M2040, Valvanic Action

[BrendanChandler]

<font color="blue"> I had a new engine last year and after about 6 months I noticed that there seemed to be dezincificztion of the prop which had some pink patches. The anode was not seriously corroded. Somebody has since suggested that they MIGHT be caused by barnacles.
I fitted a galvanic isolator and also used brushes to 'earth' the prop shaft.

The Workshop Manual which I downloaded makes the point the gearbox should not be earthed.

Have I dropped a clanged in 'earthing' the propshaft?

Thanks again oh wise ones.

Brendan </font>

 

[VicMallows]

I assume when you say 'gearbox should not be earthed' you are talking about connected to a shore supply earth (which is connected via the galvanic isolator)?
Presumably the engine/gearbox/shaft/anode are all bonded? First thing I would do is check the resistance between prop and anode in case there's high-resistance somewhere. This is best done by passing a current of several amps DC and measuring the voltage difference. A simple resistance check with a meter is likely to be influenced by slight electrolytic action if connection is less than perfect (see if there's a difference when reversing meter connections).

Vic

 

[claudio]

Quick check is to use a 12V tail lamp connected to the prop other end connected to anode via a 12V battery

 

[spannerman]

To quote the Volvo workshop manual, ' the engine is electrically isolated from the transmission, under NO circumstances earth the transmission as this will result in serious damage to the motor by means of galvanic corrosion'.
So there you have it from the manufacturer, this means that the gearbox or saildrive should not be connected electrically to the motor block or form any kind of circuit with the negative side of the battery. The flywheel housing has special plastic insulating washers and gaskets between the housing and flange that the transmission is attached to.
If your galvanic isolator makes a circuit with the negative side of the battery then you will have problems.

 

[BrendanChandler]

Hi Spannerman,
I am still confused. Is the gearbox isolated electrically from the propshaft and if so should I bond the propshaft as I have done?

Brendan