688ci HD DI GPS track/fix issue.

I upgraded to my first GPS model this past year and have used it on 2 bigger fishing trips at end of last year in Wisconsin and Canada. The main issue I have is the inconsistencies in the tracking and speed when slow trolling or sitting still. There is a small area near a jug in the water that we boat by regularly, every time within 3 feet, the tracks my GPS makes are no where close to eachother, in the 20ft range on locator it’s beyond both sides, so it’s off at least 30+ft, and will show it all over the place. Also while slow trolling and jigging the speed will fluctuate rapidly and often, and will also go intermittent try to a higher speed (2-6mph) all while I’m barely moving and show my track going off somewhere then slowly trickle back to where I’m at.

I have marked way points on a shallow reef in 12ft of water and go back to same spot to find myself a good distance away and in 32ft of water. Anyone have any insight on these issues? Other than it showing me boating on land when I’m in water, or just land because I’m in Canada and no maps are allowed to be made, I like the operation of the unit. But with this performance it makes the GPS rather useless. BTW, I can start the unit up in driveway clear of anything, get full signal and it’ll show speeds of .2-1.8mph and tracking all over the place up to 50ft around all while I’m not moving. It’s permanently mounted in my 16ft aluminum Lund Btw.

Thanks in advance for any insight.
Dan

Dan,
The slow-speed performance issues you’re having is fairly common with that generation of ‘birds, and the reason that many of us upgraded to units that allow the use of an external GPS “puck”. Unfortunately, the 688 is not able to accept an external puck, so if slow-speed data is important to you, consider selling that unit off and getting a unit that will accept the external GPS receiver.

HRG

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Internal GPS blows compared to the pucks.

Thanks for the replies guys. I wish I was able to find info on this before I purchased this unit. When I was doing my research I found really nothing but good reviews for this unit, including a few guys that owned it. I certainly didn’t expect the performance out of it comparable to the bigger better units that are on some of my friends boats we use on Erie or Miss that are insanely accurate on speed, but I didn’t expect the GPS to be essentially useless.

You noted the speed accuracy at low speeds is junk, and that I can deal with for the most part because in this boat we are typically either casting or vertical jigging, rarely trolling cranks/spinners. However what about the accuracy issue with waypoints and the tracks being so far off? Being that we vertical jig alot I like to mark waypoints where I am marking schools of fish or catching fish in more open water, having a place to return to. At this point this is no better than lining myself up on markers on land and taking a guess at it when returning.

For reference, I took a picture of the unit while it was running in my driveway, nothing over the top of it obstructing the view and it had been running for about 45 min. You can see how much travel there has been when not even moving, all of those tracks are from turning it on and not moving it in driveway.

I did contact Humminbird and they informed me that there is a software update available for my unit, which I plan to do take care of today once I go out and purchase an SD card and a SD card reader. However when looking at the patch notes it doesn’t address GPS readings ect at all, so I am thinking thats a quick answer to get me off their back for now.

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YOu can see your GPS accuracy on one of your screens. I’d check it out.

I have my puck mounted very close to my transducer.
Your GPS waypoints are going to be off at minimum the distance your unit is from your transducer. Food for thought.

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my 1198 went goofy on my at low speeds the mph went all over the place was driving me nuts and had to go off the ipilot remote for speed below 1.5. did not have any and gps problems but an update fixed the problem with speed jumping around. so it would be worth a shot. I had a 798 before with internal gps and worked great.

I can definitely deal with the distance that it would be off between transducer and head unit, I know they say its going to be off 5ft or so, hell I can even deal with 10ft off in reality. But to see tracks that are so far off consistently is aggravating, and marking spots with waypoints that are clearly not even close to where I thought I was when I set it makes it pretty pointless. The speed factor issue does not bother me nearly as much as the inconsistency in GPS readings and how far off tracks and waypoints are. This happens both in Canada and Wisc.

I went and got an SD card and reader, so hopefully I can get the update completed this afternoon and test it out.

In the mean time I fired the unit up, let it warm up and gather its satellites for a while and it has been fluctuating between 12ft error to 54ft error quite a bit.

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So the update didn’t change much of anything. I completed and verified the update, reloaded unit clear skies out front, let it warm up and start making a track. You can see in this pic there is a fluctuation of about 190 feet north and south and about 60 feet east and west. You can see how dropping a waypoint is essentially pointless with readings like this.

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Yeah that’s interesting. When i’m anchored tight to a spot for several hours, i can zoom in to the 20′ range and have a tight cluster of lines. Often the accuracy is in the 3′ to 12′ range.

Assuming your boat is outside with plain sight to the sky; this might warrent another call to HBIRD.
I’ve never focused on my 788’s (Internal GPS) performance too much, otherthan i have easily verified this year ice fishing with it that it’s pretty darn close. I have noticed that it takes quite a bit longer to load and it doesn’t like thick fog either. Other thing to note is i used to use my 898 in my truck ice fishing. Mounted on genz box and the puck too. I could put that thing on the floor of my truck with zero view to the sky and it’d still lock on and have great accuracy. My 788 doesn’t like to be in the truck hardly at all. Takes a while to lock on and frequently loses connection.
So major difference in GPS capabilities internal vs external puck.

Yea now that I am assembling information from this perspective I wish I would have gone with a higher unit, at least one that had an external GPS option. I have a hard time justifying spending so much tho because the Canadian lakes that we fish have zero map options and dont even show up with generic outlines on the factory maps on any of the units…which is crazy since its less than an hour away from Rainy Lake. Also our other big trip takes place in Tomahawk, WI and just have generic outline, which doesn’t even coordinate with unit, it always has me driving on land ect. There are upgraded chips available for the other 4 lakes in the Tomahawk area, just not Lake Alice which we fish. So I have a hard time justifying trying to sell this then spend so much more on an upgrade when I cant take advantage of any of the cool map options out there…even tho this GPS being so inaccurate is very frustrating.

DH
I have a 788ci and a 898 the 898 requires a puck the 788 does not. I do use my 788 for ice fishing and have noticed that it shows you moving when your not. But my 898 does the same thing. Now I have not tried to measure the degree of movement when standing still but I will and try to report to you. I also have a Garmin Colorado hand held that does the same thing. I also have an older Magellan Meridian Gold that I just love that shows 0 mph and no movement when standing still always.

What I really think is that The Magellan engineers wrote the code such that it does not display the errors of GPS when standing still or at low speeds http://www.gps.gov/systems/gps/performance/accuracy/

Under the best of conditions the above link states 4.5 meter accuracy (=11.5 feet) But I think that GPS units are more accurate when moving than standing still.

You got me thinking but I would not assume that a puck insures better accuracy that an internal antenna

I’m in process of installing my 788 in my boat next to my 898. Mounted it but didn’t power it yet.
Hooked up my 898 turned it on, and in about 12 seconds here’s what my screen looked like.

I’m not going to Ethernet link my 788 right away, so tomorrow I can compare them side by side and if all other boat improvements go well it’ll maybe see water too.
Will report finding.

Plenty happy with my 898’s lock on speed and accuracy though

Wooops photo

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Just curious have you gone into the GPS diagnostics screen to see how many satellites are available? Some areas just do not have good GPS signals.

My 788 and 898 are hooked up next to each other on the boat.
It’s laughable how much worse the 788 is compared to the 898. Laughably worse.

898 locks on almost instantly.
788 actually took about 10 minutes to lock on when i was on the lake saturday.

898 would show an accurate speed of .2mph
798 would show 1.2 mph. Horribly off.

Water temps were identical.

Accuracy about 3′ on the 898, didn’t look at the 788.

Internal GPS can blow me.

Anyone know if an 898 and 788 ethernet linked together will they each share the 898’s GPS puck? I’d really like to run my map in my 788, but with the performance reduction in GPS accuracy i’m not excited about yanking the mapping card out of my 898. Or, can i put a puck on my 788?

yes, the 788 & the 898 can share the puck, via the ethernet cable.

HRG

Sweet. Thanks!!!

Ethernet link worked perfectly to use the puck for both units!
Very nice!

Edit: post deleted….started a different thread, b/c I don’t want to hijack.

So I have done some follow up testing on a few different bodies of water. My accuracy issue appears to be slightly better now, maybe the update did help some. I fished with a friend of mine who has dual Lowrance HDS 5’s in his boat and when comparing the two tracks they were almost identical and I had no fade away as I did before when trolling at slow speeds. When moving at speeds over a few MPH our speeds were completely identical, the low end speed is still junk tho. Trolling at a locked 1.2mph on his unit shows .2-2.6MPH for me, so that is not even close to dependable.

One thing I have noticed that is odd is that no matter what I can no longer get an Estimated Positional Error number to show. If I scroll to the Diagnostic screen it will show all the satellites that are locked but will not show any EPE at all, if I repower the unit on it might show a random number, say 17ft, and flash that number non-stop on and off without changing the number at all. It also showed “enhanced fix” with no EPE in the middle of the lake and seemed accurate, so I rebooted it to see if I can get an EPE, it then only showed “3D fix” and was flashing 17ft as the EPE and did no change. This is what I saw with the Enhanced fix and no EPE…

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