I've a cast iron keel that has been rusting quietly under my boat for
the last few years. Most of the antifouling paint on the keel is on
rusty 'scabs'.
What is the best way of removing the paint and 'scabs' from the keel?
Ways I've considered so far include a circular sanding device (in an
electric drill) and an angle grinder.
Does anyone removed this type of rust before? What is the best way of
removing it that doesn't take forever and cost a fortune in abrasive
discs? Does on the those 'paint removers' with the spring steel tines
work OK or do they just take off the rust?

Whatever method you use if you end up with bright metal it is important to
prime it VERY quickly before the salt air gets to it.
I was chatting once to a surveyor who had supervised the antifouling of a
large ship. He noticed that a layer of ferrous chloride was forming less
than 2 hours of shotblasting.

And after all the responses, and with the keel now laying very heavily next
to my boat at the sailing club, I think a shotblasting and epoxy coating is
the way to go - many thanks to all who responded!

Artie