Lowrance depth guage loses it's marbles

[oldbuck]

I have a lowrance 3500 that reads the depth ok when I'm stationary, but when we get underway it loses it's marbles - starts counting up by the hundreds and just keeps cycling through what appears to be random numbers.

fwiw we boat in depths from 5ft to 40ft, but the depth guage is often telling us it 250ft, 600ft, 750ft, etc

If we slow to a stop it usually doesn't recover unless I turn off the motor and restart (like when we're boarding a skier). Then it reads correctly again until we start moving, then it begins cycling through the ever-increasing random numbers again.

According the manual if it loses contact with the bottom it will read 999 so it doesn't seem like thats whats happening.

Not sure how to trouble shoot the transducer and/or lowrance unit - any thoughts?

thx,
-d

 

[tswiczko]

Re: Lowrance depth guage loses it's marbles

My hummingbird done a similar thing only on plane and it returns to normal when I stop. Their tech said it was because air gets under it when I am on plane and needs to be moved lower, then it broke the mount so I epoxied it to a trim tab and it seems to be ok now

 

[oldbuck]

Re: Lowrance depth guage loses it's marbles

my transducer is mounted on the hull near the centerline under the motor - so it should be pretty deep in the water at all times (heavy boat with 7.4L engine) - but thats an interesting idea tswiczko - I'll have to see if changing the trim angle alters the readings any.

thx,
-d