We went away yesterday and anchored a little way up the Sacramento Delta. As the area where we were anchoring has some real shallow spots, I carefully watched our location on our GPS and then confirmed it with our charts. Strange thing - according to what the GPS said was our location, we were several hundred yards up on the land! This morning, after weighing anchor and getting the sails up, I put her on auto-pilot... and promptly almost jibed before I could get back to take it off auto pilot. When I checked, I saw that the GPS reading of our heading was about 40 degrees different from what the compass said. I checked with a hand-held compass and it was the same thing. Another thing I noticed: When I put it on auto pilot with the engine running, it still shows an incorrect heading, but it doesn't turn the wheel crazily as it did when under sail. We have an Autohelm 4000+. Any ideas on what's wrong, whether it can be fixed, if so how, or whether I should just get a new autopilot? Thanks. John PS. All of us, including the two dogs, had a great time.
GPS acting weird
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Double checked
As I said, I'm pretty sure it's showing the wrong heading since two different ompasses (one on the binnacle and a handheld one that I put looked through from different parts of the boat) were both showing the same reading and about 30 degrees different from the GPS reading. And I'm certain it shows the wrong location. I took a couple of bearings on the GPS and just now I checked them with the chart. In both cases, the GPS bearing was quite a bit off from where I know I was. (One was just at the entrance to our marina.) Does this mean the microprocesser is bad? If so, can it be fixed, replaced, or do I need a new GPS?
As I said, I'm pretty sure it's showing the wrong heading since two different ompasses (one on the binnacle and a handheld one that I put looked through from different parts of the boat) were both showing the same reading and about 30 degrees different from the GPS reading. And I'm certain it shows the wrong location. I took a couple of bearings on the GPS and just now I checked them with the chart. In both cases, the GPS bearing was quite a bit off from where I know I was. (One was just at the entrance to our marina.) Does this mean the microprocesser is bad? If so, can it be fixed, replaced, or do I need a new GPS?
Raymarine Q&A
John, go out to Raymarine Q & A customer service and you may find an answer. I had a failure on my 4000 and it was the head unit, It could also be the compass. Before anything else, re-initialize it according to the manual. Worked for me once. Rick D.
John, go out to Raymarine Q & A customer service and you may find an answer. I had a failure on my 4000 and it was the head unit, It could also be the compass. Before anything else, re-initialize it according to the manual. Worked for me once. Rick D.
GPS and maps
All modern maps where made before GPS. So expecting the steel tape and theodolite surveyed maps to jive with 30- meter GPS positions (especially in CA) is taking your life into your own hands. I think this is a not so well documented effect that most are not aware of. I know the maps I used in the army had this problem (+-300 meter accuracy) when using a GPS to do land navigation. With that said if you have old maps and you are in a delta with shifting channels then no GPS is going to work for you. I think this is the reason that most folks will tell you not to us GPS as the only means of navigation. IMHO GPS will do great at getting you to the vicinity of the area you are going but pilotage is still a necessary tool to get you there. I'd be interested to find out what other folks GPSs read when they go past that fixed outer marker. Does it give your known position to within the limits of the GPS you have? I know mine almost never shows me where I know I am. Actually that is misleading, my GPS is super accurate but my map is not so it would be more accurate to say my map almost never shows me where my GPS indicates I am. Something like +-100 yards is typical for me. That is even when the WAS is operating and I'm getting -30 meter accuracy. The problem is the map does not have the fixed marker located correctly and so when I plot a GPS point it shows an "error" Now if you hit "fix" as you pass the fixed marker so you can return to it later you are syncing the map and the GPS coordinates. The actual lat/long of the GPS fix will not plot out right on the map however. Try it.
All modern maps where made before GPS. So expecting the steel tape and theodolite surveyed maps to jive with 30- meter GPS positions (especially in CA) is taking your life into your own hands. I think this is a not so well documented effect that most are not aware of. I know the maps I used in the army had this problem (+-300 meter accuracy) when using a GPS to do land navigation. With that said if you have old maps and you are in a delta with shifting channels then no GPS is going to work for you. I think this is the reason that most folks will tell you not to us GPS as the only means of navigation. IMHO GPS will do great at getting you to the vicinity of the area you are going but pilotage is still a necessary tool to get you there. I'd be interested to find out what other folks GPSs read when they go past that fixed outer marker. Does it give your known position to within the limits of the GPS you have? I know mine almost never shows me where I know I am. Actually that is misleading, my GPS is super accurate but my map is not so it would be more accurate to say my map almost never shows me where my GPS indicates I am. Something like +-100 yards is typical for me. That is even when the WAS is operating and I'm getting -30 meter accuracy. The problem is the map does not have the fixed marker located correctly and so when I plot a GPS point it shows an "error" Now if you hit "fix" as you pass the fixed marker so you can return to it later you are syncing the map and the GPS coordinates. The actual lat/long of the GPS fix will not plot out right on the map however. Try it.
Check for steel.
I moved some tools less than six inches closer to the flugate sensor on our 4000+ and it went nuts. Moved them away and problem solved. Ours is not hooked up to a GPS yet, so that may not be all of the problem.
I moved some tools less than six inches closer to the flugate sensor on our 4000+ and it went nuts. Moved them away and problem solved. Ours is not hooked up to a GPS yet, so that may not be all of the problem.
I think it's something else
I read an article over the weekend (either in Cruising World or Sailing) about a new GPS satellite that may not be working with older GPS units. The Coast Guard (or some other organization) wanted to hear about it if people were experiencing problems with it.
I read an article over the weekend (either in Cruising World or Sailing) about a new GPS satellite that may not be working with older GPS units. The Coast Guard (or some other organization) wanted to hear about it if people were experiencing problems with it.
May be two problems
GPS positional error can be a result of datum conflict. IE: You may have a datum setting in your GPS which is different from your chart datum. It is a setting on many units which can be changed by the user. Check that setting and then look at the chart and see if they are the same. It probably should be WGS84. Heading error may be from the autopilot fluxgate sensor being miscalibrated or there may be something magnetic or ferrous near to it physically. Read your manual to recalibrate it and or check for a nearby tool box or something magnetic near to it.
GPS positional error can be a result of datum conflict. IE: You may have a datum setting in your GPS which is different from your chart datum. It is a setting on many units which can be changed by the user. Check that setting and then look at the chart and see if they are the same. It probably should be WGS84. Heading error may be from the autopilot fluxgate sensor being miscalibrated or there may be something magnetic or ferrous near to it physically. Read your manual to recalibrate it and or check for a nearby tool box or something magnetic near to it.
GPS problem
Went out Sunday and my Garman Map76 would not acquire satellites and date and time were incorrect. I read about the new satellite in Sail and it may cause problems as Stan mentioned. I changes batteries and it wan not any better. Has anyone else had this problem?
Went out Sunday and my Garman Map76 would not acquire satellites and date and time were incorrect. I read about the new satellite in Sail and it may cause problems as Stan mentioned. I changes batteries and it wan not any better. Has anyone else had this problem?
Garmin
I had a similar problem with my map76. While it's sometimes hard to tell exact positon on open water, while sailing in a familiar lake last year I marked several waypoints just for fun withone of them dead center in a channel leading to a different section of the same lake. the following week ALL of them seemed to be a few hundred yards off.
I had a similar problem with my map76. While it's sometimes hard to tell exact positon on open water, while sailing in a familiar lake last year I marked several waypoints just for fun withone of them dead center in a channel leading to a different section of the same lake. the following week ALL of them seemed to be a few hundred yards off.
A few years ago the CG issued a notice to mariners.
They warned of erratic GPS readings caused by land-based interference. I forget the details. The warning came out about the time we launched after the rebuild. Sure enough, in our cozy berth, the GPS showed that we were bouncing all over the marina. And it even happens in the wilds of Canada. Never trust electronics except radar.
They warned of erratic GPS readings caused by land-based interference. I forget the details. The warning came out about the time we launched after the rebuild. Sure enough, in our cozy berth, the GPS showed that we were bouncing all over the marina. And it even happens in the wilds of Canada. Never trust electronics except radar.
Chart Datum (if anyone is still reading this thread)
The first thing you must do is verify the 'Datum' that the chart is drawn to, then select that 'Datum' in the GPS setup. WGS84 is 'World Geodetic System' revised in 1984, but most charts were drawn to different systems such as NAD27, or NAD83 (North American Datum). Some GPS's have an actual 'compass', but most do not. The compass that you see in the GPS can only work if you (the GPS) are moving. It will then indicate your course over the earth in either 'True', or 'Magnetic' (depending on your settings) direction. The lat/lon readings may not agree with the chart unless the datum of the chart is selected in the GPS.
The first thing you must do is verify the 'Datum' that the chart is drawn to, then select that 'Datum' in the GPS setup. WGS84 is 'World Geodetic System' revised in 1984, but most charts were drawn to different systems such as NAD27, or NAD83 (North American Datum). Some GPS's have an actual 'compass', but most do not. The compass that you see in the GPS can only work if you (the GPS) are moving. It will then indicate your course over the earth in either 'True', or 'Magnetic' (depending on your settings) direction. The lat/lon readings may not agree with the chart unless the datum of the chart is selected in the GPS.
yesterday
I was out at our boat yesterday and checked the gps. This time, sitting at the dock, it showed the same heading as the magnetic compass (within a couple of degrees). This is what it had done in the past. Then I made a mistake. I took out the manual and started fooling with the gps. I went to trip computer and erased the previous data. No problem with that. But after that, the gps map was acting weird. It shows land and the bay, but not the Alameda estuary. This was so no matter how much I zoomed in or out. According to the gps map, the boat was sitting on dry land. Before I started messing with it, it was showing the estuary just fine. In fact, it was showing exactly where the boat was in the marina.
I was out at our boat yesterday and checked the gps. This time, sitting at the dock, it showed the same heading as the magnetic compass (within a couple of degrees). This is what it had done in the past. Then I made a mistake. I took out the manual and started fooling with the gps. I went to trip computer and erased the previous data. No problem with that. But after that, the gps map was acting weird. It shows land and the bay, but not the Alameda estuary. This was so no matter how much I zoomed in or out. According to the gps map, the boat was sitting on dry land. Before I started messing with it, it was showing the estuary just fine. In fact, it was showing exactly where the boat was in the marina.
Removing data
If you have previously loaded charts, the basic marine information loaded on the GPS when you bought it may have been over written. On my Garmin MAP76, I loaded the charts, later I removed them and all preloaded information was gone. You can download the factory information from their web site. I do not know if this is the problem or if you have a Garmin. Has anyone tried the Garmin web site to see if there is a fix or if they are aware of any of these problems? Most on this thread seem to have a location and speed problem, my problem is satillite acqusition, time and date.
If you have previously loaded charts, the basic marine information loaded on the GPS when you bought it may have been over written. On my Garmin MAP76, I loaded the charts, later I removed them and all preloaded information was gone. You can download the factory information from their web site. I do not know if this is the problem or if you have a Garmin. Has anyone tried the Garmin web site to see if there is a fix or if they are aware of any of these problems? Most on this thread seem to have a location and speed problem, my problem is satillite acqusition, time and date.
Expectations and Prudent Seamanship
John, My friend and fellow shipmate, David, has a 76, too, and we use it onboard, along with our old Magellan Blazer 12. I think you may need to reconsider your expectations about what a GPS is intended to do, especially one without mapping characteristics, like your Garmin 76. The instruction manual, which I have downloaded to my computer since I needed to learn how to use it because of its presence onboard, says: "It is the user's responsibility to use this product prudently. This product is intended to be used only as a travel aid and must not be used FOR ANY PURPOSE REQUIRING PRECISE MEASUREMENT OF DIRECTION, DISTANCE, LOCATION OR TOPOGRAPHY." Almost every single known text or manual about navigation says not to rely solely on ONE instrument. What they neglect to also tell you is not to get too consumed in trying to get everything on your boat to agree with what every other instrument is telling you. That's why YOU are there, to make sense out of conflicting information. BTW, they teach that in Navy navigation courses, too. The ONLY way I know to do that is to practice, practice, practice, and then learn to judge what you're seeing. A perfect example is radar. If you don't learn to use it during nice weather and in daytime, no way are you going to be able to use it when it's needed. I know you said you were heading for China Camp, which is nowhere near the Sacramento Delta, so where were you when this happened? Your "heading" information issue is another perfect example. On our boat I have made note that the headings are sometimes [repeat: sometimes] different between our Ritchie compass and the Autohelm compass readout. Some of that could be due to currents affecting boat heading vs COG. The reason is simple: use this example - you're heading down a river; the current is so strong it skews your boat sideways, 90 degrees to the downstream direction of the river; your GPS will be 90 out from your compass because you're going sideways, the boat's bow is pointed at the bank and the boat is going downriver. I recommend you do some more real world testing of your instrumentation before you give up the ghost. As also earlier suggested, recalibrating your autopilot would be a good (first) step for that part of your equipment. Also, as suggested, check the Garmin website for software updates for your GPS.
John, My friend and fellow shipmate, David, has a 76, too, and we use it onboard, along with our old Magellan Blazer 12. I think you may need to reconsider your expectations about what a GPS is intended to do, especially one without mapping characteristics, like your Garmin 76. The instruction manual, which I have downloaded to my computer since I needed to learn how to use it because of its presence onboard, says: "It is the user's responsibility to use this product prudently. This product is intended to be used only as a travel aid and must not be used FOR ANY PURPOSE REQUIRING PRECISE MEASUREMENT OF DIRECTION, DISTANCE, LOCATION OR TOPOGRAPHY." Almost every single known text or manual about navigation says not to rely solely on ONE instrument. What they neglect to also tell you is not to get too consumed in trying to get everything on your boat to agree with what every other instrument is telling you. That's why YOU are there, to make sense out of conflicting information. BTW, they teach that in Navy navigation courses, too. The ONLY way I know to do that is to practice, practice, practice, and then learn to judge what you're seeing. A perfect example is radar. If you don't learn to use it during nice weather and in daytime, no way are you going to be able to use it when it's needed. I know you said you were heading for China Camp, which is nowhere near the Sacramento Delta, so where were you when this happened? Your "heading" information issue is another perfect example. On our boat I have made note that the headings are sometimes [repeat: sometimes] different between our Ritchie compass and the Autohelm compass readout. Some of that could be due to currents affecting boat heading vs COG. The reason is simple: use this example - you're heading down a river; the current is so strong it skews your boat sideways, 90 degrees to the downstream direction of the river; your GPS will be 90 out from your compass because you're going sideways, the boat's bow is pointed at the bank and the boat is going downriver. I recommend you do some more real world testing of your instrumentation before you give up the ghost. As also earlier suggested, recalibrating your autopilot would be a good (first) step for that part of your equipment. Also, as suggested, check the Garmin website for software updates for your GPS.
thanks
Stu, Thanks for all the suggestions. However, as I commented before, the difference between both compasses (a binnacle-mounted one and a hand-held one) was about 25-30 degrees on all different headings as well as when she was sitting in her berth. This included carrying the hand-held compass to different parts of the boat. Plus, when I put it on auto-pilot it turned the wheel wildly. A day or two later, though, I checked and the gps was showing the same as the compass, within a few degrees. I have no idea what happened. I haven't tested the auto-pilot yet to see if that's working now. Now, if I can just get the information back - showing the estuary - then I'm back to square-one - which is minimally using the gps (as I still don't really know how to use all its different functions). John
Stu, Thanks for all the suggestions. However, as I commented before, the difference between both compasses (a binnacle-mounted one and a hand-held one) was about 25-30 degrees on all different headings as well as when she was sitting in her berth. This included carrying the hand-held compass to different parts of the boat. Plus, when I put it on auto-pilot it turned the wheel wildly. A day or two later, though, I checked and the gps was showing the same as the compass, within a few degrees. I have no idea what happened. I haven't tested the auto-pilot yet to see if that's working now. Now, if I can just get the information back - showing the estuary - then I'm back to square-one - which is minimally using the gps (as I still don't really know how to use all its different functions). John
John, the compass on the GPS will not work unless you are
moving. MaineSail mentioned that in an earlier post. I daresay it is also covered in the Garmin 76 manual, see page 17. Are you out of "simulator" mode? English is an imperfect language, and I'm trying to understand what compasses do not agree. You seem to have four: handheld, binnacle, GPS and autopilot (assuming your autopilot has a digital course heading readout). So please help me to understand which two don't agree, because I don't understand your reply #20 as written. FWIW, I have found that particular model extremely difficult to use and counterintuitive. Stay with it, you may have to write your own mini-instructions step by step, I did.
moving. MaineSail mentioned that in an earlier post. I daresay it is also covered in the Garmin 76 manual, see page 17. Are you out of "simulator" mode? English is an imperfect language, and I'm trying to understand what compasses do not agree. You seem to have four: handheld, binnacle, GPS and autopilot (assuming your autopilot has a digital course heading readout). So please help me to understand which two don't agree, because I don't understand your reply #20 as written. FWIW, I have found that particular model extremely difficult to use and counterintuitive. Stay with it, you may have to write your own mini-instructions step by step, I did.
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