I’ve been having difficulties with mounting transducers on my pontoon. I recently installed a Lowrance Elite 5x and its working great until I hit about 8 MPH then the graph loses all depth reading and basically goes blank and says I’m in 1.4 feet of water regardless of depth. If I back off the throttle and slow back down it will eventually correct itself. I’m guessing the pontoon is creating some sort of turbulence that’s causing the false reading.  The unit is running off of a dedicated battery so I’m assuming it’s not electrical interference. Has anyone ever had a similar problem? I’m no sonar installation expert but this is getting old. Any help would be appreciated.

I have the lowrance elite 4x dsi, I also had the same problem when I installed on my lil aluminum boat. I lowered the transducer further into the water which made it better. Then I lowered the rear of the transducer a click or two to were the rear of transducer is slightly pointed to the ground instead of parallel to the ground as manual stated. This made it work like a charm will hold bottom no matter what speed.

Thanks Bonehead. I'll try tilting it like you said. If that doesn't help I'll find a way to lower it down deeper into the water.

 Can you look and see how it is riding in the water at the higher speeds? Maybe you can leave the tilt bolt a little loose so you can reach down and adjust it while on the water.

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Well the "mystery" is solved and I'm almost too embarrassed to say what the problem is Turns out as the boat gains speed the log is creating a "water void" behind it and the faster you go the larger the void gets. The transducer is coming completely out of the water. I'm going to rig up some kind of drop bracket  to get it down into the water. I'm not really excited about that because I envision it getting banged on everything and anything. I'm thinking I'll have to drop it another 8-10''.

I would be tempted to get a 3' long rod of 3/4 or 1" square alumimnum from Lowes, cut it in half, mount them side by side vertical on that livewell pump doghouse, and extend it down that way. You could even C-clamp them against that doghouse and do some test runs, to see what works best for the transducer, before you commit to holes. Just a thought. 

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The more you practice, the luckier you get.

I would find a way to move it from behind the pontoon, rather than moving it deeper in the water.

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You Can Tune a Piano, but You Can't Tuna Fish (REO Speedwagon)