Saildrive disappeared...

Rubato wrote: Netzerab, I followed your explanation, most of us are well aware of the basics of electrolysis. However, at the end, where you mention that "A third alternative is to enable a local earth plane on board" I didn't understand the logic. Isn't this just moving the problem? It's an attempt to make another piece of metal the target of connecting the circuit, the same thing we try to do with the zincs. The same challenges exist, how to make that "other piece of metal" the target instead of the vital metal pieces of the boat.   Steve

The problem with shore power is the grounding wire. The grounding wire often has a DC potential due to several problems combined. Sometimes this potential can be much higher than the 1-1.5 volts that get eaten by the diodes in an galvanic isolator. In such cases the galvanic isolator is of little or no help. The problem is that you can't really know what the dc potential may be for a given day.

For those of us that do not have the money nor the space for an isolation transformer, there is another alternative called local earth.  It works like the earth in your home, but uses saltwater rather than the sand, clay or whatever is under your house. It is actually just a grounding wire connected to a piece of bare metal, usually copper, of a given area mounted under your boat and submerged at all times.

You can then safely cut the grounding wire to shore because you now has a local earth plane that would safely conduct any current trough the salt water and back to shore. The conducting capability of saltwater is excellent and it is a far better conductor than a questionable shore power grounding wire.

Since you no longer have a shore power grounding, you no longer have to be afraid of any dc potential causing electrolysis. There is no longer a permanent closed circuit between your boat and other shore power connected boats/shore power ground. But you still have a proper safety grounding that will save your life in case of a fault. The only difference is that a small part of the safety ground now uses salt water as an excellent conductor, but not conducting dc at alll times as before, just in case of a ground fault in some of your own electrical equipment, and then only ac. You are safe. Your boat are safe. Electrical faults in other boats no longer apply to you.

All you have to worry about is to keep your own electrical shore power system ship shape and preferably install a ground fault interceptor for instantly cutting off the ac current if there one day should be a ground fault aboard your boat.

Obviously this local earth depend 100% of the excellent conducting capabilities of salt water and the fact that the human body is not harmed from current flowing trough the water because of the very large difference in resistance between water and body. In fresh water the case is the opposite and even if your boat is still safe, a swimmer can easily be elecricuted. The low resistance path is suddenly the body. Current at low as 15-20mA is enough to kill a human.


Edited by Netzerab - 27 December 2008 at 14:59

Stephen,

Would like to know the brand of 'Tube Heaters' you refer to. I am looking for similar.

Thanks

Franko

This isn't really a generic Hanse problem (unless you can show the wiring was defective).  A "standard" Hanse should be OK, although it would be nice if galvanic protection was "standard".  But no other boat manufacturers I know of do this as standard.  Discussion on this site is useful to help us protect our boats better - but I think you have a weak case if trying to show Hanse is liable - unless, there is a specific wiring fault on your boat.