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The other hand is the right one! Displacement is technically the weight of water that the boat displaces when floating... equal to the actual weight of the boat. (Archimede's law) Anything that weighs more than it displaces will sink.. (a chunk of lead, for instance)
The ballast is the portion of the overall weight that is in pure ballast form (a bolt on keel, or ballast loaded into a hull cavity) Ballast ratio is a general term that implies how tender or 'stiff' a boat may be. Ballast ratios generally range from .25 to .50 in production boats, running around .3 - .35 or less in more modern designs, whereas boats built 20 - 30 years ago often had ballast ratios in the .45-.50 range.
The actual characteristics will depend on keel design and hull form in combination with whatever the ballast ratio might be.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)