Saildrive disappeared...

hi

bovine wrote: hi    why not run a lead from shore power to inside of your yacht and plug your heaters or dehumidifier that way your boat is isolated.              david

I also need to keep heaters in the boat during the winter and the way I see it my boat is isolated as long as the water heater is not connected. I will have to find out whether the charger actually connects the shore power with the water. The good thing is that I have a switch so I can turn it off. Does anybody else have that?

If I thought that it was not enough to pull the plug to the water heater I would definitely follow David's advice.

My boat's home port is in fresh water and I haven't seen any abnormal wear on the anodes. Judging by that I think I won't have to worry.

Johan

Health Warning: These thoughts are pub talk but I hope they will help.

2030
On the Volvo 2030D the gearbox and thus saildrive & prop is electrically isolated from the engine. So electrically connecting to the engine block does not electrically connect to the prop.

A surveyor told me. Volvo bronze props from 2002 to 2004 are prone to de-zincification (turns pink) due to an incorrect balance of the metals used in the casting. Yachts from Swedish builders quietly had their props replaced by Volvo.

Anode Erosion.
I have found the 3 section anode ring to the Volvo prop dissolve faster than the anode screwed to the saildrive. After 2 months of ownership, alarmed at the rate that the 3 section anode dissolved (later found to be gone in 6 months) I fitted a third hull mounted anode close to the saildrive and electrically connected to the top of the gearbox.

WRT to AC leakage to earth current
Voltage can get on to the equipment's casing thus earth protection wire by either a short circuit (high voltage and high current) or by insulation breakdown or leakage by tracking across a wet surface (low voltage and low current). In the case of a short circuit the earth wire takes the heavy current, protecting the human by keeping the casing at earth potential (near zero volts) and the fuse on the live or the Earth Leakage Detector (aka RCD) trips thus cutting of the AC power. It is the low voltage low current scenario that causes electrolytic erosion.

Zinc Savers are two heavy current diodes connected in parallel and facing in opposite directions.   A positive or negative voltage of greater than 0.7v on the earth wire causes each diode to conduct in turn. Thus the current due to a voltage of 0.7v or greater (50v is considered a hazard) on the earth line is passed through the diode to the to the substation earth via the earth wire and the fuse or earth protection device trips removing the power.   When a voltage on the earth wire boatside of the diodes is less than 0.7v the diodes do not conduct, thus stopping the path to earth the substation earth and reducing the chance of a circuit being made to create galvanic corrosion.

Cathodes not Anodes.
In conventional electrics the current is said to flow from positive to negative. However in electronics, the true physics/chemistry is used ie. Electrons flowing from the negative (Cathode) to the positive (Anode) is used. The zinc that sacrifices itself is technically a Cathode not an anode, in M.G. McDuff's literature (UK supplier) you will see that they refer to Cathodic Protection

Regards
Mike

Re-worded description of diodes connection 20/12/08

Edited by Brightside - 20 December 2008 at 11:15