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Trust your eyes, not the GPS

11K views 62 replies 35 participants last post by  AE28 
#1 ·
#3 · (Edited)
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.
 
#5 ·
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
 
#6 ·
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.
 
#7 ·
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!
 
#8 ·
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)
 
#9 ·
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....
 
#15 · (Edited)
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....
Seeing that "MAPS" are for land, such as roads, political enities, (towns, counties, etc.) and so forth. Such as what highway to take from your town to the next.

I prefer CHARTS for Water ways and coastal transits. Charts are for Navigators who want to know the channels, depths of waters and Navigational Aids, Navigational hazards and so forth...

I have my students bring in donuts everytime they make this mistake... Yah! I've put on weight.

Do you see the difference? :hothead
Do you understand the difference?:hothead
GPS is a good tool. But you should never rely 100% on it. Practice your Coast piloting, your celestrial (sextant required) and plot your course on a paper chart if you have them. With Guests on board or the Kids get them involved in Navigation. You will learn more and become comfortable in your skills while teaching others a new skill.
 
#10 ·
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....
 
#11 · (Edited)
GPS is great for getting a position fix, an electronic version of celestial, it gives very accurate fixes.

Charts (datum, projections, updating, accounting for errors, etc), using fixed lights and light lists, sounds and sound signaling (horns, etc), compasses (and correction), dead reckoning, piloting (soundings, turning, logs, bearings), reading shoals and banks, fog, tides, currents, radar (reflection, refraction, ranging, echos), route planning, celestial (sights, reduction, time keeping, sextant use and maintenance), sailings, keeping watches, voyage plans, ocean state (waves, currents, ice), weather (reports, forecasting, routing, etc), weather monitoring (pressure, humidity, etc), etc, ... all that pesky stuff that goes under the heading "navigation", all of that stuff remains relatively unaffected by the fact that we can get a very accurate fix from a GPS receiver. In fact, Bowditch, the 800+ page "The American Practical Navigator" devotes precious (even worrisome) few pages to using GPS to get a very accurate fix. Said another way, knowing where you are at has very little to do with whether you are about to be run over by a freighter in the fog, or be swept on to a lee shore because the wind is clocking ...
 
#12 ·
This is outrageous. I spend hard currency on these devices to relieve my of the burden and responsibility of thinking for myself. Now I find out that they aren't 100% accurate, 100% of the time and they don't even warn me when I'm about to do something stupid?

I demand a refund and an apology.
 
#13 ·
In another published report about the couple stuck off-road in Oregon, a law enforcement officer was quoted as saying their GPS was set up to show the shortest route.

I have almost no experience with GPS on the water but use one quite a bit for routing on land.

I still haven't read a report of their GPS malfunctioning, so I'll continue thinking the couple screwed up.

Paul
 
#16 · (Edited)
GPS has resulted in significant safety improvements in aviation where it's used in highly complicated and risky situations such as commercial airliners shooting instrument approaches in near zero visibility at congested airports.

How is this possible given the issues we're seeing with GPS usage for marine and land navigation? A couple critical differences:
1. Aviation GPS maps are specifically maintained and certified for navigation use
2. Pilots are legally required to have current map information loaded into their GPS units if they are being used for navigation
3. GPS equipment must be certified for specific uses (e.g., instrument approaches, enroute, Visual Flight Rules only)
4. Pilots working in poor weather conditions have significant other ground based support (i.e., control tower vectoring, radar services, etc.)

Until maine GPS units and maps are certified for specific marine navigational uses, they should only be thought of as helpful backups. We know they can help us stay out of trouble, but they can also get us into it if we trust them beyond their limitations.

The current situation where a combination of up to date and out of date (and sometimes very out of date) map information has now been converted into electronic form and loaded into GPS units that are highly accurate w.r.t. your position, creates a false sense of security for users that are not fully aware of the limitations.

I feel there's so much reliance now on GPS for marine use that there needs to be a more concerted effort to correct out of date mapping information, and also to make it more obvious to users when the maps they are using are presenting information that has not been recently verified. The maps may show when depth soundings were taken for example, but often times this doesn't get displayed clearly, and/or users are not paying any attention to the significance of this information.

It seems we need a better process for providing feedback to the map information source providers (e.g., US gvmt) when errors are found, and for them to be able to update and diseminate the information quicker. Maybe industry GPS leaders such as Garmin should be doing more to lobby for this. How can we get them to do that? Hold them at least partially accountable when information from their devices assists us in getting into trouble? Yes, as captains, we're ultimately responsible for our own navigation, but we also need to do something to presure suppliers to give us better quality information. They're making money on this after all.

As a manager once told me, "you deserve what you tolerate". Should we stop tolerating out of date and unverified mapping information being given to us and respectfully demand an improvement to the status quo?
 
#19 · (Edited)
I feel there's so much reliance now on GPS for marine use that there needs to be a more concerted effort to correct out of date mapping information, and also to make it more obvious to users when the maps they are using are presenting information that has not been recently verified. The maps may show when depth soundings were taken for example, but often times this doesn't get displayed clearly, and/or users are not paying any attention to the significance of this information.
My vote is that they put all the chart information into categories, and the worst categories of charts can only be displayed on GPS units as children's crayon drawings. :D That would let people know that they should use the information with a little more caution than what we hope will someday be certified charts.

MC1 is right, part of the reason for the problem is that those computer vectored edges are so crisp and clear, they just must be right! People don't even think about the datum, when they were updated, etc.
 
#17 ·
MC1 reminded me of another issue with vector charts in chartplotters. They may not scan the data from the original sources correctly. Just south of Victoria BC harbour is a military exercise area WK, whiskey kilo. On at least one chartplotter that I have used, it shows as a "wreck."

I have not looked closely to see what other discrepancies exist.
 
#18 · (Edited)
GPS is an AID, not a Navigator

My wife bought a new car this past summer. It came with XM radio, and a fancy DVD/NAV package built in to the dash. The other day I tried the DVD player for the first time and found that it doesn't work with the engine running :confused:. What a POS - I would understand if it shutoff in D or R; but engine on = no DVD, engine off = no heat/AC:mad:!

Anyhoo, we've used the GPS many times to bring us hither and yon, and I like to have the map displayed to add to my situational awareness. The same day mentioned above we headed over to my brother-in-law's house (I was trying the DVD while waiting for the admiral to come out of the house - per usual:rolleyes: ) and the GPS showed us CONSISTENTLY about 1/2 mile off the road (to the south) but paralleling it. It was a cloudy day, but the GPS indicated that it had a strong fix on more than 4 satellites. I tried everything, short of shutting off the car, that I could think of to re-boot the unit, hoping that it would correct the problem, to no avail.

I'm glad that I wasn't using this unit to navigate an unfamiliar channel!

GPS is an AID to; and not a substitute for, good navigational skills!
 
#20 ·
I took a week long cruise with a friend this past summer. He and I own the same portable GPS/Chartplotter unit (Garmin GPSmap478). I showed him how I use the unit, which varies from his former technique. I believe that he now uses it as I do. Assuming that you're interested, here is what I do:

First, I get a chart and figure out where I'm heading for the day. I mark the start point, the end point, and figure out a way of getting from one to the other without crossing rocks, ATON, or the yellow and green parts of the chart. Ideally, I like to stay in the white.

Once the plan is complete, I start out. I use the GPS to confirm where I think I am as I head out of the harbor. Once outside the harbor, I use the rocker switch to point to a random spot, where I think that I may have to do something (like change heading, look for a buoy, enter a harbor, etc.) along my intended path (already marked on the chart) on the chartplotter. In effect, as I move the cursor ahead of my current position on the chart I am verifying that the chartplotter matches my chart (and I haven't missed anything). I then navigate to the random point, using the chartplotter as an aid. Once I arrive at the random point, I repeat the process to another random point along my path.

I do NOT enter a detailed series of waypoints to bring me from start to finish and use the navigate route feature to guide me through them. I believe that this: a- takes too long given the input medium (rocker switches), b- if I missed an obstruction between waypoint x and waypoint y, I'm in trouble, and I won't know it until it is too late.
 
#21 ·
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
 
#23 ·
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 ½ 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.
 
#24 ·
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.
 
#25 ·
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
 
#29 ·
#26 ·
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.
 
#27 ·
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.:eek:
The owner of the boat, who had overheard the discussion, took over the helm.
 
#28 ·
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.
 
#35 ·
This post reminds me of the incident a while back (I believe in the early days of the war in Afghanistan) when the military called in an air strike and incorrectly gave their own GPS coordinates instead of the target's coordinates. Technology doesn't necessarily take human error out of the equation, and over reliance on it and/or complacency can sometimes bring disastrous results.

Excellent idea to use the radar overlay along with a real-world visual confirmation - I hadn't thought of using it for that purpose.
 
#34 ·
Thanks Bill...

I try emphasizing this to every person I've helped install a chartplotter for....only about 1/3 really get it...
 
#39 · (Edited)
I would second the idea of using at least two sources of navigation information whenever possible. A single unconfirmed source is generally the easiest way to get into trouble.

Of course, some sailors don't have the common sense to do this and are going to be dumb enough to blindly believe a GPS chartplotter actually represents where they are in the world.

Radar, sight bearings, depth soundings, GPS, dead reckoning, coastal pilotage are all skills that NEED to be used when in sight of land. The navigation precision you need increases as your distance to land decreases. Being off by a mile or two when you're 200 miles from land is usually not a deal breaker... being off by 200' when entering a 100' wide bridge opening is... While the gross distance you're off by is less, the scale of error is much greater.... one is 1-2%, the other is 200%. :D

This is one reason I don't buy the GPS is better than Celestial Navigation... most of the time when you're using CN, you're hundreds of miles from land, and the precision of a WAAS GPS fix, while nice to have, is completely unnecessary. As you get closer to land, the duration of time between taking fixes should decrease. Offshore, taking a fix twice or four times a day is probably sufficient. Within VHF range of land, taking a fix every hour is probably sufficient. Navigating into a harbor, you damn well better be aware of your position the whole time.

BTW, for the Chesapeake sailors, I found this on another forum:

UPPER POTOMAC RIVER - GPS NAVIGATIONAL SIGNAL TESTING
THE GPS NAVIGATION SIGNAL MAY BE UNRELIABLE FROM (10 July 2009 - 10 July 2010 0000Z - 1200Z) IN THE UPPER POTOMAC RIVER DUE TO TESTING ON GPS FREQUENCIES USED IN SHIPBOARD NAVIGATION AND HANDHELD SYSTEMS. GPS SYSTEMS THAT RELY ON GPS, SUCH AS E-
911, AIS AND DSC, MAY BE AFFECTED WITHIN A 10 NM RADIUS OF POSITION (38 49.74N 077 01.55W). DURING THIS PERIOD GPS USERS ARE ENCOURAGED TO REPORT ANY GPS SERVICE OUTAGES THAT THEY MAY EXPERIENCE DURING THIS TESTING VIA THE NAVIGATION INFORMATION SERVICE (NIS) BY CALLING (703)313-5900 OR BY USING THE NAVCEN'S WEB SITE'S GPS REPORT A PROBLEM WORKSHEET AT U.S. Coast Guard Navigation Center.

CHESAPEAKE BAY - PATUXENT RIVER - GPS NAVIGATIONAL SIGNAL TESTING
THE GPS NAVIGATION SIGNALS MAY BE UNRELIABLE FROM 22 DEC 09 - 30 APR 10, 1300Z - 2300Z DUE TO TESTING ON GPS FREQUENCIES USED IN SHIPBOARD NAVIGATION AND HANDHELD SYSTEMS. GPS SYSTEMS THAT RELY ON GPS, SUCH AS E-911, AIS AND DSC, MAY BE AFFECTED WITHIN A 15 NM RADIUS OF POSITION 38-15.7N, 076-26.03W. DURING THIS PERIOD GPS USERS ARE ENCOURAGED TO REPORT ANY GPS SERVICE OUTAGES THAT THEY MAY EXPERIENCE DURING THIS TESTING VIA THE NAVIGATION INFORMATION SERVICE (NIS) BY CALLING (703)313-5900 OR BY USING THE NAVCEN'S WEB SITE'S GPS REPORT A PROBLEM WORKSHEET AT U.S. Coast Guard Navigation Center
 
#41 · (Edited)
I fully agree with Dog's comment about not blindly believing that the GPS will be correct. I think you need to assume the possibility of an error, although I think human errors or map correlation errors are more likely than system errors.

I don't agree at all with the logic behind the assertion that GPS is not better than Celestial Navigation. Sorry for the double negative. It's like saying a local undefeated golden gloves boxer who wins every bout by knockout is better than the national heavyweight champ who wins all his bouts by decision. Maybe on a relative basis but put them in the same ring and it is no contest for CN at any range against the GPS. Plus CN can't fight at night or when its cloudy, or if seas are too rough. GPS - any time anywhere. I'm still waiting for the first time that I can't get a fix or get a really bad position on the water but I AM on the lookout for it.
 
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