LMS 520c

[bassassasin88]

Just installed an LMS 520c. Works great until I start going over 10 mph, then the bottom reading just doesnt look right (white lines going through it) by the way the transducer is transom mounted. Thanks.

[REEL_MAN]

Sounds like your transducer is to high and starting to come out of the water, try lowering it. Or it could be the location is where it is having air bubbles passing under it. You may need to move it.

REEL MAN

[bassassasin88]

Thanks I will try lowering it first. Doesnt sound like an electrical interference problem?

[SethV]

Does not sound like electrical interference.

If you have a glass boat, I would install a shoot-thru transducer.  Much better results at high speed.  I have no problem maintaining a good reading even in the low 70's.

If you have to stay with an external transom mount, make sure the water flow over the transducer is laminar, not turbulent flow.  Sonar won't work through air bubbles.

Seth

[Bender]

There is also a problem I have read about with one of the versions of software. Mine is running 2.4 and I lose bottom is somewhat shallow water with weeds and I lost it running 60 MPH yesterday in deep water too. It sounds like 2.3 is the most recent version that is supposed to be working.
http://www.lowrance.com/en/Products/Marine/Full-Size-SonarGPS-Chartplotter-Combos/LMS-520C/Downloads/LMS-520C-Software-Update/