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Old 25 September 2006, 11:54   #11
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Originally Posted by Manos
What is the manufacturer of these props you are talking about guys?

Mercury Quicksliver Mirage
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Old 25 September 2006, 17:58   #12
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Anodic chalk

Limescale type deposits on propellers are characteristic of the anodes working well. Known as anodic chalk. Can't quite remember the chemistry but most well protected boats we look at have a film on the propellers (bronze or SS).
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Old 25 September 2006, 18:00   #13
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Not Just The Med

I have the same problem berthing in marina - laser 2


I was wondering whether it was to do with electrical issues ?? (all boats around are linked to mains)

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Old 25 September 2006, 18:45   #14
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Quote:
Originally Posted by Searider
Limescale type deposits on propellers are characteristic of the anodes working well. Known as anodic chalk. Can't quite remember the chemistry but most well protected boats we look at have a film on the propellers (bronze or SS).
Surely it should be known as Cathodic Chalk - since it forms on the cathode?

I'm speculating on the chemistry because I can't see an obvious way to form CaCO3 electolytically. So two reactions can occur at the cathode:

O2 + 4H+ + 4e- --> 2 (H2O)
O2 + 2 H2O + 4e- --> 4 (OH-)

this will result in a local increase in pH which will make CaCO3 less soluble.

doesn't help explain why sometimes it happens and sometime it doesn't though.
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Old 26 September 2006, 04:58   #15
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Thank you for the various sometimes quite scientific explanations

However as Polwart says none of them explains why sometimes it happens and sometimes it doesn't.

IMHO I think that it must be something to do with the quality of the SS metal that the prop is made of. I cannot think of anything else.

If however, someone knows please enlighten us.
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Old 26 September 2006, 05:13   #16
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Had a Honda 90 with SS prop.
In Croatia (Island Krk) had the same problem, solved it with Lime-Ex.
In St. Tropez, same outfit, same sea: no problem.
In the Netherlands, no problem.
??????????????????
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Old 26 September 2006, 05:23   #17
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Might there be local anomalies due to the geology, Croatia has a limestone coast I think (holiday there 30 years ago), as the tide isnt huge are there fast currents? if not then could lime leached out of rocks hang around?

Could the non misted props be on boats with poor anodes?
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Old 26 September 2006, 06:36   #18
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@Simon B: sounds logical. The mist on the prop looked like lime.
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