gps accuracy

[dairyman]

this is a general question---I have a Humminbird 788ci with GPS. Is the built in GPS as accurate as the hand held GPS units,like Garmin or the others??

[kg2]

My HBs on my phone consistently say the estimated position error to be in the 9-11 foot range. Is this truthful? Seems to be.

I have both the 50 channel receiver and the high accuracy receiver on the Skeeter.

[Nick Kuhn]

The accuracy is pretty good, usually within 20 feet. However you will likely want to check the lake map offsets is something looks suspect. I know there's been several times going around a point on the water where the GPS trail has shown me driving over land.

[kg2]

My HBs on my phone consistently say the estimated position error to be in the 9-11 foot range. Is this truthful? Seems to be.

I have both the 50 channel receiver and the high accuracy receiver on the Skeeter.

I must have been doing multiple things at one time... My HBs on my Skeeter...not phone... (Or perhaps I am losing it.)

[Wish-I-Were-Fishn]

Was wondering about that

[delcecchi]

Naked GPS is limited in accuracy by various things. Adding a WAAS signal improves it considerably. With the right additional equipment on top of that you can get survey level accuracy.

[bobbymalone]

With the right additional equipment on top of that you can get survey level accuracy.

LOL, if you need to mark your fishing spot to the inch...

My garmin handheld will say the accuracy is +/- 11 feet when it's totally locked on. But if I have it point me to a waypoint and it says it's 0 feet away +/- 11 feet, I'm usually standing right on top of last weeks frozen over holes.

Personally I think 50 satellite receivers and whatnot is mostly a marketing gimmick.

[TruthWalleyes]

My HB898si on the diagnostics screen typically shows 2 or 3 feet.

Turn on your 798, go to diagonostics screen.

Or, turn on diagnostics screen and view at any time by pushing the view button.

The distance your transducerr is from your GPS receiver will also create error. i.e. your transducer is on the back of the boat and for some reason you put the gps puck on the front of the boat. Now every waypoint will be off consistently by your boat length.

[CaptainMusky]

The distance your transducerr is from your GPS receiver will also create error. i.e. your transducer is on the back of the boat and for some reason you put the gps puck on the front of the boat. Now every waypoint will be off consistently by your boat length.

This will pretty much always be the case because I dont know of anyone that has their transducer mounted immediately below where the GPS unit sits. So if it is at the console of your boat, its already off by 7 feet (depending on size of boat). You should be able to get within 15 feet of where your GPS was when you stored the waypoint, but again, depending which way the boat is pointing etc your depth could be considerably different.

[TruthWalleyes]

Mine is mounted within 6" of my ducer.

[h8go4s]

Mine is mounted within 6" of my ducer.

Mine too. Easy to do with an external GPS antenna.

[CaptainMusky]

Mine too. Easy to do with an external GPS antenna.

So if you move your unit to the front of your boat then all your waypoint are off by 12 feet then right? LOL

[h8go4s]

"So if you move your unit to the front of your boat then all your waypoint are off by 12 feet then right? LOL"

Captain, not sure what your point is here. With an external antenna mounted as close to the transducer location as possible, the depth reading will correlate to the GPS map location as accurately as possible. It doesn't matter where the "unit" is mounted. If your "unit" uses an internal antenna, then the GPS map location will be off by the distance between the antenna and the transducer.

Or are you just jerking my chain?

[CaptainMusky]

Quite simple actually. If you use an external antenna, move the sonar to a different location while leaving the external antenna in it original location it will be off. You will arrive at the waypoint when your antenna does so if that's in the back and you are in the front you will be off by the length of your boat. If you have an external antenna in both locations no issues. If you have an internal gps no issues.

[h8go4s]

I don't move my sonar to different locations. And you said in an earlier post, "I dont know of anyone that has their transducer mounted immediately below where the GPS unit sits." Well, I do and anyone who has an external antenna likely does also. So our GPS location relative to the sonar reading is about as accurate as it can get.

[CaptainMusky]

Good for you. Having an external antenna and mounting it near the tranducer isn't an automatic thing that many people do. I take it you have a tiller boat. Makes perfect sense to have things mounted as you do, but a console I don't think so.

[h8go4s]

Good for you. Having an external antenna and mounting it near the tranducer isn't an automatic thing that many people do. I take it you have a tiller boat. Makes perfect sense to have things mounted as you do, but a console I don't think so.

Why? I know this is splitting hairs, but the most accurate setup is to have the GPS antenna located as closely to the transducer as possible. With an external antenna, it doesn't matter where the DISPLAY SCREEN is located, does it? What you want is correlation between the sonar reading and the chart reading.

[CaptainMusky]

On a console boat where is the tranducer located? In the back right? So the depth you are reading and what you see on your display is at the back of the boat while you sit near the middle right? I am not talking about where you mount your antenna in respect to the display, the transducer. Your display will read mapping based on location which is obtained by the antenna regardless of where it is but if you try and correlate mapping to depth it will be off by the distance the antenna is away from the transducer.

[h8go4s]

On a console boat where is the tranducer located? In the back right? So the depth you are reading and what you see on your display is at the back of the boat while you sit near the middle right? I am not talking about where you mount your antenna in respect to the display, the transducer. Your display will read mapping based on location which is obtained by the antenna regardless of where it is but if you try and correlate mapping to depth it will be off by the distance the antenna is away from the transducer.

Exactly my point. Where you sit is irrelevant. With an internal GPS antenna, the distance between the display screen and the transducer is usually greater than it would be with a properly mounted external GPS antenna. It doesn't matter whether it's a console boat or a tiller boat, the transducer is either mounted on the transom or on the bow mount trolling motor. So to get the best correlation between mapping and sonar you want the GPS antenna mounted as close to the transducer location as possible.

[CaptainMusky]

Is your external GPS receiver mounted within 6" of your transducer? mine isn't since I have internal gps and everyone I know isn't either. That's been my point. Unless I am using the GPS by my trolling motor. At the console my GPS is 9 ft from my transducer.

[h8go4s]

OK, we're back to where I entered this thread three days ago:

Originally Posted By: TruthWalleyes

Mine is mounted within 6" of my ducer.

My reply was:

"Mine too. Easy to do with an external GPS antenna."

I feel like I'm talking to a wall. I'm done now.

[CaptainMusky]

If you wouldn't mind posting pictures of how you mounted your external antenna 6"away from the transom transducer I would like to see it. Never saw that on any boat professionally rigged or otherwise.

[Wish-I-Were-Fishn]

I think gps accuracy has a lot to do where you are fishing. I've had errors as high as 40' in some places on some days.

[Wish-I-Were-Fishn]

That's how some people run into islands in VNP.

[Nick Kuhn]

Not sure why you would need the GPS mounted near the transducer. I do most of my fishing closer to the console than the transducer. So what if the depth is off a few feet (and this would have to be on an extreme dropoff), you can intuit how deep it is where you are fishing.