A certain portion of stone, pig-iron, gravel, water, or such like materials, deposited in a ship's hold when she either has no cargo or too little to bring her sufficiently low in the water. It is used to counter-balance the effect of the wind upon the masts, and give the ship a proper stability, that she may be enabled to carry sail without danger of overturning. The art of ballasting consists in placing the centre of gravity, so as neither to be too high nor too low, too far forward nor too far aft, and that the surface of the water may nearly rise to the extreme breadth amidships, and thus the ship will be enabled to carry a good sail, incline but little, and ply well to windward. A want of true knowledge in this department has led to putting too great a weight in ships' bottoms, which impedes their sailing and endangers their masts by excessive rolling, the consequence of bringing the centre of gravity too low. It should be trimmed with due regard to the capacity, gravity, and flooring, and to the nature of whatever is to be deposited thereon. (See trim.)
As a verb, signifies to steady; as a substantive, a comprehensive mind. A man is said to "lose his ballast" when his judgment fails him, or he becomes top-heavy from conceit.