On your boat, is your RF Ground connected in any way to your DC Ground? In other words, if you have a volt meter and check for voltage on your RF ground and any 12vdc post, do you read a DC voltage? Hope not, but if you do, then you might want to think about breaking that RF ground up so no DC voltage is present. How do you do that?
You cut the copper, or whatever you are using, at the point where the ground means a thru hull. Then you add four to six .15uF/630v capacitors where the cut is. You are now isolating the thru hull from the 12v. These are called DC Blocks. Why do you want to do this?
If you think about it, RF is not a DC component, it is an AC component. So the whole purpose of the RF ground is to help the RF signal not provide for a 12v return path. You really do not want any DC on that RF ground. Your coax cable and control cables have all the DC grounds they need.
So take a look at your RF ground from the tuner to any thru hulls. Check for any signs of galvanic corrosion. If you see it, it is because you have DC voltage and current going through that path. Eliminate that DC path with capacitors.
You cut the copper, or whatever you are using, at the point where the ground means a thru hull. Then you add four to six .15uF/630v capacitors where the cut is. You are now isolating the thru hull from the 12v. These are called DC Blocks. Why do you want to do this?
If you think about it, RF is not a DC component, it is an AC component. So the whole purpose of the RF ground is to help the RF signal not provide for a 12v return path. You really do not want any DC on that RF ground. Your coax cable and control cables have all the DC grounds they need.
So take a look at your RF ground from the tuner to any thru hulls. Check for any signs of galvanic corrosion. If you see it, it is because you have DC voltage and current going through that path. Eliminate that DC path with capacitors.