Paper charts and chart plotters...

[idlerboat 116]

Just a reminder, what is on your chart plotter is the same as what is on most paper charts.

Do not make the mistake and think that chart plotter charts are somehow miracuously acurate....they are not.

Chart plotting companies dont run hydrographic survey ships for the benifit of their clients.

They take (up dated, if you buy the lattest) information from the local charts. This is no differant to buying an updated paper chart (the purple writing).

Many are very very old.

Chart plotter manufacturers adapt datums of various charts so that they fit "seamlessly" to a set overal datum on your screen.

Try scaling up and down on your chart plotter between differant scales in a remote location and you will see what I mean.

Dont be fooled if you are going somewhere , where there is little traffic or no comercial interest.

Both your paper chart AND your chart plotter may be wrong.

We now have the ability of systems close to aircraft....but sometimes, its safest to have a visual only landing.

[Island Time 1,235]

Yep, absolutely. Seen both wrong, by quite a bit. There is no substitute for the mark 1 eyeball!

[Grinna 2]

I would suggest that electronic charts should be trusted less than paper charts. Have you ever done a side by side comparison between an electronic chart and a paper chart for the same area?

 

As an example, try comparing the Navionics chart for the Kawau Island area with the latest paper chart. You'll find residual current symbols on the paper chart that don't appear on the electronic version. The tide diamonds on the electronic chart all have the same letter, etc, etc. There are a number of SNAFUs that I know of in just that one small area of coastline. How many others are there?

[Island Time 1,235]

That depends Grinna, you have to compare the latest paper chart with the latest electronic one. It is part of the issue with traditional plotters - it can be hard to update the charts. The better electronic charts, usually licences ones, and usually only on a PC or tablet, can be updated online via internet connection. Same as paper charts, they should be kept up to date. By the way, many electronic charts, especially raster format, are scans of paper charts, so there is no difference at all....

[NevP 0]

I would suggest that electronic charts should be trusted less than paper charts. Have you ever done a side by side comparison between an electronic chart and a paper chart for the same area?....

I can't help but wonder if this is a case of you get what you pay for and not really a digital vs paper issue. Nothing against Navionics, it seems like a great tool but don't think I would rely on it as my primary navigation. Can we really expect to get a full set of NZ charts to use for navigating so cheaply?

 

Where do Navionics get their chart data for NZ from? I'm guessing that it's not the official ENC data supplied by LINZ (http://www.linz.govt.nz/hydro/charts/digital-charts/encs). I would hope that if you have a copy of the LINZ ENC data and compare it with a paper chart they should be pretty close to identical. If not wouldn't LINZ be on pretty thin legal ice?

 

Does anyone know if the big name chart plotter brands use the official LINZ data? My guess would be that they probably do and is at least part of the reason for the price difference.

 

All just speculation on my part though. Does anyone know for sure?

[Island Time 1,235]

Navonics offer a daily chart update service by subscription. Of course you have to pay them! http://www.navionics.com/en/update-your ... nd-save-50

So, if you are right up to date, and the errors are still there, then that would be interesting.

Most companies make you agree to a disclaimer for liability before using electronic charts, or, like the Linz ones, say "not for navigation". If they are not for navigation, what's the point of issuing them?

[Grinna 2]

NevP, I'm talking about Navionics charts for the Raymarine chartplotters installed on our yacht ... not necessarily the Navionics app for smartphone/tablet which I haven't examined closely. The cards for the plotters are certainly not cheap (in the order of $4-500) and are supplied to support a piece of purpose-built navigational equipment. Rightly or wrongly, there is an expectation (despite the disclaimers displayed at start up) that the electronic charts could be used for navigation purposes in a piece of navigational equipment and a temptation to trust the information displayed by your chart plotter.

 

I agree that one shouldn't trust any chart (electronic or paper) implicitly and that there is a further caution that electronic charts are not necessarily better (and in some cases definitely not better) than paper charts so should be viewed with additional caution until you've satisfied yourself as to their functional accuracy.

 

And just to be clear, functional accuracy is different to complete accuracy. For instance if your electronic chart (or paper chart for that matter) shows a rock in position A, but you know by personal observation, experience and or general intelligence (you've eyeballed it or actually hit it) that it is actually at a position offset from postion A by, say 50 metres, and allow for that error whenever you're in close proximity to the rock, then that electronic chart is functionally accurate (i.e. it warns you of the presence of the rock) while not being completely accurate (showing the real position of the rock).

[NevP 0]

Grinna, yes I misunderstood initially. Thought you were referring to the phone/tablet apps. It does seems a little disconcerting if the Navionics charts don't display the same information as the paper/raster charts. Still makes me wonder if their data comes from the official source (LINZ) or somewhere else.

You would hope that LINZ would have checks in place so that snafus like the ones you mentioned don't get through on the official data sets, or maybe I'm just been too naive.

[John B 106]

Its something to always watch for , but since about 08 when I put my raymarine plotter in, I've only come across perhaps 2 significant errors around the gulf and up to North cape, and another 2 or 3 where rocks on the plotter chart just aren't there.( which is a default to safe isn't it.) So generally its been pretty good. Just don't try man o war passage in a white out.

 

One thing I am pissed off about it though is that when I was first quoted ,the guy at that location offered to and does keep his other customers machines updated by periodically reflashing the cards with the latest.

I moved though and ended up buying it elsewhere. When I asked about updating the chart Lustys told me to buy a new one at 4 or 500, thats it, take it or leave it. So I won't be replacing the system with Raymarine. Don't underestimate customer service eh.

 

Garmin seems to have a good reputation for general accuracy in the islands right now ( with all the eyeball back up riders of course ). Blue seas charts. They were very good in areas I went to on the two deliveries on my friends boat to Tonga and Fiji ,in fact smack on.

He was very happy with it the rest of his cruises Tonga / Fiji/ Vanuatu and Noumea.