I've talked extensively with both Navionics and C-Map people. Both
companies have different approaches and each has areas that they are
better in.
Furuno is using Navionics cartography for their NN3D in Canada and
other areas outside the US. This is because the Navionics code is more
compatible with their TimeZero technology than anything really to do
with the charts themselves. Don't count out C-Map due to that.
I prefer C-Map in my area, but that may also be because I'm more
familiar with it. I ran a Raymarine E120 (Navionics Platinum) and
Furuno NN2 (C-Map) side by side last year. I found the C-Map charts
more accurate in a few situations (There were a couple spots that the
Navionics was missing a marker, 1 of those the marker was actually
missing also, but it was still on my paper chart - and most
importantly, the rock it was marking was still there).
My own observations on NN2 units is that C-Map charts seem to run
faster (redraw, panning). I had the latest firmware for the C-Map, and
the Navionics version I played with may not have been updated (although
should have been).
All that being said, I found a problem with the C-Map charts on the NN2
that wasn't there with the Navionics: When you zoom out, the detail
(nav aids, etc) disappear sooner on the C-Map NN2 than any other
plotter. I compared my NN2 display to a Standard Horizon CP300 and
CP500 and I was able to see nav aids at 12 or 16 NM zoom (can't
remember which). I was only able to see them at the 4NM range on the
NN2. With the Navionics version if the NN2, the display was similar to
the Raymarine at different zoom levels (although faster than my E120,
sorry I couldn't resist).
You have a few options for your situation:
1. Go do a dealer and check both out (the best option if available). If possible try both on a NN2 unit.
2. Call Navionics and C-Map and get them to send you some screen shots of various areas you know well. Compare them
3. See what's popular in your marina. The boaters around you will
generally know what's best, but ask a bunch of them. Somebody will have
tried both and have some opinions.
You also need to look at the feel of each chart. You may simply prefer one.
Heres's the really big technological difference: Navionics has taken
the different paper charts (at different scales) and stitched them to
one single chart. You won't see chart boundaries or anything like that
(as you will with C-MAP). It's a more seamless, easy to see format. The
problem can come in when stitching charts of different scales, the
accuracy can be compromised. I don't think there is any flaws in the
Navionics technology, it's likely more a problem with accuracy of the
original charts.
The C-Map technology pts all the different scale charts on the card.
When you change scale, you may also be changing the actual chart you're
viewing. I prefer this because it's an acutal representation of the
paper chart. Many don't like it because it can leave a discontinuity
between different charts (you'll sometimes see half an island on your
C-Map chart because it crossed between 2 charts and they were at
different scales).
Try both and see.
You can change your navnet from navionics to cmap or back. I bought a
navionics version because I wanted to see what it would be like (I'd
always had Cmap plotters). I didn't like it so had it switched to cmap
(the chart door still says navionics).
Setting backup is really easy also. Backup all your routes, waypoints
and marks. After you've switched, restore them. It works.
(PS Furuno has recently released another update for the navnet units -
I can't remember the version but calling them will get it). Make sure
the unit you buy has the latest update or get it updated before you
install. It made mine faster.
you can download cmap tools from the below link
http://cmap.ihmc.us/download/
thank you
good luck