dcr

[dcr]

Hoping to travel the French canal and river system next year to the Med and have a query about the need to change the sacrificial anode on the saildrive leg from existing seawater version to fresh water type (magnesium).

The boat will only be on the tidal Seine for about 2 weeks so would appreciate any thoughts on whether this is considered necessary - ie: leave existing anode on all the way or change to Mag. type, but would this be seriously depleted during the time spent in salt water and not last our journey time of say 6 months in fresh water?

Presume that once down in the Med we will need to have the usual seawater anode.

Thanks,
dcr

 

[Quandary]

I keep our boat in fresh water, but because we spend much more than a week or two in the sea at a time, we continue to use zinc anodes. Magnesium anodes last only a few weeks, at most, in salt water. The zinc anode is susceptible to passivation, a coating which reduces its effectiveness considerably so we supplement the one protecting the leg with a hanging anode wired back to the leg casing. The hanging anode needs cleaning with rough emery paper at least once a month though I usually wrap a bit of tape round part of it and just peel it off if I do not have time to clean it. The zinc anodes on the prop corrode normally (ie rapidly) because they are cleaned by the rapid rotation of the prop. No problems so far.
So I am confident you could use your zinc anodes in fresh water for a couple of weeks without risk, the shaft or prop anodes will continue to clean themselves, it might be worth scrubbing a leg anode as soon as possible when you change back to salt water, it will be easier where the water is warm. If it is white rather than grey metal it is coated.

PS Some of the guys round here swear by aluminium anodes as suitable in both fresh and salt water but I have never been able to find them for VP saildrives or props.