Education... photographic identification of electrolysis.
Fit the SeaBis System - its the most economic way for you to protect your installation.
Fuel gauge.
6 weeks in the water. Electrolysis tracks from the body of the fuel gauge in the engine room, through internal tanks to the hull then to the nearest conductor to the seabed - the anode. Note the anode has not depleted. Its protective action has been swamped by the electrolysis. The current follows the lowest line of resistance - the weld.