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Old 15-05-2019, 15:46   #121
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Re: Another Navionics Victim in Georgetown

Originally Posted by FreeSpearit View Post
Check it out ya'll! Navionics just created a really cool way to see where changes are occurring to the charts via a heat map!

Here is the blog about it with some info:
and here is the heat map:
You can scroll around and zoom in and out to look at the density of changes to the charts anywhere in the world. Really cool!

Here is a heat map of the last 2 years (apparently the charts being used during the accident referenced in this thread had not been updated in over 4 years so you can imagine the number of changes that have occurred to the charts when you see the number of changes just in the past 2 years.
Looked this "heatmap" and it seemed pretty useless. If I understood correctly the heatmap puts a dot on the map at places where the charts are updated? Might be more useful if the heatmap would link to actual chart updates.

Also I see thousands and thousands of updates out where the water is hundreds or even thousands of feet deep. Not sure how useful that information would be for anyone except submarine captains.
The water is always bluer on the other side of the ocean.
Sometimes it's necessary to state the obvious for the benefit of the oblivious.
Rust is the poor man's Loctite.
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Old 15-05-2019, 16:00   #122
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Re: Another Navionics Victim in Georgetown

I was in Georgetown harbor that night the French cat hit the reef, I think it was a few days before regatta. It's a great little reef to take the kiddos snorkeling, and we had just a few days earlier.
The navionics I had on my chart plotter, iphone and my iPad made it very very clear there was no route there.
I am sorry for his bad luck, but if there was ever a place to call Mayday and get help it is there, the cruising community in Georgetown is fantastic, my kids like to go back there just for the Cruisers Net Radio show. I hope he gets back to sailing soon!
"We can choose what we learn but have little or no control over what we forget, fill your head carefully" Dr. R
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Old 15-05-2019, 22:29   #123

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Re: Another Navionics Victim in Georgetown

The "passages" shown on the chart images are definitely steel boat territory for the adventurous and then with tide equal to draft plus 0.3m.

The paper charts I used to use had a reliability diagram with an explanation of how the estimate of reliability was arrived at. I don't recall that they had any guarantee that they had identified every rock and shoal. What the explanation provided was the details of the bathymetric survey such as the number of survey lines carried out. The cost of identifying every rock and shoal would be enormous.

That being said there are a set of charts of the Western Australian coast between Bunbury and Geraldton which were published by their Marine and Harbours Department which did a very good job of it. However it used to drive me nuts having to change charts every hour or so. I think they used a combination of bathymetric and aerial and satellite surveys to compile them, there are very few rivers and the water is very clear in that area of coast.
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