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Old 09-02-2014, 10:23   #16
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Re: The Modern Navigation Trap

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Originally Posted by tomfl View Post
While I do wear glasses I have found looking at the things around me is a big clue to where I am.

I have also noticed that there are apps you can use (on a computer, tablet, or cell phone) that indicate the margin of error your GPS unit is currently experiencing. While most of the time it is quite small it does change, sometimes to values larger than I would expect.
Best comment on here. a chart or gps is just another tool. Take it with a grain of salt and .........USE YOUR EYES AND BRAIN!
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Old 09-02-2014, 11:27   #17
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Re: The Modern Navigation Trap

Yes ran into this years ago when we first started using GPS in the military. Found maps with differing datum and people who said they we're in the same location but 800 meters apart.
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Old 09-02-2014, 13:14   #18
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Re: The Modern Navigation Trap

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There was a snarky reply for a few minutes after your first post. I replied to it, and then the snarky post had been deleted.
Yeah, I thought why reply at all.

So I deleted it.
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Old 09-02-2014, 13:40   #19
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Re: The Modern Navigation Trap

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Yeah, I thought why reply at all.

So I deleted it.
No problema, amigo. I surely wish I had not hit "submit" a bunch of times.
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Old 09-02-2014, 14:21   #20
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Re: The Modern Navigation Trap

I wonder what kind of navigation equipment they weren't using on the USS GUARDIAN (MCM-5).

http://edition.cnn.com/2013/04/08/wo...ilippine-reef/
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Old 09-02-2014, 14:29   #21
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Re: The Modern Navigation Trap

I don't know about the military, but us regular folks don't get DGPS unless we pay a subscription fee. It is supposed to be much more accurate, we use it on Dynamic Positioning vessels when we need to keep a very tight foot print due to operations.
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Old 09-02-2014, 16:47   #22
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Re: The Modern Navigation Trap

The axiom I was taught about everything that has to do with moving from point a to point b is "Trust but Verify." Position, depth, course, fuel remaining, whether the bouy you see is really the one you think it is, whether the bilge is dry, condition of the engine room every hour, ... everything . I don't carry paper charts anymore but I have three separate plotters all with different nav programs and chart sources. They often disagree. When in skinny water or close to skinny water my wife and I are both on the bridge and agree on the next marker being what we think it is.
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Old 09-02-2014, 16:53   #23
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Re: The Modern Navigation Trap

Anybody ever use old French charts where the prime meridian ran through Paris rather than Greenwich?
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Old 09-02-2014, 17:17   #24
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Re: The Modern Navigation Trap

Mistakes on charts are quite common once you start sailing away from popular areas.

The most common is a simple displacement of the chart, but there are occasional large errors in the charted depth.

As Dockhead says a radar overlay on top of an electronic chart is the best way to detect the former type of error. An alternative is to use traditional navigational techniques such as clearance bearings or a three point fix. These techniques work even if the map is displaced. They should be used much more frequently. They can be done with paper or electronic charts.

It is very common for people to rely on the GPS fix alone. This is not enough especially in areas where the navigation is tight and you are unsure about the maps (which is any new area).

For the latter type of incorrect depth error keep a careful watch on the depth gauge. Someone at the bow is often a good idea when coming into an anchorage.
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Old 09-02-2014, 17:47   #25
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Re: The Modern Navigation Trap

Here is something I wrote several years ago on chart errors. Feedback is welcome.

===>Inland Waters Resources - Chart Errors

And a point about DGPS: There are subscription DGPS services with special equipment and/or extra ground stations, but standard DGPS is free. It does, however, require buying a special equipment, but no fees.

WAAS is the latest and has been operational in the US since about 2006. Most GPSs built since around 2004 have been WAAS capable with no extra equipment or fees. My Garmin GPS V was WAAS enabled, as has been every GPS I've had since.

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Old 10-02-2014, 00:19   #26
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Re: The Modern Navigation Trap

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This is all fairly elementary navigation, and something most sailors learned in their first (or second) navigation lesson.
Dockhead - your statement here is true. Unfortunately, there are now many sailors out there who have never taken a single navigation lesson in their life. They have boat, with a chart plotter and sail it exactly the way as they drive their car with a GPS/map in it.

I don't want to sound like a Luddite, especially since I use all the modern navigational aids there are. But sailing a boat (sails or motor) without understanding basic navigational techniques is ridiculous.

There are many of them out there though.
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Old 10-02-2014, 06:49   #27
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Re: The Modern Navigation Trap

I would never use a DP system in a confined space such as a lock, I have had them go bugshit too many times without warning.
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Old 10-02-2014, 06:59   #28
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Re: The Modern Navigation Trap

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They have boat, with a chart plotter and sail it exactly the way as they drive their car with a GPS/map in it.
Don't you just love these stories that come out in some news outlet about every few months about some dummy following his GPS who drove into a quarry, or off a bridge, or a very recent one, across the border into Canada?

With a paper chart, when you determine that a rock or jetty is in fact 10 meters east of where it's drawn, you can use this strange little tool called a #2 pencil to correct that. It's kind of like an iPad stylus, except it's made out of wood and has a solid graphite core to it. When you swipe it down a paper chart, it leaves a trace. Positions corrected on paper charts actually stay where you put them. Forever.
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Old 10-02-2014, 07:38   #29
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Re: The Modern Navigation Trap

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With a paper chart, when you determine that a rock or jetty is in fact 10 meters east of where it's drawn, you can use this strange little tool called a #2 pencil to correct that. It's kind of like an iPad stylus, except it's made out of wood and has a solid graphite core to it. When you swipe it down a paper chart, it leaves a trace. Positions corrected on paper charts actually stay where you put them. Forever.
I do exactly the same on our electronic charts. Radar overlay even makes it much more accurate and precise to do so. And I can color it, label it, etc.

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Old 10-02-2014, 07:41   #30
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Re: The Modern Navigation Trap

yeah, I got one of those radars too. Fold it up, stick it in your back pocket, sit on it, get it wet, jump in the dinghy and run around to a bunch of isolated cays and take that radar and chartplotter out of your wet cargo shorts pocket and spread it out there on the bow of the inflatable dinghy and read all those rock positions.....and you can use it to light a fire in a real survival situation.
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