anodes for aluminium hulls

what do you use for catholic protection (anodes) for small aluminium hulls in salt water? I think hull and components have to be grounded to battery ? what about lightning? rod? to ground out hull? My computer corrects spelling, but not intent? Cathodic? is the POPE well Grounded?

 

This may help: http://www.fishnet.com.au/forums/viewtopic.php?t=115627&f=8

 

Oh, and you need to speak to the Pope about that !

 

You need magnesium anodes.

 

we always use zinc anodes here:

http://www.mgduff.co.uk/pdfs/commercial/ZINC_HULL.pdf

 

ABYC July 2008-2009 has a pertinent discussion.
2.10.2 Notes:3 Page 8 E-2
3. If magnesium anodes are used in salt water, the negative potential may exceed the 1200mv maximum recommended potential and create the condition for cathodic corrosion.

There is a table further on that lists metals and alloys in order of their Galvanic corrosion potential range in millivolts tested under a specific set of parameters and
zinc anodes show a corrosion potential of -980 to -1030mv and magnesium alloys show a corrosion potential of -1600 to -1630 mv

Therefore magnesium anodes are not the way to go as they are above the max recommended by ABYC

Immediately below zinc are aluminum alloys but since the boat is aluminum you need to be above the aluminum corrosion potential value. So zinc is what is required.