The Offshore Voyaging Reference Site

Electronic Chart Dangers

It seems like every time a new version of an electronic charting program comes out the developers have added another way to view the chart: 3D, BathyVision, whatever.

These features look cool and using them is tempting, but they can also be dangerous.

Here’s an example:

Last summer we were meeting our friend Ed (he of the Watt & Sea) in one of our favourite anchorages.

We got there early and he texted us his expected arrival time. I texted back:

Me: Great. Watch out for the rock in the middle on your way in. It really is there, impossible to see, and bigger than charted. Go right over the port hand side close to the moored sailboat.

Ed: Don’t even see a rock on the Navionics chart, so I will cheat heavily to port on the way in?

I was stunned since the rock is clearly shown on the charts and Ed is an experienced, prudent cruiser, and no fool.

Later we talked about it and he sent me the screenshot above. There are two dangerous “features” at work:

  1. The red crowd-source marker is obscuring the tiny rock symbol.
  2. Ed was using what Navionics calls “Sonarchart”, which produces a contour-lines visualization representing depth.

OK, I know, we can argue that Ed should have seen the 5-meter contour and then clicked on that crowd-source symbol or turned that layer off, yada, yada, yada.

To which I say, bullshit! It’s always easy to criticize others from the safety of an armchair, but I believe the issue is that the screen that Ed was looking at is hard to read and counterintuitive.

The problem is that these new ways of showing charts actually show too much information and most of it is extraneous to safe navigation.

Let’s dig deeper and in the process figure out the benefits and drawbacks of various chart presentations: