Uninspiring title isn't it?

My daughter has just bought a narrow boat which is in need of painting
but is experiencing great difficulty getting the old stuff off. Some
people just say paint over it but there's quite a bit of pitting in the
metal which she'd like to clean out and fill.

What should she use - heat torches, chemicals or hundreds of hours of
elbow grease? - any help much appreciated.
--
Pete Barker