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→Ballast Stability
On a sail boat, ballast must counteract the lateral forces on the sails. Without this a sailboat will lay down in the water and capsize.
Ballast is usually placed in the keel, which acts as a lever, so you don't need as much weight below as above. The keel is filled with a high density material, such as concrete, iron, or lead. By placing the weight as low as possible in a sailboat (often in a large bulb at the bottom of the keel) the maximum righting moment can be extracted.<ref>https://en.wikipedia.org/wiki/Sailing_ballast</ref> <ref>http://www.wavetrain.net/boats-a-gear/458-modern-sailboat-design-ballast-stability</ref> However, this will increase the Roll Moment of Inertia, which can be avoided by distributing weight instead of concentrating it.
Adding excessive ballast will make the roll motion more aggressive and less comfortable. Extra ballast will reduce the roll angle but the return will be snappier with a higher roll acceleration and more conducive to seasickness. <ref>http://www.kastenmarine.com/beam_vs_ballast.htm</ref>