Skeg Anode

[magpie]

I am looking for advice on how to fit a "stand alone"  anode on the skeg of my LM 24. The boat has a pear shaped anode attached thru hull connected to the rudder stock,  the shaft (electro eliminator) brush and engine. 

Thank you.    Harry.  Magpie. 

[pengwyn]

Hi Harry / Magpie,

the shape of the anode is mostly of secondary interest (exept that the shape might influence the flow resistance, so pear shaped anodes seem to be a good (but not the only possible) choice).
Specially when using DIY anodes (e.g. slices from a zinc-rod), you have to keep in mind, that zinc will vanish over time. It's advisable to use washers and fix the screws very tightly, to reduce the dissolving of zinc and keep the zinc stable in that area, not to loose mechanical and electrical contact.
Commercially available anodes will mostly have an iron core, where the zinc has been casted around, which is less critical in terms of shrinking and electrical contact.
Most important is a proper electrical contact to the metal-skeg. Paint, corrosion, antifouling, dirt might increase the electrical resistance between anode and skeg, which will make the anode become ineffective. The resistance should be checked by a multimeter and should be in the range of a few ohms.
The reason for using anodes, is to reduce electrochemical corrosion in seawater, by providing material which is " easier" corroded than structural materials (iron, bronce, etc.) and serves as a sacrifice anode. For that reason materials which shall not be corrodes and the sacrificed anodes need good electrical contact to the metal, to be protected. A functional anode becomes looking corroded - if an anode is unchanged after the season, most probably something is wrong (insufficient electrical contact)and the material to be protected was not.

For more detailed information concerning the underlying electrochemistry, e.g. why things are different for ships having an aluminium hull, why the kind of anode might depend on the salinity / conductivity of the waters please check : www.chemguide.co.uk/physical/redoxeqia/ecs.html or similar sources.

hope this helps



Pen Gwyn