The Catalina 30 sailboat down in the harbor has a large zinc
plate mounted to the inboard diesel motor.  This keeps the
salt water corrosion mostly on the zinc and not on the boat's
other metal parts.

  I think this has to do with the way ions are exchanged.  Zinc
gives up the ions more freely than stainless steel does. The
zinc plate rusts first, then the rest of the metal rusts.

  Chemistry majors feel free to chime in.  I'm just an amateur. ;-)

  Could this technique be applied to the steel body of my VW?
I can get the zinc plates at the marine hardware store and bolt
them onto the frame of the car.

  BTW, I do most of my driving in fresh water. 

Thanks,
Jack    stafford@zenith.dnet.hac.com
'73 campmobile -   aka Land Yacht