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You said your transducer is floating good. Stupid question from me,Did you look down the hole and see if it was past the bottom of the hole? Might through your reading off by a smidge by showing a false reading or in your case not seeing a rather large jig. Also look to see if trans is sitting square in your float. Not kittywhumpus by a smidge.2 cents
What degree ducer do you have? I don't fish deep water but I notices a huge difference in signal strength when using a 9 degree ducer over a 19 degree ducer. The 9 degree gives a much stronger signal with less gain than the 19.
At 100 ft. plus te little to no current on the top water column could be different below.Try taking a large heavy spoon and lowering it down if you can follow the spoon on its way to the bottom without losing it than the no current is likely correct.Bring it back to the surface and change your bait back out. Lower your jig/spoon or bait down with a stop every 20 to 30 feet and locate a good signal again on you offering. If you lose sight of your bait with a vex or simular it will sometimes take a fair ammount of time to relocate.Do you use multiple holes with the Vex or fish the same one that your transducer is in. You may want to drill a lead hole or two for the transducer. If you think the current is going in a specific directiontry drilling the second hole 2-3 feet away in the direction of the current. Drop in the transducer and see if you can pick up your bait.There is no current in either lakes that I'm fishing.A friend has a FL- 20 and is having the same problem ,We took a FL- 18 and tried it out in the same hole with the same bait and it picked up perfect. I also tried a Humminbird 55 in the same hole and it did not pick up the bait,switched to a large pimple and that helped.Both units says it has a 1/2 " definition and will read BOTTOM at 200'. I'm thinking either the 20 or the 55 is not meant for water much deeper then 100' with bait 3' or smaller,but then why did the 18 work ? I contacted Humminbird and after I gave them all the info that I have posted here they said to keep a log the next time that I used it and call them back with the info and Vexilar said to send the unit back when I could.I've got $1,000.00 worth electronics sitting here that are both advertised as the best on the market but can't pick up a 3' bait at 100' I'm not happy nor would I recommend either unit to anyone who fishes deeper water FF