Definition:
A system used in some trailerable sailboats without a weighted fixed keel. Ballast (weight near the bottom of the boat) is needed to keep the boat upright when the wind pushes the sails over. In a water-ballast boat, a chamber in the bottom of the hull fills with water to provide this ballast. This water can then be emptied when the boat is put on a trailer, to make it lighter for easier trailering.
