Electronic chart detail

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kalanka

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I was at the point of buying an SH plotter with the C map "megawide" chart for western European coasts. The local chandler helpfully put the cartridge into a demo plotter for me to play around with.

I looked at a couple of points of interest, one of them being Lybster Harbour in northeast Scotland. This is a small but excellent harbour with a narrow entrance that can be challenging in certain conditions.

The chart clearly shows a light, presumably at the pier head, but there is absolutely no detail of the harbour walls, the preferred line of approach or anything that could aid getting in. Zoom right in and all you get is a large image of a vague inlet.

The assistant confirmed that there was nothing wrong with the loading of the cartridge and sought further advice. This was that I would need to buy another electronic chart.

"Seems rubbish" said the assistant, and I agree.

Can I only trust the electronic chart for big harbours and anchorages?

Am I expecting too much? I carry pilot books and paper charts in some quantity but it is hardly practicable to do this for a chart area extending form Portugal to Greenland.

Is there an elimination of detail on the wide area charts compared with local charts?

Are Navionics or others any better?
 
kalanka said:
Can I only trust the electronic chart for big harbours and anchorages? ...
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C-Map charts are good, but electronic charts are only as good as the data they are derived from; for something like this you may have to rely on the additional information given in a pilot book. Note that you can get more info on the light by putting the cursor on it.
 
I think the answer is what ever you buy be it a chart or a compass ther is allways the proviso that it is an aid to navigation and you should allways use other sources to check your position and course.

I had an experience when I first made a trip from Milford Haven to Kilmore Quay for the first time. Kilmore quay is a smaal harbour and marina, and my boat is an Ebtide 33 which can be impossible to reverse most times. It was a Sunday evening and I called up the harbour master to check that a berth was available for me to use. I got no reply so to be on the safe side I anchored in the lee Of a small Island just off shore. When I entered the harbour on Monday morning after speaking to the harbour master By eyeball MK1 Nav I found that the track my boat took was me over the end of the harbour jetty. The harbour is out of position by approx 80 metres.

So the answer is go carefully out there.
 
I guess the question is, what does the most detailed Admiralty chart (not private, local, or pilot book chartlets) show? I would expect C-Map to have everything that official charts have, but maybe I'm wrong?

Pete
 
kalanka said:
Is there an elimination of detail on the wide area charts compared with local charts?

Are Navionics or others any better?
Click to expand...

You'll find that "Local" cartridges often include larger-scale detail, compared with "Mega Wide" cartridges. If you look at the C-Map website, it lists every chart incorporated in each cartridge, together with chart scale data. You'll see that the "Scotland North: East Coast" Local cartridge has much more info on that area than the Mega Wide cartridge.

Navionics, etc, all work in the same way.
 
I don't really use electronic charts but I did many hydrographic surveys 'in my time'.
I do worry sometimes when I see users enlarging charts beyond their original scale and issuing comments like" we can just pass that obstruction with a couple of yards to spare".
I know it would clutter up the image but it would be nice to see some indication of the real ( as surveyed) scale of the chart displayed.
 
pcatterall said:
I know it would clutter up the image but it would be nice to see some indication of the real ( as surveyed) scale of the chart displayed.
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Agree absolutely, in opencpn when one zooms in in raster charts beyond a certain limit the indication "Overzoom" appears, which is very very senslble imho

I don't know if it is the case with vector charts in opencpn but it should not be too difficult to implement
 
There are areas on the Scottish East Coast where yachting charts are not produced so perhaps the electronic chart people follow their paper example and leave out the detail in those areas where there is 'no call' for it.
 
Forgive me, your expectation of an electronic chart (and I am no fan) is a little optimistic. The best scale Admiralty chart for that area is 1-200,000 - chart No 115 for Moray Firth - last reissued on 30.12.2004. You are not going to get any detail of such a small harbour at that scale and if the Admiralty doesn't have it then the electrickery chart makers won't have it. There be other reasons to reject electronic charts but a lack of detail for this harbour is not one.
 
Don't know if it's just a Raymarine thing or what but when you attempt to zoom in too far (ie beyond the scale of the available mapping) on our plotter, then you just get a cross hatched display with the message 'no chart data'. Sometimes, continuing to zoom in will reveal a further chartlet of harbour details at say 1:5000 scale; more usually, nothing but the hatched pattern.

Anyway, we usually look up a number of different bits of info before heading into a new location: pilot books, paper and electronic charts, google maps and google earth. That helps to build a more complete picture of what we're heading into and what the hazards are before we make a fraught approach to what may be a tight location.
 
Roberto said:
Agree absolutely, in opencpn when one zooms in in raster charts beyond a certain limit the indication "Overzoom" appears, which is very very senslble imho

I don't know if it is the case with vector charts in opencpn but it should not be too difficult to implement
Click to expand...

It is the same with vector in OpenCPN as well, 'OVERZOOM'
 
VicMallows said:
However the Google Earth imagery for Lybster Harbour (and all that coast) is stunning!

If I were sailing that area, I would certainly have it cached on the laptop (so it works offline) and with a GPS overlay.

Vic
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If you use Polar View on a laptop, (£55 with all Uk AVCS charts) you can display images - such as captured Google sat images. You need to geo reference them which you can do using Polarview to get co ordinates at 3 or more points.

You can then have the chart overlayed on the image.

(There is no detail on either the ARCS or AVCS)

I
 
I suspect you are expecting too much from your chartplotter? :confused:

I have added two images, one is a screen grab from Google Earth of Lybster Harbour and the other is a frame from my 12 inch Garmin chartplotter of exactly the same area. I tried to get the images of a similar size but as you can see, even Garmin have little detail even stating the danger area is about 500 feet off shore with no detail of the harbour and even the 'lighthouse' seems to be inshore and not on the pier/jetty?
 
I will again pass comment about Arisaig Bay-the origional detailed Admiralty Chart was drawn in the 1860s but the chart was withdrawn from publication by the late 19th century because the Admiralty was unhappy with it.
As a result most of us based here use copies of the origional chart.
However some if not all Chart Plotters show what they claim to be a detailed chart of the bay.
Their only source is the smaller scale chart Point of Ardnamurchan to Sound of Sleat!
 
ianj99 said:
If you use Polar View on a laptop, (£55 with all Uk AVCS charts) you can display images - such as captured Google sat images. You need to geo reference them which you can do using Polarview to get co ordinates at 3 or more points.

You can then have the chart overlayed on the image.

(There is no detail on either the ARCS or AVCS)

I
Click to expand...
Why use Google Earth and not satellite view from Google Map. With a GPs receiver you will have a plot of your location too

TS
 
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