Galvanic corrosion

[slec777]

Good morning

I have a 48 ft fibreglass sailboat. Contest 48.
Last season I noticed small pitmarks on the cast Iron keel, and some rust.

I fitted a Zinc anode by drilling a hole through the trailing edge and bolting a 100mm anode, with a stainless steel bolt

I have just lifted her out after 15months in the water and the pitting is significantly worse and the area around the through keel bolt has disintegrated to a lead pencil type texture. The bolt is fine.
I fear I have caused the problem to worsen by creating a new galvanic interface. Whoops!
Hopefully this is not fatal and I will just have one season's worth of corrosion.

Is there something I should do? , just not repeat the error? Thank you

 

[Tranona]

Yes. you have created a localised galvanic cell. There is no need for an anode on a cast iron keel. Most of the pitting is just rust, although you can get localised pits from impurities in the casting . So get rid of the anode and if you want to protect the keel long term have it blasted properly then immediately coated in epoxy.

 

[vyv_cox]

It is a waste of time and money to add an anode to a keel. The anode area is very small in comparison and any benefit will be localised. Paint is far more effective.