Thread: 997 Gps

Originally Posted by crappielimits

Due to the accuracy of the gps, it isn`t going to matter if the puck and transducer are say 10 foot apart which is halfway of a 20ft boat. The accuracy is usually 10to15 foot for the gps and the clearer the view the better the signal. The gps gets you close and you use the sonar to fine tune.

Well, the way I see it is that if you mount the puck 10 ft from the transducer, you just added another 10 foot of error. Than could mean up to 400 square feet of water to search, That is a lot of water here.

Cane Pole is right. The linear (straight line) distance between the transducer and GPS receiver can make it harder to pinpoint that bit of structure you marked with a waypoint sometime earlier. You won't notice it if you are travelling the same direction when you are looking for it as when you marked the waypoint. Otherwise that 10 foot distance difference between the transducer and GPS receiver could put your transducer up to 20 feet away from the same structure if you were to looking for it while travelling in the direct opposite direction even though the GPS receiver shows you as being dead on the same coordinates. For the best possible repeatable accuracy the GPS receiver should be positioned over the transducer. This is especially true for any waypoint that was made while referencing sonar data. Now I wouldn't go mounting the GPS receiver in some location that would not allow it to find and lock on to all available satellites as this could cause it to be more inaccurate which could cause a difference of more than 10 or 20 feet.
Not all GPS-Sonar users will notice this difference in accuracy though. Some of this gets back to how we each use our GPS and sonar units, how the actual waypoint was marked, and the true positional accuracy of the GPS unit both when you marked the waypoint and when you were looking for it again.

In my case, I have a transducer at each end of the boat. I have the GPS receiver about midway between the bow and stern so the position error is about the same no matter which transducer I'm using to find what I'm looking for.

This works for me as I just get close with the GPS and use the depth finder once I get near the right spot. It is rare when I approach a waypoint and it does not fall within the SONAR cone so I can see it on the depth finder.

Well on the day I was talking about we were spider rigging and my partners $300 gps was sitting right beside the transducer and telling us we were moving about .3-.5 mph and my $2000 gps and sonar was saying we were going anywhere from 1.5 - 3 mph....makes you feel real good about your money spent....I'm gonna raise my receiver up above the transducer next outing and hope that helps....

Greg and Canepole, I understand what you are saying and it is better for say mapping, but for fishing most people mark structure and then line it up with sonar. I use a trans. at front and back to relate to structure. I can get dead on any structure I mark. I have both units hooked to one trans on the console this close to the center of my boat. NO interfence and it is out of the way of me and the water.

We've had this discussion many times on other boards. First, going over "all" the GPS manufacturer specs, the best "honest" accuracy they claim is around 10 foot and thats for 95% of the time will be printed in their manuals.
Unless your making extremely high accuracy maps, that likely won't be able to show that kind of detail any way, I tell my customers horse shoes and hand grenades. You should only worry about getting so close, then staying a good cast a way from it, you'll spook the fish.
WarrenMN