What is the purpose of ballast on a ship?

• A. To adjust instability, trim, and draft by adding or removing water ballast.
• B. To increase ship speed by altering displacement.
• C. To balance crew weight.
• D. To dampen waves and vibrations.

Answer: (D)

Ballast is used to control a ship’s stability, trim, and draft by adding or removing water ballast in ballast tanks. When ballast water is taken in, the ship becomes heavier and the weight is placed lower in the hull, which lowers the center of gravity and increases the righting moment. This helps the vessel stay upright in waves, improves fore-and-aft balance (trim), and adjusts how deep the hull sits in the water (draft). When cargo changes or port conditions require, ballast can be discharged to lighten the ship, raise the trim, or reduce draft to meet limits. The other options miss the main purpose: ballast is not primarily used to increase speed, balance crew weight, or dampen waves and vibrations (though ballast can influence motion to some extent, those are not its primary functions).