Thread: Lowrance GPS Question?

Nothing is going to show you moving at .07MPH. Maybe you meant .7MPH?

The problem with any GPS indicating location at that kind of speed is that you are moving far less than the GPS error between updates. .7MPH is about a foot a second, and consumer GPS isn't accurate enough to even tell which direction you moved.

The GPS error can easily change by a quarter foot per second, even with WAAS and good satellite views, and can be much worse than that in poor reception conditions. That means the GPS is telling your chart that you are moving around in random directions all the time, and the chart display algorithm has to ignore those small movements in order to keep the cursor from dancing around rapidly.

There are some processing tricks that can let the chart track steady movement, but if you make a sudden change with the TM, your position could be way off for a short time. In order to really solve the issue, an inertial measurement system needs to be included in the hardware so the chart would find out where it was from the GPS, and then constantly get feedback on which way it is moving from the IMS. They are coming down in price and size, so you will see it someday.

The old 2000/3000 antennas were terrible at very slow speeds, the 4000 (newest model) is not that bad.I believe it was 5x per sec update. I can get over the waypoints pretty quick.

I could'a swore that my Elite 5DSI GPS said I was moving at 0.5mph ... when I was playing with it on the lake, the ONE time I've been able to take it out & use it. I'm pretty sure I was under TM power, at the time, and not just drifting with the wind (or after taking my foot off the TM switch). I could be wrong, but I remember it being a pretty slow speed that was registering .. and I was impressed with the fact that it even registered.

... cp

I agree with Catfan. Marine inertial navagition systems aint cheeeeep. I worked on airborn inertial navigation systems in my oher life.

Check out Iphone apps for INS. Don't know how accurate they migh be.

The lowrance with LCG4000 external will track below .4mph as long as you are heading in a relative direction. Sudden changes causes hesitations in position on the map as described by Catfan. Takes the processor time to figure things out. You can add a Fluxgate compass to the nmea2000 for about 800 bucks. It shows which way you are heading instantly and don't care much about you speed.

Ment to add that Interphase Inc. makes a foward loooking sonar that could hlep.

Originally Posted by CatFan

Nothing is going to show you moving at .07MPH. Maybe you meant .7MPH?

The problem with any GPS indicating location at that kind of speed is that you are moving far less than the GPS error between updates. .7MPH is about a foot a second, and consumer GPS isn't accurate enough to even tell which direction you moved.

Sorry that should have been .7, But its funny that my hand held can do what a $2000. unit can't even come close to.
Also why can my Hand held show me moving and hold me over a spot the size of most peoples boat. But these units costing 5x more can't?

Guess I just need to do like I did years ago. mark spots on the bank in 3 spots and stay on a ledge in the middle of the lake. Rather then try and use this stupid stuff that can't even tell me I'm on water. Half the time both the 987c SI and the Matrix 97 like to show me up on dry land.

There is a long, long post on here about the donut in HB units. My HDS keeps me on my spots and works down to .4 mph. The Elite 5 that i sold had the same issue as HB, Lowrance's tech told me the HDS and Elite series use different GPS systems.

To really, really stay on top of a brushpile, I think you have to use a marker buoy. Personally I'd rather keep my eyes on the water and my fishing line, rather than back and forth between the line and a GPS. Paint your marker buoys grey, so they aren't so obvious. I also agree the Garmin GPS system is pretty dang good. My 498C is probably 6 or 8 year old technology, and it's dead on getting there. I never rely on it to keep me over a brushpile though.