Calibrating depth

[Cyclones]

I’m new this year to boats and fish finders.  Have a helix 3gn megi si.  The depth it reads is what I consider to be fairly inaccurate.  It will read that I’m in 1.5 feet of water and I’ll check with a fishing pole and I can get my hand wet before the pole hits bottom.  Is there a way to calibrate the depth?  Or is a little play just the norm?  
 

[moguy1973]

Are there weeds below where you are doing this?  If so the finder will see the weeds and not the bottom.  If not, something is wrong with installation of the transducer or the unit is bad.  And not that this is the case, but you have to remember if the transducer is on your trolling motor, it sticks down in the water a foot or so, so you have to account for that distance also.

[Jigfishn10]

I'm by no means an expert but like @moguy1973 mentions above, I'm going with the installation of the transducer.

[Bankc]

Are you sure you have it set to feet and not meters?  

[Cyclones]

1 hour ago, moguy1973 said:

Are there weeds below where you are doing this?  If so the finder will see the weeds and not the bottom.  If not, something is wrong with installation of the transducer or the unit is bad.  And not that this is the case, but you have to remember if the transducer is on your trolling motor, it sticks down in the water a foot or so, so you have to account for that distance also.

It’s dealer installed, sits on the transom.  There are usually some weeds, yes, so maybe it’s reading those….

[Cyclones]

25 minutes ago, Bankc said:

Are you sure you have it set to feet and not meters?  

No, I’m not sure….and if I find out that’s the problem you guys will never know!

[Russ E]

sometimes fish finders can get confused in shallow water. Nearly every humminbird I have owned has done this. 

My humminbirds will occasionally give weird depth readings in 5 foot and under.

The readout will be off but the 2d graph will usually either be correct or show 2 bottoms. usually one around 2 foot and one around 10 foot. 

have you tried going out to water over 10 foot and coming back to shallower water.  This usually resets the depth and it works fine after that.

[Cyclones]

11 minutes ago, Russ E said:

sometimes fish finders can get confused in shallow water. Nearly every humminbird I have owned has done this. 

My humminbirds will occasionally give weird depth readings in 5 foot and under.

The readout will be off but the 2d graph will usually either be correct or show 2 bottoms. usually one around 2 foot and one around 10 foot. 

have you tried going out to water over 10 foot and coming back to shallower water.  This usually resets the depth and it works fine after that.

I’ll try that, thanks 

[Team9nine]

If you actually want to calibrate it, take a tape measure and slide out to a good clean and solid bottom in around 10 feet of water and then measure the actual depth and compare to what your unit is reading. From there, you can use the 'depth offset' or 'keel offset' feature, depending on exact unit, and adjust the depthfinder reading up or down to show/match that exact measured depth. Most likely the unit isn't accounting for the depth of the transducer in the water right now.

[Jigfishn10]

He's not off by a few inches @Team9nine, he's off by yards. Unless I read the OP wrong, he says he's reading 1.5 feet and he's sticking a fishing pole down and getting his hand wet before he touches the bottom. 

 

Now that I think of it, the unit must be reading the weeds.

 

Great post tho, I actually just did this adjustment last weekend after viewing Garmin's youtube.

[Team9nine]

Just now, Jigfishn10 said:

He's not off by a few inches @Team9nine, he's off by yards. 

 

Great post tho, I actually just did this adjustment last weekend after viewing Garmin's youtube.

 

I get that, and it could be for a variety of reasons that his is off so much. Not unusual in shallow water as was mentioned, but I was more responding to his topic title and request for how to calibrate a depthfinder. I do it to mine as nothing bugs me more than to have my front and back units on at the same time and them showing a foot and a half depth discrepancy between them because of where the transducers are mounted and how each unit reads and interprets depth - lol.

[Jigfishn10]

Ah, gotcha mi amigo...just another senior moment on my part.

[Cyclones]

7 hours ago, Team9nine said:

If you actually want to calibrate it, take a tape measure and slide out to a good clean and solid bottom in around 10 feet of water and then measure the actual depth and compare to what your unit is reading. From there, you can use the 'depth offset' or 'keel offset' feature, depending on exact unit, and adjust the depthfinder reading up or down to show/match that exact measured depth. Most likely the unit isn't accounting for the depth of the transducer in the water right now.

Dumb question……can I do this sitting in my driveway with the boat on the trailer?

[Scott F]

Transducers only work in the water.

[Team9nine]

1 hour ago, Cyclones said:

Dumb question……can I do this sitting in my driveway with the boat on the trailer?

 

If you know how much to adjust the setting up or down, you can do that in the driveway, but the only way to guarantee how much you need to adjust so you're reading exact is to get a measurement on the water. You can get close sometimes just using the waterline on the boat compared to the bottom of your transducer, but that won't answer the question of if your unit is truly reading wrong to begin with. If you just move out from the ramp over deep water and back and the unit tracks and shows such, you're probably fine and can shortcut if you want...or just leave "as is" as the foot or so difference usually isn't a big deal to most people.

[txchaser]

Mine was doing that sometimes in the weeds too. H'birds answer was something like "yeah it does that, sonar is bouncing off the weeds, nothing you can do about it." I do notice it is more likely to happen when I'm still. 

[Cyclones]

5 hours ago, txchaser said:

Mine was doing that sometimes in the weeds too. H'birds answer was something like "yeah it does that, sonar is bouncing off the weeds, nothing you can do about it." I do notice it is more likely to happen when I'm still. 

Yeah, it just freaks me out as a new boater when I’m fishing and i look at the helix and it says 1.5 feet.  I’m mostly worried about the trolling motor.  Funny, when I get those low readings I’ve never hit the trolling motor, but way too many times just slowing trolling around I’ve found the bottom or timber with it.  Maybe if I snap it off the wife will let me buy a TM that’s easier to deploy and stow than the freaking Power Drive model 

[BigAngus752]

19 hours ago, Team9nine said:

nothing bugs me more than to have my front and back units on at the same time and them showing a foot and a half depth discrepancy between

Hallelujah and Amen!  "Why am I always fishing on a slope?  Where are the flats?"

[txchaser]

On 7/31/2021 at 7:08 AM, Cyclones said:

On 7/31/2021 at 1:17 AM, txchaser said:

 

Yeah, it just freaks me out as a new boater when I’m fishing and i look at the helix and it says 1.5 feet.  I’m mostly worried about the trolling motor.  Funny, when I get those low readings I’ve never hit the trolling motor, but way too many times just slowing trolling around I’ve found the bottom or timber with it.  Maybe if I snap it off the wife will let me buy a TM that’s easier to deploy and stow than the freaking Power Drive model 

Good news and bad - probably a bunch of flex in the shaft, it'd be pretty hard to bust off.