upon haulout of my sailing boat I observed a large number of small pits on the 3 propeller
blades, mainly the backward facing blades.
It is a european boat (Jeanneau): all through hulls are unbonded. 12V ground is the engine
block. This has 1 copper mesh connection to the bronze (underwater) propeller
1 ball anode on propeller shaft close to the propeller
1 anode on the propeller nut
2 zinc disc anodes both sides of the bronze propeller shaft strut (that I added when connecting also the RF-ground of my SSB's antenna
tuner to this strut => this connection has DC-blocking capacitors 1 microF and the SGC tuner is reported to already have DC-blocking caps in its RF ground lead).
All this anodes have well worked after 12 months season: the ball anode was well eaten away (time to replace) - 1 of the disc anodes well eaten away - the anode on the propeller nut has worked a bit but still in good shape (will replace anyhow).
It seems to me the anodes work well to prevent galvanic corrosion
Hence I suspect electrolytic corrosion? Due to straw currents?
A guy doing the maintenance
sailing boats advised:
1) cut the ground lead of the shore power
cable (WHICH I WOULD NEVER DO!!!!!!)
2) connect a heavy duty copper wire to the engine
block negative, hang overboard
with a heavy zinc anode conncted to it when in the dock
stationary and on shore power
(doubtfull? but maybe useful in case of straw current
European boat => the shore power ground is NOT connected to the ships 12V DC ground in any direct way.
I could only suspect 2 devices:
a)the shore power battery charger
(it is a modern Mastervolt HF charger) - does it connect the shore power ground to the 12V DC ground?
b) the water
boiler also has a 220V heating
system (used very seldom so it is alwas physically plugged pout) - could it be faulty without tripping or connect the shore power ground to the engine block via the cooling
fluid that runs through the boiler to heat water
when running on engine?
Please your advices?
What could I measure?
(before maybe deciding to invest in an isolation transformer that maybe is unnesseceary in my case)