Re: Prop Shaft Electrolysis


Hi, everyone,
I hope you are all having a great sailing season.

My new C Drive has finally arrived and we are sorting out the reinstallation to be done in early Feb when I can be present.  Hallelujah!!!!

I have just started looking at the electrical system to find the source of the current leak...with the help of a British electrician who was highly recommended by the marina owner.  Here's what we've found so far:

1. With the 24v battery switch closed (on), and the 220V shorepower off (at the breaker on the switching panel on the engine room forward bulkhead), there is 3Volt DC between the bonding system and the negative battery pole.  This disappears when the 24V battery switch is opened (off).  When the 220V breaker is turned on, this voltage jumps to 6V, whether the charger is powered or not (at the 220V panel in the galley).  When the 12V charger is turned on, the voltage jumps to 9+V.  My electrician is pretty confused by this.

2. When measuring this voltage between the negative battery pole and the bonding system, if the 24V battery switch is opened (turned off), there is a spike to the full battery voltage of 27V which degrades to 0 V over a minute or so.

3. We also discovered that the bonding wires from forward of the engine room were not connected to the angle iron rails that support the engine, but rather went to the stainless "muffler" and to the engine, outdrive, and transmission.  The bonding wire from the zincs on the rudder is attached to the angle irons.

I'm going to do some more investigation this evening, but wondered if anyone had any ideas about what may be going on.

As usual, thanks ahead of time for any light you can shed.

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