GPS VS LORAN

[gss036]

I am using a new Garmin 176C and a 13-14 yr old Impulse 3100(?) loran/depth sounder combo. I am using the same waypoints, yet when comparing the two on runs my GPS always shows about 1.25 miles more on a 9-10 mile leg and also a little difference in degree of heading. I sent the Garmin in for warranty repairs and got the familiar fix, corrupted software. They both get me to the same location. I think the Loran is more accurate because I have a hard time getting WAAS signals this far up in the northwest.<br />Any ideas as to why this is happening would be appreciated.

 

[Boatist]

Re: GPS VS LORAN

Gary<br />I also have both Loran C and a GPS on my boat and still use the Loran C most of the time. The Loran C is very accurate at returning to the same place, however the GPS even with out WAAS should still be more accurate. Is one unit set to Nautical Miles and the other set to Statute Miles? If going to a new point the GPS should be much better if you recieve at least 4 birds. Loran C can be off as much as 1/4 mile when finding a new location but down to about 50 feet when returning to the same location. GPS with out WAAS down to about 30 feet and with WAAS about 10 feet. At your location I and not sure you can see the AOR (atlantic ocean region) WAAS bird but should be able to see the POR (pacific) WAAS Bird. WE get both down here but even then my Garmin GPS usually say about 15 feet accuracy.<br /><br />I still use my Loran C because I have so many more waypoints put into it, The GPS always shows a slightly different positoin than the Loran C reports. Still Both are more than good enough for Us.

 

[gss036]

Re: GPS VS LORAN

They are both set for Statute miles and magnetic reading so the compass reads the same. I really get close reading from the compass and Loran, but not the GPS.<br />I only get the Pacific region part-time, depending on location, too many mountains. <br />I was wondering if the error could be because of software in the Loran being so old that the magnetic difference has changed that much over 12-14 years? We do have a couple of spots here that has warning on the charts for magnetic compass error.

 

[Boatist]

Re: GPS VS LORAN

Yes the mountains will do it as POR is low on your horzison as it has to be on equator.<br />I thought you were out on the open ocean. Even here at 38 degrees north in the mountains it is hard to get WAAS signal. Over 12 years the the compas heading would have decreased 1 degree. 5' per year.

 

[mattttt25]

Re: GPS VS LORAN

i could be way off, but i'm almost certain loran and gps coordinates are not the same. i seem to remember having to convert when going from one to the other. maybe it was something to do with a different datum? it's been a few years since i was up on the bridge...

 

[Boatist]

Re: GPS VS LORAN

Matt<br />Many LORAN C used TD (Time Delay or Time Difference) readings and some charts had those TD lines on them. My Loran C can run in TD's or Latitude and longitude. GPS will use Latitude and Longitude but units like my Garmin will convert from TD's. <br /><br />The GPS units has one extra digit.<br /> GPS Loran C<br /> 38 18.310' N 38 18.31' N<br />123 02.962'W 123 02.96'W<br /><br />The Loran C is not as accurate at finding an actual Lat and LONG location, but once you have marked the location still very good at going back to same location. GPS will be more accurate at finding the location the first time with the LAT and LONG location.<br /><br />Likely will be a small difference bettween the Latitude and Longitude between GPS and Loran C but should be less than 1/4 mile. Better Loran C have ASF (addition secondary factor) correction table. This is a grid by grid correction to make closer to actual Lat and Long. Coast Guard and NOAA made these grids but did not do all areas.<br /><br />One other difference with Loran C is it is land based and covers the US but is not world wide like GPS.

 

[mattttt25]

Re: GPS VS LORAN

thanks for the refresher course boatist. i could go back and re-qual now!

 

[johndezman]

Re: GPS VS LORAN

having listened to the above, all i can add is that the channel i navigate from my marina out to lake erie has about 10 pairs of markers (channel is about 50-100 ft wide). i can gauge my location graphically on the screen of my Northstar 951. <br /><br />a fifty foot target area would definitely be noticable in that environment. i feel my accurace is arounf 10'!

 

[gss036]

Re: GPS VS LORAN

That was the reason for my concern in the magnetic differences. My loran is set is for Lot/Lat as w/GPS. I know my Loran waypoints are right on since I have personally set and run each one. We have several passes between the San Juan and Canadian Gulf Islands that we go through and they are only 25-35 feet wide. Not much room for error in the fog. I normally will not go out in the fog, but sometime the draw pulls you to go out knowing that it will clear in a couple of hours. Not like the past few days up here, socked in all day on the water. On Wed/Thur there was 2 Wa State ferries that had to go to full reverse while going forward to avoid collision in Elliot Bay in Seattle. Somebody wasn't watching the radar.<br /> I really like have the Bluewater chip on the Garmen 176C. You can look at the screen and know where you are even if you cannot see land, with the Loran you are just looking at marks on a screen, know what I mean.

 

[Boatist]

Re: GPS VS LORAN

Gary<br />My Loran C and GPS do the same as yours if I just put my saved Loran Waypoints into the GPS. However if I run the Route and follow my Loran Route and Save the waypoints to my GPS then they will both guide me thru the same channel. The saved Lat and Long will be slightly different for the same location. This is because Loran can be off as much 1/4 mile even with ASF ON and without ASF even more. If you run your channel and set waypoints between Buoys in both units then compare to the light list for bouys I think you will find the GPS to be closer to the light list location.<br /><br />I do not know if you can even buy a Loran today but later unit Lorans you could also get with a chart plotter type display. Today you can get GPS units with displays just like the old Lorans but most people prefer the Chart Plotter so that is mostly what you see today. In the dense fog Rardar is the way to go. Both GPS and Loran will tell you where you are but Rardar will also show targets around you. Makes no difference if you hit a Buoy or ship at sea, it is still a bad day.