Hi Chris,
Elbow grease and scrapers is certainly one way, and probably the way I shall at the beginning of next season for the underwater parts of the hull.
However, when I want to do a really determined hull clean, I might just consider buying
Dilunett again.
It was not cheap, when I used it in 2005, but was reasonably effective at taking paint off with the minimum of effort. You certainly can't use more conventional paint and varnish strippers as they tend to dissolve the resin in the hull.