Garbage In, Garbage Out

Recently I have been transferring my from my old gps, a vintage Garmin 76s, to a newer but still vintage 276c.

At the same time I have also upgraded my charts from Garmins BlueChart version 9.0 to version 2008.5. During this process I started to notice some anomalies which brought back some thoughts on how shocked I was when I went aground on Yellow Island in early June.

Now let me restate right from the start that my stupidity and over confidence were the number one and number two reasons why I sailed Bolero up onto the reef. I had cut the corner of Yellow Island way to close. But I made this poor choice using the following information. My tired thoughts at the time was that I had past the outer point of the reef and I could head for the marker southwest of Yellow Island.

Well the rest was history. I accepted my comeuppance with all of the appropriate emotions and swear words.

And everything would have faded into my distance memory until this recent technology upgrade. With pretty color and a relatively large screen, I had to relive my excitement on the 276c. And now things got confusing.

As ugly and stupid as my grounding was on my old 76s with my old electronic charts, it was painfully obvious on the newer 276c and 2008.5 BlueCharts.

Which show clearly show me running right over the top of the reef.

What I found was that the anomalies weren't so much due to the chart upgrade as much as they were to the coverage area. My old charts were for Seattle, US023-Seattle.

Covers from Grays Harbor to Olympia including detailed coverage of Neah Bay, Puget Sound, Victoria Harbour, Port Townsend, Bellingham Bay, San Juan Island, Orcas Island, and Blaine. Detailed coverage of the Canadian portion of the Strait of Georgia including Nanaimo, Vancouver, Gibsons, Galiano Island, and Saltspring Island
My 276c and new charts were more represent of the inside passage, CA001-Inside Passage.
Detailed coverage of Queen Charlotte Strait and the Strait of Georgia from Bull Harbour, BC to Mt. Vernon, WA, including Vancouver, Nanaimo, Powell River, Desolation Sound, the San Juan Islands, and the Fraser River, and Quatsino Sound.

Turns out that I am discovering mapping tiles and the order and priority that they get during map drawing. By digging into the actual charts I discovered that a Canadian chart, CA470366, was overlaying NOAA chart 18434. You can clearly see the differentiation in the third gps screen capture above.

So I removed Canadian chart CA470366 from the 276c and the result returned to what I had seen in my old 76s. Although much cleaner and easier to read. And still stupid.

None of this really changes anything. I was still ridiculously too close to a well marked hazard but the whole event has dragged me into trying to really understand what these electronic tools can and can't do.

In a past life I was an Aerospace Engineer and built Finite Element Models of aircraft structures. It was always assumed that those models were wrong until proven right. The assumption was that they were rife with mistakes and we worked to remove them. All along knowing that some errors would slip through in these complicated models.

That is the relationship I now have with electronic navigation. Still a great tool, but I need to dig a lot deeper and always be just a bit skeptical.