One of the most popular charting sources... but can you trust it?
Satellite photographs don't always show what you need to see.
An older—but popular—option that isn't accurate in some areas.
Even NOAA chart experts will admit that all charts have errors.
This Navionics chart shows two non-existent passes at the north end of Tahanea in the Tuamotus of French Polynesia.
Navionics displays several islands to the southwest of Isla Angel de la Guarda in the Sea of Cortez, Mexico.
They don't exist.
Over on the east side of the same island, Navionics tells us there is a sweet bay offering great protection from a southerly. It's not there.
In Puerto Refugio, notice the reef in the anchorage. Which chart would you rather use when anchoring?
OK, those were some remote places. But what about Navionics in the USA? Here's Red Bluff Bay in Alaska. Notice our track as we looked for an anchoring spot. The areas that were supposed to be shallow were too deep to anchor.
Much of the SonarChart data is crowd-sourced. Do you trust your boat to someone else's depth sounder? And lots of those lines are mathematically estimated so the charts can look more accurate than they really are.
A lot of info creates clutter on the screen. The NOAA chart is far easier to use when anchoring.
Entering the pass at Taenga, French Polynesia, would you rather navigate with this?
Or this?
The post reads:
3 weeks ago I hit a large reef 1.7nm from the large marina in Denarau, Fiji. This reef is not charted on Navionics, however clearly marked on OpenCPN CM93 charts. Unfortunately visibility was bad and I didn't keep a close eye on OpenCPN. This reef was omitted from the Navionics charts. Don't trust Navionics!
(Misinformation on Navionics charts has also been cited as the cause of boats hitting the reef at the southwest corner of Huahine, French Polynesia.)
Have you used CM93 charts in Mexico? The CM93 coast is nearly 2NM west of the actual coast in this layered satellite image of Banderas Bay.
Here's the satellite image of the three atolls of the Îles du Duc de Gloucester of the Tuamotus, French Polynesia
This is Navionics.
And CM93.
They aren't there.
Zip.
Nothing.
All satellite images are not created equal.
Which of these is a more accurate image of the pass at Katiu Atoll in the Tuamotus?
Satellites don't capture everything.
Here's Roca Corbeteña near Puerto Vallarta, Mexico.
And here are three satellite images of the same area. Three different sources—Google Earth, Bing Satellite, & ArcGIS—and none of them show this rock.
Which is not that small of a rock...
Here's an ArcGIS image of Malevuvu in Fiji.
This is Bing Satellite. Not quite as good -- notice a section is missing.
And Google?
It's not even there.
Yep. Safe navigation takes effort. It's not just steering a representation of your boat around obstacles on a chart plotter. Using the wrong chart can lead to disaster.
Ceva-i-ra to the southwest of Fiji looks very different on each of these charts... and it doesn't even appear on the satellite image.
If you don't yet know how to use chart groups in OpenCPN, here's a tutorial.
Remember, your eyes are your best navigation tool.
And the best aid to navigation is daylight.
