Author Topic: Depth on my 998c is not reading correctly  (Read 10169 times)

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Offline Mako Greg

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Depth on my 998c is not reading correctly
« on: May 07, 2012, 10:17:04 PM »
Hey folks,

Just got a new 998c and Im having a bit of trouble.  I was fishing a trout tournament and the depthfinder was going from 200 feet (which was correct) up to less than a foot while were drifting at a mile an hour or so.  It would suddenly read correctly after a couple minutes.  The down imaging and regular 2d sonar would show wild clutter then clear up as the depth came back to normal.  Any ideas? 
92 Mako 181 Flats
Humminbird 998c SI


Offline newkid4si

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Re: Depth on my 998c is not reading correctly
« Reply #1 on: May 08, 2012, 12:06:12 AM »
Mako Greg
     Any chance that you drifted over some baitfish or minnows near the surface?

             Mike

Offline Humminbird_Greg

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Re: Depth on my 998c is not reading correctly
« Reply #2 on: May 08, 2012, 09:51:36 AM »
Mako Greg,
Did this clutter come and go with something on the boat turning on and off?  If not than I agree with Mike in that it could have been baitfish near the surface.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline ITGEEK

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Re: Depth on my 998c is not reading correctly
« Reply #3 on: May 08, 2012, 10:13:42 AM »
Erratic depth readings could be interference from something
else on your boat (main motor, another sonar).

Have you checked your transducer mounting for tightness, and attitude.
The transducer should be flat against the water with your boat fully loaded.
Also, debris (weeds, fishing line), on the transducer might show weird things.

Offline Mako Greg

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Re: Depth on my 998c is not reading correctly
« Reply #4 on: May 08, 2012, 01:05:57 PM »
My raw water intake for the baitwell is a couple feet in front of the transducer.  I knew it was there when I mounted it but it never affected my old transducer.  This one may be more sensitive.  Its funny, i took it out for a test run after I installed the system, and it ran perfectly.  I can check the alignment this weekend.  Something could have shifted, but its unlikely.  Its tough to align on the trailer!
92 Mako 181 Flats
Humminbird 998c SI

Offline Mako Greg

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Re: Depth on my 998c is not reading correctly
« Reply #5 on: May 08, 2012, 01:19:29 PM »
If it were baitfish, I would have seen them.  Its a very clear lake and was a very sunny day.  Plus, the problem was very persistent.  That would be a ton of bait!

Good point about other things running.  I did see evidence of disruption when running the trolling motor at higher speed.  I know thats turbulence from the prop since it has a separate power source.  I have the unit wired into the electrical bank under the console which provides power for several other things on the boat.  There might some interference there.  I may need to bring another battery on board to test.

Good points guys.  What else should I consider?
92 Mako 181 Flats
Humminbird 998c SI

Offline ITGEEK

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Re: Depth on my 998c is not reading correctly
« Reply #6 on: May 08, 2012, 03:25:26 PM »
Interference is most likely your main problem.
A separate power source can still cause interference, if the
wires are too close to your sonar wires.

You should consider wiring your 998c to it's own battery
with nothing else hooked to that battery.  It doesn't have
to be a big battery.

Also, try and run the wires to/from the 998c away from other
electrical wires.  If you have to cross wires, cross them at right angles
like a cross.

I would eliminate all interference first, then see if there are other
transducer issues from your prop and/or water intake.
« Last Edit: May 08, 2012, 03:27:49 PM by ITGEEK »

Offline newkid4si

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Re: Depth on my 998c is not reading correctly
« Reply #7 on: May 08, 2012, 10:32:28 PM »
Mako Greg
          "If it were baitfish, I would have seen them.  Its a very clear lake and was a very sunny day.  Plus, the problem was very persistent.  That would be a ton of bait!"
           Pretty much eliminates my possibility. See how easy this is. Only a hundred more to go.

           Originally had my 998 powered by the cranking battery. Installed a separate battery this spring and electrical interference from alternator is gone.
           Other than the cost and weight, a dedicated battery eliminates many potential sources of problems.

                      Mike

Offline Mako Greg

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Re: Depth on my 998c is not reading correctly
« Reply #8 on: May 09, 2012, 09:51:35 PM »
Thanks for all the tips.  Right now it seems like the best thing to do is to get out on the water and troubleshoot. 

Come to think of it, the one thing i was running that day that I wasnt running during the test was the VHF radio.  It was on all day and the unit kept fouling up most of the day.  We may have a winner with that one. 

One last question...  How deep can I run and still get a good sonar return?  I was on a pretty deep lake, in the neighborhood of 250 feet sometimes.  Pretty steep initial learning curve on this unit, but its going to be worth it after I put the time in.
92 Mako 181 Flats
Humminbird 998c SI

Offline newkid4si

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Re: Depth on my 998c is not reading correctly
« Reply #9 on: May 09, 2012, 11:43:52 PM »
Mako Greg
         I have been able to clearly mark sunken boats in 50 FOW.
         The deepest local water is 60'. I'm guessing 100' will be pushing the SI limit.
         HB Greg will have the best answer.

               Mike

Offline ITGEEK

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Re: Depth on my 998c is not reading correctly
« Reply #10 on: May 10, 2012, 07:15:30 AM »
According to the specs of the 998c:
 The 2d sonar is good to 1,500 feet.
 The Side-Imaging is good to 150 feet.

Offline Humminbird_Greg

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Re: Depth on my 998c is not reading correctly
« Reply #11 on: May 10, 2012, 09:10:34 AM »
Depending on the slope of the bottom, what it is made of and the water quality will determine just how deep the sonar (2D or Si) will work to.  Ive seen a deep water Si image of some trees at 180+ feet but I would think that was the exception.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline sonar2000

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Re: Depth on my 998c is not reading correctly
« Reply #12 on: May 10, 2012, 04:09:13 PM »
It also depends on the target of interest. If you are looking for a sunken boat then 150 SI is good. If it is a smaller object like mansize then maybe 40 to 50 feet max.

Chuck

Offline jexeri

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Re: Depth on my 998c is not reading correctly
« Reply #13 on: July 18, 2012, 07:53:07 PM »
I've had some recent issues that are similiar.  My graph will read perfectly then I'll get up on pad and sometimes the graph goes to read a depth of 2', a thick black line goes accross the top...  even if the big motor is off and I have nothing else in use it will periodically go from reading perfectly to reading only 2' again.   I tried turning the sensativity up, down and back to default settings and it still happened.  I checked the connections to the back of the unit and they are solid.  The tranducer is on the outside on the hull, it has just a little (like barely moves up and down) give, but nothing that seems substantial. 

Anything else I should be checking?

thanks in advance

Offline ITGEEK

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Re: Depth on my 998c is not reading correctly
« Reply #14 on: July 19, 2012, 11:35:45 AM »
You can't expect your unit to work well when on plane.
Depending on your boat and motor, the transducer may actually
be out of the water when on plane and/or have so much turbulent
water around it that it won't work properly.

Losing readings at speed is one of the major complaints with sonars.

If this is happening with ONLY your sonar on in your boat, I would
first load test your battery.  The voltage may be fluctuating.

Secondly, if possible tighten your transducer.
I don't think it should have any play in it.

Thirdly, with your boat on the water, and fully loaded, your transducer
should be more or less flat against the water.

Offline Humminbird_Greg

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Re: Depth on my 998c is not reading correctly
« Reply #15 on: July 19, 2012, 12:03:08 PM »
jexeri,
We need some additional information about what is happening with your unit:

Does this only happen when you get your boat up on pad or does it also happen when idling or when using the trolling motor?

Do you have another sonar unit on the boat and if so, does this happen only happen when it is on or does it happen when it is off as well?

What water depths does this happen in?

Some things to check and try:
Make sure that your unit is running the latest software version.
Try adjusting the Surface Clutter menu to a higher setting (the Sensitivity menu does not affect the water depth readings).
Set the Water Type menu to the Salt (deep) menu setting.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline jexeri

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Re: Depth on my 998c is not reading correctly
« Reply #16 on: July 19, 2012, 07:06:42 PM »
I'll try the surface clutter settings as I haven't tried that yet.  I'll double check to see if I have the latest software downloaded too.  Good suggestions. 

to answer some of your questions it happens when on plane and idling, but also is happening when I turn off all other electronics in my boat and am not running the big motor.  If I'm essentially drifting it will work for a while perfectly, then all of the sudden with no change, wave activity, etc it will switch to 2', and then a few minutes later go back....

It hasn't to this point mattered what depth I was in, it's happened in everything from 4' to 44'....

also, in addition to the SI transducer that is mounted on the hull below the jack plate there is a glassed in transducer.  It almost seems like that tranducer isn't working or has come loose.  I'm not sure why (or if it would) it would still work at times though if that tranducer wasn't working at all. 


Offline Humminbird_Greg

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Re: Depth on my 998c is not reading correctly
« Reply #17 on: July 23, 2012, 12:19:23 PM »
If the Surface Clutter menu changes do not help; try plugging each transducer directly into your 998c Si unit and see if one or both show the same thick black line at the top.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline jexeri

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Re: Depth on my 998c is not reading correctly
« Reply #18 on: July 23, 2012, 07:15:10 PM »
I downloaded the last software update and adjusted the surface clutter down a few notches and that took care of it.  I didn't realize the latest versoin was just a few weeks ago.  I'll have to pay closer attention to that moving forward.

thank you for the help


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