Trust your eyes, not the GPS - Page 3 - SailNet Community
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post #21 of 63 Old 12-30-2009 Thread Starter
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Quote:
Originally Posted by eherlihy View Post
Ideally, I like to stay in the white.
Great advise. The owner of one of the charter companies out here has the following suggestions:
  • Sail on the white stuff
  • Anchor on the blue stuff
  • Drink on the brown stuff

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post #22 of 63 Old 01-06-2010
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Great advise. The owner of one of the charter companies out here has the following suggestions:
  • Sail on the white stuff
  • Anchor on the blue stuff
  • Drink on the brown stuff
YOU DA MAN JACK!!!!

There isn't a device on this world that can measure the indifference I have for that statement.
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post #23 of 63 Old 03-09-2010
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Trust your eyes...

Just to clear up one or two slight misconceptions previously espoused in this forum, a couple of points.

Aviation GPS normally employ Differential GPS for the approaches and departures, meaning that a time difference signal is sent out locally, to correct any errors creeping into the GPS signal. This allows all the aircraft to fly the exact same corrected route, close to the airport. Additionally, aviation charts for navigation transits employ WGS 84 as their standard.

All charts use some sort of datum (meaning a starting point for all the measurements displayed). A chart is not necessarily wrong if you are anchored 100 yards off-shore and the GPS display is showing you ˝ mile inland. GPS uses WGS 84 datum, while local charts will have their own datum marked. No problem if the electronic chart is also WGS 84. Where you can run into difficulties is when the electronic chart is a different datum and then you are overlaying your GPS position based on WGS 84 positioning. Then you get positions that make no sense. Most hard copy charts have a write-up indicating the correction that must be made to mark a GPS fix on the local chart. That seems to be lacking in electronic charts, hence causing confusion. Bottom Line: the overall advice tethered on this forum is absolutely correct: Trust your eyes, not the infernal black box.
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post #24 of 63 Old 03-09-2010
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Trust

Trust your eyes, the "infernal" black box, your ears, your nose, your crew/lookouts, and the hair on the back of your neck. GPS is a great tool and has let millions of people enjoy boating safely and efficiently. The "infernal" black box is not at fault if you have your head buried in the chart plotter, blindly following the bearing to the wrong waypoint. That's operator error.

"Seaman's eye" is the term for constantly comparing what you see to what your instruments---GPS, compass, depth sounder, wind speed/direction---and your senses---visible nav aids, the wind on your face, the color of the water, the feel of the boat, etc., etc, etc,---are telling you.
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post #25 of 63 Old 03-09-2010
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Interesting thread. In the past couple of months I purchased a Garmin chartplotter for the boat and a Garmin for the car. I recently flew into San Fran in lousy weather. Navigating all those complicated freeway connections in the pouring rain I was glad I had the GPS and wasn't juggling a map.

The difference is roads don't move. Channels and sand bars do.

For that matter you can't absolutely trust your charts either. Check the dates on yours. The ocean moves things around. But like anything else, if it's used correctly a chart plotter can be a great tool.

Jim

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The sail, the play of its pulse so like our own lives: so thin and yet so full of life, so noiseless when it labors hardest, so noisy and impatient when least effective." - Henry David Thoreau
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post #26 of 63 Old 03-09-2010
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I'd point out that the electronic charts that are supplied with a given chartplotter are usually the WGS84 datum set but that does not mean that they are accurate. Just remember your location on the chartplotter screen is an electronic representation of where your boat is in a world that was created by a human cartographer, and may or may not have any real relationship with where your boat is in the real world. A GPS chartplotter is a great tool to have, but it should never be the only thing you rely to confirm your position. If you're out daysailing, coastal pilotage is still highly recommended as is using the best and most versatile navigation instrument you've got—the Mark I EYEBALL.

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post #27 of 63 Old 03-09-2010
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You are spot on Dawg.
I was traveling up the inside passage last year on a commercial fishing boat with three other guys. One was older and not an experienced boater so he was "daylight" only at the helm. As we were approaching our destination and entering a very narrow, twisting channel with so many nav aids it was difficult to figure out which way to go, the older fellow who had the helm, asked if I could plot a route on the chart program for him to follow. I explained that that would be next to impossible because of the number of turns and nav aids. I told him to just follow the markers and keep the red ones on the starboard side. He adjusted his glasses and took a long, long look at the plotter screen and then said "I don't see any red markers". At this point we were less than 100 yards from the first marker/turn, so I said "you're looking at the wrong screen" and pointed out the wheelhouse window.
The owner of the boat, who had overheard the discussion, took over the helm.

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post #28 of 63 Old 03-22-2010
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It has to be between 15-20 years since I got my first GPS, a Garmin GPS 12. I used to spend hours during the winter entering waypoints and routes by taking the lat and lon off my paper charts. I can't think of one problem that was not the result of human error (mine). I had a similar issue where the GPS was taking me across an island off the coast of Maine. I was semi-blindly following the GPS compass to the next waypoint when I happened to notice that the distance to the next marker was about 200 mi. not the 2 that it should have been. One digit in a coordinate can mage a big difference.

Chartplotters are much safer in that they tend to make user errors much more obvious. You still need to have at least two confirming sources of info. That is one reason thet I really like radar overlays on charts. It confirms land masses and aids to navigation. I turn the radar on at least once a day even perfect weather just to make sre it is working and agrees with the electronic chart and wht I am seeing.
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post #29 of 63 Old 03-22-2010
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Quote:
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The difference is roads don't move. Channels and sand bars do.
You haven't driven around Boston, have you...


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post #30 of 63 Old 03-22-2010
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Now Ed, we only do that once every couple years to torture the tourists...
Quote:
Originally Posted by eherlihy View Post
You haven't driven around Boston, have you...

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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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