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Radar vs. GPS

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Old 04-23-2002, 03:28 PM
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Question Radar vs. GPS

Per a prior thread it seems that the general feeling is that GPS is much more accurate than radar. Agreed
In the latest issue of PowerBoat Mag every boat test, not a few but all, showed the Nordskog GPS reading to be 1-3 mph slower than the radar. The same goes with this months Fam and Perf articles with the difference up to 5 mph. Which do you believe???
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Old 04-23-2002, 04:35 PM
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NordicHeat,
Radar guns are very accurate in an ideal situation. Unfortunatley, trying to hold a radar gun in a moving boat with wind coming straight at you is less than ideal. It also matters were the gun is pointed and the srength of the reflection from the target. Another factor is if they are pointing the gun at the water, or a stationary shore target. Water current can also effect readings of both measurments.
I like to think that the GPS is more accurate in a boating situation (biased)
 
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Old 04-23-2002, 04:38 PM
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Radar sucks for boats. Too many mathematical corrections and variables to be applied. GPS is what is is. No guesses no corrections. On land, with perfect circumstances, I'd rather have radar.
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Old 04-23-2002, 04:51 PM
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I have a stalker radar gun. It and most radar guns are very accurate. If I have a person on shore with the gun and I drive straight at them I get one speed. If the gun is in someone's hand in my boat I generally see a higher peak speed. Why? The gun is very sensitive. If you push it forward it will register whatever speed you push the gun away from you at. Trying to hold the gun still while trying to hold on in a boat at exterme speeds is very difficult and the result is an erroneous PEAK speed which is going to be high. The wind pushes the gun back and if the person pushes it back forward, the speed is off. I have seen 5 mph spikes in rough water, and it isn't because the boat is speeding up. It is because the guy holding the gun is getting thrashed. Because of this we radar from shore on an inland lake and seem to get very accurate and consistent readings. Notice the guys in the boating magazines are in the boat trying to hold the gun still in the wind as they rip along. I did install a GPS speedo this year so I will find out soon first hand what the diff is. My bet is they are within 1/10 of one another. Radaring from shore of course. Just my opinion as always.
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Old 04-23-2002, 06:12 PM
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WETTE VETTE has made good comments. It all comes down to radar is PEAK & GPS is average over a period of time.

I also have a stalker radar gun & when the water is total flat it is hard to get a reading because the radar can not find anything to bonce off of & get back to the gun.
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Old 04-25-2002, 05:16 PM
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Seems like all great observations.
TJ, My GPS (as all do I believe) will retain the peak speed which is good because it's hard enough to see when standing still let alone flying across the water. I will rarely ever get an eronious reading because the GPS is velcroed to the dash and can't move as will a gun in the hand.
As I noted, all test in PBM indicate a faster reading with radar. This is simply because it retains the peak speed which includes all movements and variables. It will not retain adverse motions such as the wind blowing your hand back; only the favorable motions of pushing your hand forward and any other favorable variable results in higher speed readings across the board.
GPS is supposidly garanteed to +/- .1 mph and is much less influenced by outside variables if any.
Even +/- 1 mph would be somewhat acceptable but last time I checked a gain of 3-5 mph will cost you a lot of $$$$$ and when I do spend it, I want to know for sure that I can accurately assess my efforts and cost.
GPS gets my vote.
Thanks for the input,
Dave

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Old 04-25-2002, 05:32 PM
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Am I mistaken I thought, when people radared they had a person in another boat or on shore sitting still and the boat passed by them and was radared. Is this not how the mags do it???
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Old 04-25-2002, 06:16 PM
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They shoot the radar from the passenger seat of the boat. I have done both (using a quality Stalker gun) and the gps was more accurate. The radar would vary in readings depending on how it was held, and at over 100 mph in a couple foot chop it is hard to hold still. Usually radar will give you higher readings than gps.
 
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