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Old 20-12-2010, 11:09   #1
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GPS - The Venus Fly Trap - Chart Plotters

When I first started navigating, I was addicted to my position. Somehow I felt that if I knew my exact position, I was somehow better off than if I only knew my general location. If I knew my exact position, life was good. If I didn't know it, then I felt uncomfortable.

I learned to do GPS navigation in the Saudi Arabian desert. I had unlimited access to the Saudi Desert, and I could drive offroad from the Iraqi border to the Yemeni border without restriction. I had the Empty Quarter as my playground - it was a sand box with large sand dunes covering an area of 1200 km by 1200 km.

You have nothing to lose and everything to gain when you live as if you are great.

When I first went into the desert, I was freaked out by navigation. I wanted to know exactly where I was every moment of the time. After all, if I didn't know where I was exactly, then I was lost. Or so it seemed to me.

The longer I explored in the desert, the less important navigation became. After many years of desert expeditions, I hardly looked at the GPS at all. I might check it once a day to see how far we had come, but it didn't really matter that much. My definition of lost had shifted from being focused on my location, to focusing on my status. Being lost had nothing to do with my location. It had everything to do with whether I had enough fuel to get back to civilization. On every trip into the desert, I carried enough fuel to drive 500 to 1000 km off-road. As long as I had enough fuel, I was never lost.

My navigation consisted of heading out into the desert for a couple of hundred kilometers into what I called a navigational quadrangle. On each side of the quadrangle, there would be roads. When it was time to come out of the desert, I simply got on a small desert track and drove in a straight direction until I came to a larger desert track which I would follow in a straight direction, until I came to an even larger desert track that would eventually lead to asphalt and the way home. It never mattered to me where I was because my location was irrelevant unless the vehicle broke down or ran out of fuel. The only time the GPS was really important was if we had a rendezvous with another group of people at a specific location, or if there was a bedouin fuel tank somewhere out in the desert that we might want to use. It wasn't a problem finding the bedouin refueling spots because the desert tracks headed to those locations.

My attitude toward desert navigation carried over into my sailing navigation. On a sailing voyage around the world, it was rare that my exact GPS position was that important. It was only near land that the GPS was more important. But even near land, there were plenty of clues as to the way to go. The tracks of ships were just like the bedouin tracks in the desert. Ships are a great clue as to where you need to be heading. There are lots of other clues like sea birds, clouds over islands, and the loom of lights at night from the land.

While it is true that GPS makes it easier to reach your specific destination, the GPS and chart plotter are a Venus Fly Trap that can get you into real trouble. The reason they get you into trouble is because the novice tends to define his situation in terms of his position. He may enter ports at night and sail close to a coast because his GPS and chart plotter show him exactly where he is located. But his exact location really has very little to do with his safety.

Knowing exactly where you are located is important. But it's much more important whether whether it's day or night or how much daylight is left. It's important whether there is an onshore or offshore wind. It's important whether the weather is improving or deteriorating.

A real mariner knows his position, but more importantly, he knows what his position means when all other factors are taken into consideration.

Your GPS position and your chart plotter location can get you into real difficulty. You sail straight into the mouth of the Venus Fly Trap because you overlook what your position means.

Beginning navigators need to know their location, but even more important they need to know what their position really means - just like the navigators in ancient times who didn't know their exact position, but still reached their destination.

Dave -Sailing Vessel Exit Only
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Old 20-12-2010, 11:19   #2
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Several excellent points.

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Old 20-12-2010, 11:23   #3
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GPS says you can.

and enables you to go places that in times passed would not have been tackled.

But GPS never says you should.
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Old 20-12-2010, 12:33   #4
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Context is everything. Knowing where the rocks are when your on the water is useful but when you're in sight of land a chart and sighting compass can go a long way to helping with that.

I've hiked a lot in heavily wooded mountains. If you stay in the watershed you started in it's usually pretty easy to find your way back to something familiar but if you cross watersheds it gets more difficult and a compass can be petty useful. I've never carried GPS hiking.

Knowing landmarks is useful when sailing or hiking. Day sailing I don't bring my chartplotter (laptop based) or turn the GPS on. If I'm not sure of the hazards in an area I can use sightings on landmarks I know and a chart to tell me where I am.

I've arrived and anchored in a strange anchorage in the dark and was grateful for the chart plotter. I had counted on an closer anchorage that turned out to be very full and so soldiered on but wished I'd made the decision to stop at earlier anchorages.
“We are the universe contemplating itself” - Carl Sagan

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Old 20-12-2010, 13:04   #5
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Interesting observations, a bit philosophical.

It would be best if everyone started their sea navigation with only charts, a hand bearing compass, dividers and scale. I did and I am a better GPS/chartplotter navigator for it.

I really liked the line: GPS tells you that you can, but not that you should. Only experience can teach the should.

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Old 20-12-2010, 13:41   #6
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Overall I think Chartplotters are wonderful but they do create a couple problems
  • People leave very little clearance for map or GPS error. They will sail much closer to underwater obstructions than I believe is often prudent.
  • People spend very little time actually navigating consequently they don’t even see the information presented on the chartplotter.
For example one of my favorite anchorages Paxos in Greece has a spot shown as 1.8m deep on the chart. Its in the pilot book on all the official charts and all the electronic charts I have seen. ( I don’t think it exists the area is really about 2.4m deep).I have seen numerous boats with drafts well over 1.8m sail over this patch. If they looked at their chartplotter it would show them (incorrectly) that they were about to run aground. Very few seem to notice the information even though its presented in the clearest possible way.
I suspect without a chartplotter they would spend more time navigating including planning the passage and be more aware of these hazards.

The answer is easy use a chartplotter, but navigate with a bit more care and margin for error.

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