A hard bilge
is sharply rounded where the keel
meets the hull
, which generally creates more initial stability. A soft bilge
, conversely, has a much more gentle curve. Soft-bilged boats are more easily healed at first, so soft bilges are sometimes called "easy" bilges, while hard bilges are sometimes called "firm" bilges.
A hard bilge tends to be a more modern design, thanks to the evolution of fin keels, which invariably involve hard bilges.