Got Bored...........

[Jerry Blake]

and added some more information to my "Getting The Most From Your Graph (Sonar, Sounder, Fishfinder Thangy, etc.)" post that I was supposed to finish a long time ago. Presenting bait at just the right depth seems even more important this time of year. Unless it's properly adjusted your graph may not be showing you exactly how deep the fish are that you are targeting.

This is what I added (so you don't have to read the whole boring thing again):

The very first adjustment you should make on your graph is for Depth Offset or Keel Offset. This is an adjustment to correct for the difference between the depth of your transducer and the surface or the difference between the depth of your transducer and lowest point of your boat that is apt to run aground. For fishing purposes you’ll probably want to make adjustments so your depth reading is the actual depth from the surface to the bottom of the lake.

The easiest way to accurately make this adjustment is to position your boat over a smooth, level, hard bottom and measure the depth with a tape measure or string with several ounces of weight at the bottom and a mark for a known depth. Then adjust your Depth Offset or Keel Offset up or down until your depth reading matches the actual measurement from the surface to the bottom.

Changing the Depth Offset or Keel Offset may or may not correct the Target Depths when using Fish ID or the Grid Lines on your screen depending on the graph you have. To find out, put a 2-ounce bank sinker on a length of fishing line or string that is marked at 15 or 20-feet and matches a Grid Line on your screen. Then lower the sinker directly under your transducer to your measured mark and see if the return from the weight shows up at the Grid Line of the same depth.

You can also check your Fish ID to see if the Target Depths are corrected by turning up your Fish ID sensitivity until fish symbols start showing up on the sonar return from your bank sinker. If the depth of the Grid Lines and Target depths are accurate then they have been corrected with your Depth Offset or Keel Offset. If not then you’ll need to mentally adjust for the depth of fish and cover returns if you want to know exactly how deep they are, which can be very important when crappie fishing.

[Quicksilver1958]

Excellent Stuff Jerry!.. Thanks for sharing

[Trihull]

Jerry

Are you saying there is an electronic adjustment on the sonar that can compensate for the distance, say between the transducer on the trolling motor and the surface?

I have read my manual (Lowrance X135) but have not seen this, and simply mentally compensate.

[Don G]

Jerry

Are you saying there is an electronic adjustment on the sonar that can compensate for the distance, say between the transducer on the trolling motor and the surface?

I have read my manual (Lowrance X135) but have not seen this, and simply mentally compensate.

Should be under "keel offset" in your manual...

[FisherMike]

Yep,, it's there.
Jerry,, isn't it just easier to measure from the water surface down to the bottom of the transducer then deduct that from your keel offset? Thats how I did it but maybe I'm all wet.

[ad1974]

Jerry....That whole article you wrote is great,very useful stuff.

[Jerry Blake]

Yep,, it's there.
Jerry,, isn't it just easier to measure from the water surface down to the bottom of the transducer then deduct that from your keel offset? Thats how I did it but maybe I'm all wet.

It should be that simple but I would check to make sure you are getting an accurate bottom depth reading and also make sure the fish and cover you are seeing are the depth you think they are by checking it with a sinker at a measured depth.

The transducer for my 797 is only about 14-inches under water but it takes +2-feet of Depth Offset to get an accurate bottom reading and everything else on my screen is still 2-feet deeper than displayed. I'm hoping they will correct that with the next software update. On my LCX17M adjusting the the Keel Offset accurately corrects the target depths for the Fish ID (which I keep turned off anyway) and the grid lines, which are very helpful for determining the depth of cover and fish.

[Trihull]

Thanks Jerry

Checked my manual and sure nuff there it was. In the example given in the manual they subtracted X amount, but since my transducer is mounted on the trolling motor, I believe I should add X amount. Does this sound right to you?

[Jerry Blake]

Thanks Jerry

Checked my manual and sure nuff there it was. In the example given in the manual they subtracted X amount, but since my transducer is mounted on the trolling motor, I believe I should add X amount. Does this sound right to you?

Yes, if you want the depth reading to be accurate from the surface to the bottom you would add for the distance your transducer is under water (and then check it by measuring the depth of water under your boat). Lowrance's "Keel Offset" directions are for adjusting for the difference between the transducer and the boat's keel or deepest part of the boat so you know how close you are to running aground but it also works for calibrating the distance from the surface to the bottom.

[Spiderman]

Jerry. How long have you had your 797 and what do you think about it?

The side imageing technology is going to make it alot easier to find your tops isn't it?