b393capt wrote in
ups.com:

What action should I take ?


NONE! 50ma is nothing! You're seeing the current between the zinc anode
and all the underwater metal it is PROTECTING! You have a zinc anode and
a some-other-metal (brass, stainless, etc.) prop/shaft/skeg/etc. The
direct connection of these creates a SHORTED BATTERY in a salt water
electrolyte. The small emf this produces creates the current that you
are measuring, which is attempting to PLATE the boat parts we want to
save and EAT the fish, which is exactly what we want because that's what
makes it work. The readings you're seeing are wonderful!

(PS - you cannot make resistance readings with any meter in the presence
of an external voltage (the EMF the fish/prop battery is producing).
NEVER connect your ohmmeter to ANY source of voltage which may destroy
it...ok? Thanks.

Larry, Electronic Metrology since 1965
--
Grade School Physics Factoid:
A building cannot freefall into its own footprint without
skilled demolition.