in this case it doesn't matter what program or charts you are using.
This might be a complete other problem than you mentioned 'skipgundlach'. In that case please leave my comment for what it is.
No, if the GPS was "off track", it would be so for every user.

Has anyone ever seen previously accurately chart positions suddenly offset by more than the normal margin of error?

(So you think the US knew about the Paris attacks the day before and tampered with GPS but didn't warn anyone? )
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Old 30-11-2015, 16:08   #12
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by StuM View Post
In this situation, it tends to be a problem with the chart origin compared to WGS84. And it doesn't matter which product you use if they are based on the same charts.

...
No, in many venues CMAP or Navionics are simply wrong. Dramatically so in many cases...not even close, not just an offset issue.

For an example, look at Sapzurro, Colombia on both. Navionics isn't even close...in anyway, details or offset. CMAP, in this case, is much better.
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Old 30-11-2015, 16:42   #13
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Re: Navionics charts (maybe all chartplotter charts)

I've posted many times about Navionics being a waste of money if you're cruising the Bahamas. And, in fact, the newer Navionics chips are worse than the older (2004) chips which had unauthorized Explorer Chart data.

I used to correspond with Navionics pointing out the glaring geo-referencing errors but have given up as they would not tell me whether the errors I brought to their attention have been corrected. They would simply say that they have a "new" electronic chart chip. I found out when I first corresponded that the "new" chip was worse than the old one. This was done by comparing my 2004 chip with their "new" chip on a buddy's boat. I now have one of their latest (2013) Bahamas chips (replaced the chartplotter and it now takes a micro SD instead of a CF card ). The old (2004) chip is still better but unfortunately I can't use it. If anyone want my 2004 Navionics CF chip it's going for a song. I should not have gotten another Raymarine but did so as all my other instruments are Raymarine.

In tricky areas I rely on my eyes, Explorer Charts and an iPad with Garmin charts.

I notice that in the past couple of years Navionics has been in Georgetown at the Regatta touting their electronic charts. My advice is that if you intend to cruise the Bahamas forget about Navionics.
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Old 30-11-2015, 17:16   #14
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Re: Navionics charts (maybe all chartplotter charts)

That is why the first rule of navigation is to fix your position by 2 INDEPENDENT sources. Checking to GPS based positions against two different electronic charts or a paper chart is better than nothing but all your position fixes are still based on GPS co-ordinates. The answer is to make sure that before you do anything critical like a night harbour entrance or rounding a point close in you check you position by compass fix and/or radar. This confirms you position and tells you the current local GPS error. Once you confirm the error you can then put more reliance on GPS for the rest of those maneuvers. There has been significant loss of life and vessels both commercial and pleasure due to over reliance on GPS. It is also worth checking the source data for charts before using them, you will be surprised how many are still based on a lead line survey from a sailing ship in many cruising areas. I am not talking remote areas either, I have seen dates in the 1800's in the Bristol channel and Irish sea!
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Old 30-11-2015, 17:48   #15
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Re: Navionics charts (maybe all chartplotter charts)

Quote:
Originally Posted by colemj View Post
It depends on where you are. Certain cartographies are better in certain areas. As you mentioned, Navionics is awful in the Bahamas - particularly the less travelled places. CMap, on the other hand, contains the Explorer Charts (along with their routes and anchorage data) and is dead-on accurate (as far as they go). Garmin's iPad app also contains the Explorer Charts, routes and data, and I think they are available on Garmin's chartplotters too, for additional cost.

In other parts of the world different cartography shines/sucks. For example, in parts of Central America, Navionics is pretty good but Garmin will get you into loads of trouble.

The chart plotter or computer program itself has nothing to do with the accuracy - it is the specific charts that are at issue.

Mark
===

Here's another vote for the CMAP charts. We use the electronic versions and they are far and away the most accurate for the places we've cruised. That includes the Bahamas, T&C, DR, Puerto Rico, BVI and Eastern Carib. Some of the NV charts are beautiful to look at but contain some really major inaccuracies. We have many track lines showing us going over dry land.
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