[Anonymous]

Hi All,

On my Bavaria 36 Holiday the stern anode is connected via a single cable to the sail drive there is no other cables coming off I realise that the sail drive is bonded by the bolts to the engine which as neutral earth connection my question is this right! as in the volvo penta hand book it states the sail drive should not be earthed? The reason why I am checking is the stern anode shows no sign of erosion and I seem to be getting a voltage of 24v between earth from the water heater to live on the shore power lead this will be earthed through the water to the engine. Any input would be welcome.
Thanks Mick

[Anonymous]

Hi Mick

Galvanic protection is a tricky subject but, in simple terms, the item you want to protect (the saildrive?) and the protective anode should be close to each other (in line of sight) and connected together by a stout copper wire. Connection to the battery or engine is actually irrelevant. When the engine is not running (assuming a standard Volvo set-up), the engine is isolated from battery negative (or at least it is on the later boats). It becomes connected to the battery (negative/earth) when the ‘ignition’ switch is turned on and a relay in the engine control box operates. It might be worth a quick ‘resistance’ check between engine and battery negative to confirm this on your boat (with the engine on and off).

If the anode is not depleting it means there is no galvanic action, which is probably good, so long as there are no obvious signs of corrosion on the saildrive itself.

Regarding the 24V observed between the heater earth and shore power, this could indicate a problem but I would need more info to understand what is happening. Is this AC or DC volts. Also, is it measured with a high impedance voltmeter (which can give spurious readings if no current is flowing). Secondly, did you have a battery charger in circuit when you observed the 24V or anything else that could be providing a circuit between the shore power and the 12V DC system? In the normal shore power set up on Bavarias there should be no connection between the boat 12V system and shore power earth.

Roger

[Anonymous]

Hi Roger,

Thanks for the prompt reply 😯 I am of up to the boat this weekend for a week sailing so will do some checks on the points you mentioned. As to the charger being switched on when I tested yes it was 🙄 the 24v was AC but that was using a £6 multi tester, the cable size to the anode from the saildrive I would say looking at the overall size of the insulation is about 1.5mm not stout.

Will let you know the results.

Thanks
Mick

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