🔍 Key Concepts

• Effect of removing weight low in the ship on vertical center of gravity (KG) • Relationship between KG, stability, and free surface effect when tanks are empty vs full • Difference between deballasting double bottoms (very low tanks) and higher tanks

💭 Think About

• When you remove ballast from a very low tank, what happens to the ship’s overall center of gravity — does it move up, down, or stay the same? • Is ballast in a double bottom considered weight high or weight low relative to the keel, and how does removing such weight normally affect KG? • Think about whether the effect of deballasting a double bottom would logically depend on draft or is mainly a function of where that weight is located vertically.

✅ Before You Answer

• Identify whether double bottom ballast is below or above the ship’s original center of gravity. • Decide if removing weight below G makes G go up or down. • Consider whether free surface effect is greater when the double bottom is slack, full, or empty, and if that significantly changes the basic KG trend described in the choices.