Navionics vs C-Map for French Polynesia / South Pacific ?

[tracker_46]

Just looking for a budget e-charting setup as backup to paper charts for an upcoming South Pacific cruise.. Because of my budget, I was considering going with SOB Digiboat and C-map charts (the only charts supported by digiboat). However, the one region where I'd really like to be able to reference the electronic charts is the Tuamotus..... Unfortunately I just read that C-map charts were highly innacurate in F. Polynesia... Has anyone heard whether the new C-map MAX editions have resolved the accuracy problem? What about other areas like Tonga/Fiji?
On the other hand, I had read that Navionics charts were VERY accurate in French Polynesia due to the fact that Navionics had integrated/purchased the French charts and integrated them into their electronic product. Has anyone heard of a budget chartplotting program for PC similar to Digiboat that instead uses Navionics?
I'd love to hear from anyone who has had experience with C-map, Navionics, digiboat, etc in the South Pacific. Any recommendations?

[Rangiroo]

I have just come through the Sth Pacific last year and I used Navionics charts in a Raymarine chartplotter. They were GREAT!!!!! There are two places they were inaccurate in 13,500 miles of sailing. They had me on the hill in Luperon Harbor in the Dominican Republic and they had me on the reef on approach to Apia Harbor in Samoa. Otherwise they were DEAD accurate!
Fugawi is great navigation software that uses Navionics charts. Fugawi GPS Navigation and Mapping Software Homepage

Whatever else we might think of the French they certainly have there charts and navigation aids spot on. In the Tuomotus all the passes were clearly marked and easy to see however I would NOT sail around there at night without an excellent chartplotter and trusted charts. They are not called the Dangerous Isles for nothing. During the day you can see all the atolls and lagoons.
I would HIGHLY recommend spending LOADS of time there and very little time in Papaeete. The pass dive in the nth pass in Fakarava is absolutely astounding!!

Good Luck!

Michael

[donradcliffe]

You should have a private message

[Eric50]

Thanks Rangiroo for the comments ;-).

In addition about french maps (paper ones):

A lot of indications are given, in term of accuracy, in the legend or in the "inserted areas" (smaller charts in the corners) that detail the density and dates of the hydrographic surveys of the charts.

Actually, some charts (or some parts of the chart) are based on very old survey (specially in remote areas like polynesia) and the density of the measurment can be very poor (it is shown by the number of depth indication).

This can lead to a "not so accurate" document and when you sail in theses areas of the chart you must stay alert and navigate with caution (although, most of the time the chart is OK for our purpose).

A good watch in the spreaders is one of the solution in tricky passage for example.

From this year, all french paper charts shall be under WGS 84 referential, FYI.

The ones that used to be under ED50 will not be edited and sold anymore.

Another (anecdotic) info is that french charts are usually french for the french areas....and french charts covering non-french areas are usually reproducing charts form the local authorities as all the hydrographic offices are exchanging their library to cover all the world easily.

This is another point to take care: the GPS referential : make sure you are taking in account the differences that are coming from the GPS referential applied on the paper chart (which can not be WGS84, but something else with non US charts) while plotting a coordinate with a GPS that is usually under WGS84.

It is not recommanded, however, to change the GPS referential of your GPS - but to stay in WGS84, as this "correction" is an average and not absolute for the location you are.

It is better to "manually" add the paper chart corrections while plotting and more accurate.

Last but not least, only the ECDIS systems are officially approved and garantueed as electronic charts and, normally, without errors.

It means that all the electronics charts under commercial brands can have some errors (Garmin recently call back some of their products for that reason) or inaccuracy and must always be counter-check by other navigation means or procedure.

Hope this will help.

[tracker_46]

Great info, guys, thanks a lot! So far, Navionics 2, C-Map 0....
In reference to Eric50's recommendation to take notice of the datum (or referential) of the French or non-U.S. charts when using a GPS set to WGS84:
How does one figure out the manual (paper) correction you'd have to make to a WGS84 GPS coordinate in order to plot it accurately on a non-WGS84 paper chart? I assumed that changing the datum on your gps to match the one on the chart was the easiest way to go, but it sound like that's not a good idea. How do I go about figuring out how to calculate the correction? Any good references you can point me to on this topic?

[Eric50]

The correction are normally indicated on every paper chart under international format and based on a different datum than WGS84:

They usually are indicated as: add (or remove) so many ' and " N or S for latitude, and the same (E and W of course) for longitude.

Of course most of the time correction are less than a minute.

It brings me to the next question about changing the datum on the GPS:

You have to know that the correction setting in the GPS is made or chosen by the manufacturer and that geographical differences from one datum to another are not constant in the area covered by one of these datum.

For example, the correction setting between ED 50 and WGS 84 are usually the ones for the difference between the center of ED 50 (which is roughly the center of Europe area) and the same location indicated under WGS 84.

But this difference is not constant and the more you are away from the center, the more the difference varies and also...increase!

That is why it is better and safer to apply the correction given on the paper chart, as these correction are the EXACT difference (at the map's location between, verified by official survey department) the 2 datum and not a theoritical and "average" one as the one chosen by the manufacturer of your GPS.

It means also, that the offset settings are not the same from one manufacturer to another one for the same correction between 2 different datum...

As usual for navigation, chart plotting and tricky areas, it is always recommanded not to believe 100% the GPS and let him (with the pilot) fully controling the ship's course.

A permanent visual checking in difficult area and cross-checking between what you see at the chart table and outside is the only way to ensure a safe journey between rocks, stream...

Hopefully, chart is a domain under huge progress and development, accuracy is becoming so high that it is now beyond all our simple sailor's dream and should harmonize and correct for everybody very soon all over the planet.

Thanks to USA and their GPS system for that.

[SailSurfROAM]

Hi

Looking for any recent preferences on this topic or should we stick with tracker_46's score of 2-0 to Navionics?

I have Raymarine gear built into the boat so have the choice of C-Map or Navionics.

We also run OpenCPN and use the google earth images nested but want to still run chart-age on the Raymarine gear.

Cheers
Mick

[Paul L]

We used up to date C-MAP charts through the S. Pacific in 2015 and they were excellent.

[SailSurfROAM]

Thanks Paul L

Score at 2-1. Positive feed back for both camps. Thats good.

Cheers
Mick

[Littlechay]

So far C-Map from Jeppersen has been spot on for me.

Generally I find that if you are off-piste C-Map trumps Navionics. If you follow the crowd then sometimes Navionics are ahead, not so much with the charting but with info on facilities etc..

Disclaimer. I don't have Navionics on my own boat so can't directly compare here in Polynesia.

Chris
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Tweed's World | A high latitude sailor preparing for tropical cruising