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  #31  
Old 02-18-2009
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I think the "special case" is nominally mid-ocean places like the Tuamotus, and so on, an area both sometimes inaccurately charted, or inherently dangerous due to charted but awash reefs and atolls.

Sable Island comes to mind, as do places like the Torres Strait, the Barrier Reef and like this: Pacific Ocean - Elizabeth & Middleton Reefs (this whole site is great for weird little islands and reefs.)

If you chart a course and keep a running fix from CN, divergences due to current or steerage (like XTE with GPS) will eventually appear and can be corrected. Sailors used to plot courses to avoid land, but GPS sailors will, by contrast, tend to want to sail past land for the visual confirmation or because it's a more direct route. "Waypointers" don't always keep a prudent offing, in my view, because so much of the navigation is left to the plotter and the AP.

Because of its greater "circle of uncertainty", by contrast, CN encourages caution and land other than the destination is ideally avoided altogether.

How do I know this? From the changing nature of boating accidents and groundings...people are very precisely hitting the same damn rocks four feet below the surface of the ocean! We've all heard about people piling into breakwalls, huge buoys, piers and the like, sometimes at speed. It's sheer carelessness, aided and abetted by precision instrumentation that itself doesn't have a stake in staying dry.

I have to wonder if some sort of cutting and pasting of lat/lons goes on instead of looking at the right charts, and manually plotting a course that gives a good offing that is clear of fringing reefs and yet close enough to get into a viable anchorage promptly.
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  #32  
Old 02-18-2009
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Valiente—

Unfortunately, too many GPS chart plotter users believe that the icon of the boat is actually where to boat is in the real world. What the icon of the boat actually represents is an assumed physical location, subject to the accuracy limitations of the satellite system being used, on a map makers interpretation of the real world, which may be based on information that is decades old. There's way too many qualifiers in that for me to rely on it. Mark I eyeball is always my primary navigation tool when in coastal waters... Dead reckoning, CN and GPS are all to be used when in open waters.
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  #33  
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Well, we are beginning to derail the thread, but that is what I was getting at: how the behaviours of sailors relying solely on GPS are on occasion premised on unsupportable or transitory data.

I prefer to think of GPS are "a really good suggestion with elements of a guess", and I don't use the plotter aspect, preferring to transfer lat/lon to a paper chart, and then to look at the paper chart, and then look out the pilothouse window, and then back at the compass, and then back out the window, and then I figure out if I actually am when I'm supposed to be.

And yet every summer you can see gloriously clean Bendytoys in Lake Ontario with a guy at the helm in a Tilley hat staring at a huge helm plotter display, more or less oblivious to his immediate surroundings.

I really enjoy sailing past such people in my monstrous steel tank about five feet away, and fouling their wind! I grin and wave and say "Nice day, skipper! How's she runnin'?" as I haul ass ahead. One guy actually dropped his drink when the shadow of my sails fell across his display.

Yeah, I'm a bit of a ***** sometimes. But it's actually a worse problem than idiots driving with a sandwich in one hand and a cell phone in the other, because of kayakers, canoeists and so on that these dopes aren't looking for.
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