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? for the GPS experts


DTro

Question

Is the accuracy of a non-WAAS unit (Magellan 315) good enough to trust on river on a foggy night? For example if I plotted a course on the way to fishing hole, could I rely on the plotting to get me back, half blind?

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I used non-Waas for many years. yes you can rely on it pretty good. Even with all the latest techhnology at night and foggy take it slow and easy.

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I think most people tend to exagerate the accuracy of their GPS units. As a guide, you might want to assume that it is accurate to about 10 feet in any direction about 95% of the time. If you are trying to follow a recorded track, you have to allow for the error in the recording and the error in the current reading, so you may want to assume that you could be 20 feet off the mark in any direction when following a track. In addition, you should allow some error for your ability to actually stay exactly on the track. If I was trying to navigate dangerous water in the dark, I would not want my track to be within 50 feet of any obstruction. And then I would still crawl along.

Lots of things can make accuracy worse, such as atmospheric conditions,obstructions such as trees, etc. Try this as an experiment: from a fixed position, such as a dock, set numerous waypoints over differnet days and times. Check to see how much of a scatter you get.

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I have a 9 year old Garmin GPS III - been doing it for years.

I've tested it many times, especially during ice fishing on snowmobile. If I want to find my old tracks in the snow, or my old holes from a week ago...it will lead me right to the spot.

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dtro -

I have used mine a few times for exactly what you want to do being us Cat men on the MN, it does help. However, you really have to play around with the settings for saving the tracks. And if you are going to save them to your PC and delete them from your unit and then re-download them to your handheld at a later date, then you might lose some parts of the track if it is real long. I had mine set a point every 15 feet.

But in general, it will work. But you still need to go slow. And also use the track back on a saved track during daylight hours before you really need to rely on it.

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I have an LMS332C, yes it has WAAS. I used it in the fog- worked great. I used it to go back one night, worked great. But I also hit a submerged stump and I was dead on my track. So If I missed the stump or rock by 3' going out, there is no guarantee that you won't hit it coming in. I feel that you might be no better than 50' one way or another. but most of the time you are better than that. But that is a whole lot better than guessing where you are.

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Hmmm... I was in the boat with dtro on previously mentioned foggy night.

I'm willing to bet that accuracy 10 feet to each side of the boat or about 15'-20' of dead-on accuracy would have been rather worthwhile that night.

Its hard to run the river at anything more than idle not knowing where the trees, stumps, branches, and snags are at in the fog.

We passed all this debris on the way downstream in the daylight, we knew where it was coming back, but also didn't want to take any chances at all. It was a slow trip.

Good job dtro. Sorry about the monkey poo on the carpet. smirk.gif

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hey musky hunter how far in were you zoomed when navigating in the fog? I try to zoom in as close as possible without "outrunning" the unit's update capacity.

Did this numerous times last week in Canada navigating a narrow and twisting river. Visually, it appeared that there was very little "slop" in my repeated passses.

dockehr

Dr. Roland E. Kehr, Jr.

Lindy Tackle

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