My boat is burning through the Prop Zinc (AN230 Beneteau) at a rate of 1 per month. This has increased since the winter where the zinc was lasting 2-3 months. The marina checked for stray AC current at my slip and two slips from mine and found no stray current. Keep in mind it was only a clamp meter that only checks for AC stray current. My hunch is it is a stray DC current from the bilge a boat nearby. Any recommendations on what to do?