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I get all kinds of marks on my new(ish) depth recorder when running very much beyond trolling speed. The faster, the worse. I have Cummins 6bt's. I thought a surpressor on my unit's power line would do it but have been told I would need one on each of my alternators. No problem on my radios or my chartplotters. Any thoughts?

Alternator issues are sometimes a condition of a bad diode in the unit increasing ripple and the other is increased circuit impedance. IE corrosion on wire connections.

The rf may not always affect all electronics depending on how the electronics are bonded and whether there are induced ground loop issues.

Using filter capacitors can be tricky matching the capacitance of the filter cap to the frequency of the noise.

Don't be dissapointed if it doesn't stop without trying different value capacitors.

Mount right at the alternator.

I'd check the affected units power and ground/bond connections first.

Walter, Where are your Tducers located? Could be an aeration problem rather than an electrical issue..just a thought. BH

Walter,
Make sure that the transducer face is clean and the protective plastic stick-on is removed, I've seen brand new x-ducers not work correctly because someone didn't remove the protective covering. If that's not the problem try using some dish washing liquid soap on the transducer face, wash it off good, aI have had x-ducers show lots of marks if the water is real dirty or silty. Also try turning down the gain and make sure of the setting if it's a dual transducer( either 50Hz or 200hz) sometimes the selector sticks on the wrong setting. Is the transducer in the same place as the old one, with no obstructions across the transducer face from a bubble trail.
Pete