Erosion of the shaft/prop zinc is typically caused by one of two scenarios: stray current
around adjacent boats from an improperly or poorly grounded shore power
circuit or stray current induced from a bad or corroded ground on your boat
. If you are on a mooring
, obviously the first cause is moot.
Fixing the problem is not that easy to explain as it depends on what circuit(s) is/are dysfunctional and can only be identified by examination.
If you are constantly connected to shore power
and do not have an isolator or isolation transformer, there are simple tests to determine a shore power ground fault which bears reading up on.
If you are constantly on a mooring
, start inspecting all your wiring
for a bad ground starting with the bilge pump
wiring and the existence of any voltage potential between separate grounds on the boat.
Without knowing more of the above, it's impossible to pinpoint the problem which can be causing more damage than simply eating your zinc. Simply putting on more or a bigger zinc will only serve to exacerbate the problem.