Accurate speed reading

[jeweaver]

I have a Lowrance x75 with the paddle wheel speed indicator. At idle, the unit tells me I'm going 1.8 mph. At the same time, on my Garmin handheld GPS, I get a reading of 2.6. I'm leaning more towards believing the GPS. Anyone have any idea how accurate GPS reported speed is? My Lowrance does have a "calibrate speed" option so I could make it match my GPS. 1.8 to 2.6 is a somewhat significant difference when pulling plugs.

[18 inch Crappie]

It will be off at slower speeds but at higher speeds you will find it to be more accurate, you have to remember you are spinning a little wheel in the water, how accurate can that be? Your GPS speed is the speed you are going. I would not adjust the speed on your fish finder till you check it at higher speeds with your GPS. Say 20-30 mph, they are never accurate at slow speeds. Thats why they invented GPS just for trolling when fishing.

[jeweaver]

Thanks! That's the kind of info I was looking for.

[Rost]

Your gps is correct. Most of the time both your boat and fish finder speedometers will be off.

[BobT]

On a lake, I would expect a GPS to be about the most reliable means available. Remember too that the pick up wheel or pressure tube is measuring your boat speed relative to the water. In a river traveling against current these speedometers will indicate higher speeds than reality and vise-versa when going downstream. GPS is measuring your speed relative to your position on the surface of the earth however uphill and/or downhill may be less accurate because your relative position is changing at a different rate.

Bob

[Northlander]

Good point made that in rivers or current areas your wheel will be of a lot at times. GPS is the most reliable.

[LoonASea]

also the accuracy of your GPS can fluctuate depending on how many satelites its picking up,,, we had 2 garmin GPS units running last saturday in the same boat and they were different by .2-.5 mph but the accuracy also differed from 8ft to 22ft ,,,just some food for thought ,,,but I agree Your GPS will be more accurate then a paddle or tube reading

Randoid