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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #1  
Old 12-30-2009
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Trust your eyes, not the GPS

I just saw this on one of our national news channels. I think it applies to boating as well.

CTV News | Couple stranded after GPS sends them down backwoods
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  #2  
Old 12-30-2009
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  #3  
Old 12-30-2009
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Both of the incidences cited in the story happened in my neighborhood on roads that I have traveled countless times. While I'm not sure of the exact details of the recent one, I would imagine that the couple turned left prematurely (by a hundred yards or so) onto a USFS service road. It is well marked as not being a thru road. Or they relied on directions from their GPS that routed them over a road that is simply not maintained in the winter. In the highly publicized case in 2006, the Kim family passed several signs warning that the road they were on was not open to winter traffic. Apparently believing the directions of their GPS navigation system more than the signs, they continued on, until they were stuck in the snow, 25 or 30 miles from civilization. In subsequent years, truck dispatchers have sent highway trucks over the same road in the winter, also relying on GPS directions. And it would be unwise and illegal to route commercial trucks over the one lane road any time of the year. So far the only consequence of those debacles have been expensive towing bills when the trucks got stuck ..... Oh, and the fire damage one of the dimwits caused by spinning his wheels til his tires caught fire. Anyway, Jack, you are absolutely correct. People are putting far too much faith in technology (GPS in this case) and not paying enough attention to what their eyes and ears are telling them. The GPS navigation system on a boat or in a car is not a substitute for planning your route. It is a tool that should be used along with other tools and your senses to help you make sure you are where you planned to be.
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Last edited by Izzy1414; 12-30-2009 at 03:48 AM.
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Old 12-30-2009
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Mine always takes me down one way streets the wrong way.
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Old 12-30-2009
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The following photo shows an image of my GPS screen and the track of my vessel while at anchor earlier this year.



The small loop at the upper left was my track when entering the area; the scramble around the boat icon was the track laid at anchor and the upper line to the right of the screen was laid at my departure. My anchor alarm was activated by a false reading when, within one second, my position was recorded at the acute angle to the right of the screen and again at a distant point off the screen where the two tracks at the lower left would meet. These anomalies are more likely to occur when a vessel is not underway, but it does happen. On another GPS several years earlier I had a momentary reading that my speed was over 60 knots! These are very brief incorrect data points, but they do occur. The real world always trumps your electronic image! 'take care and joy, aythya crew
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Old 12-30-2009
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It is well known that there are places where your GPS will show you sailing inland or where it may direct you over a reef. In these cases, the background map source data was bad. Some of the background maps were drawn by British seaman using a sextant over a hundred years ago. Garbage in - garbage out.

I have refused to own a GPS for inland driving. I always prefer maps. If I want the feel of a GPS, I read the map through a soda straw.

I can't imagine being so incompetant with a piece of paper that you would throw all trust to a GPS. I was always suspicious but confirmed when a friend brought on along on a trip to Canada to fish. The first clue was that it didn't recognize rout 550 from Marquette west bound to Big Bay. It said we were driving for 20 miles in forest with no roads. The back roads through Canada were a real hoot.
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Old 12-30-2009
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This reminds me of Mapquest's directions to my parents' house. Instead of going down the one road that goes all the way from town almost to their front door, it tells you to turn off about a mile before you get there, then routes you through a neighborhood, down a "road" that doesn't exist (there's a trail through the woods there, but it's gated), and then loops back out through another side road to get back on track. Ta da!
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  #8  
Old 12-30-2009
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I got a new Garmin chart plotter for my big trip last year.

I found the charts to be very accurate and made it home without incident.

Except: while going through some meandering channels behind Shawanaga Island, heading to Pointe Au Baril, I was conscientiously watching the screen on my plotter. There was a convenient mauve line heading off my bow, showing me the direction I was to travel. I made sure that I stayed on that line as the GPS knew which way I needed to go.

My wife piped up and asked where the channel was, as we were heading for some rocks and a small island.

Without looking away from the screen I said we were on course and there should be no island in front of us.

My wife insisted that there was indeed a non-watery obstruction in our path.

Why can't she just trust the technology?

I rolled my eyes and looked up - just to appease her of course, as I knew that I would see nothing but open water ahead: my GPS told me so!

Anyway, sure enough we were heading towards some keel-rending rocks and what looked exactly like an island.

I couldn't see any markers where I expected them to be - where my trusty GPS indicated they should be.

I looked off to starboard and saw something distinctly marker-like, about 100 yards away. 'Why the hell did they move the markers without updating the charts?'

I swung over, avoiding the rocks, and got back onto the channel.

I looked at my GPS and saw that the mauve line was still pointing off my bow in roughly the same direction as the channel.

It then dawned on me: the line was indicating the bearing to my next waypoint - it wasn't making accommodations for land etc. Had I followed the machine blindly our trip would have been cut very short (as would my keel!)

Lessons learned: RTFM; use the technology to assist, but rely on biology i.e. eyes, ears etc.; listen to the admiral.

Just as a footnote, upon arriving home after a two-week cruise around Georgian Bay I found a lovely letter from Garmin. The gist of the letter was that there was a recall of all of their electronic charts as they were off by a few feet. (when I contacted them Garmin informed me that my charts weren't affected by the recall)
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  #9  
Old 12-30-2009
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This thread reminds me of a recent thread froma husband/wife team navigating into a new channel/port with the wife at the wheel and the husband down below calling out directions by looking at the chart plotter...

While chart plotters are a very nice navigation assistant, in close waters they do not replace two pair of eyes, one at the helm, one on the bow watching the water for obstructions.

I personally rely more on accurate maps, and use GPS primarily to help me with location of the boat, rather than navigation per se, except in deep water over long stretches. I have seen several unhappy boaters who thought GPS was a good alternative to eyesight in fog and paid for their mistake. Rarely would I use the GPS when going up a river or into a narrow channel. That is what all the channel markers are for, and even the best GPS maps don't account for local variation.

A good sailor uses all available tools for navigation aids - this ALWAYS includes eyes and maps, usually includes GPS, sometimes radar. The more accurate and up to date the input, the more sure the course....
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  #10  
Old 12-30-2009
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Sailing Mexico's Gold coast last winter, the Raymarine plotter showed us a mile or more inland each time we anchored for the night. They've simply digitized the official Mexican charts.. and they are off by quite a bit.

Sure wouldn't consider making a landfall in the dark based solely on the plotter information....
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