Three most likely scenarios. The antenna sender is shot. There is a section of coating coming off your cable so you are losing the signal to the water or the RCA cable needs to be replaced. Moor subtroll parts can still be bought online. Step 1..... on land, walk off 100' of cable and check it for visual signs of losing the coating. Step 2, if the cable is fine, replace the RCA cable with new. These you can get original replacement parts from Moor servicing or you can get them at Radio Shack cheaper. If those two things don't fix problem, assume it is the sending antenna. You can check the antenna wire for continuance yourself if you have a meter. The antenna you will have to order from the Moor replacement service company.
esgdirect.com is the site