🔍 Key Concepts

• Free surface effect in partially filled tanks • How liquid movement affects metacentric height (GM) and vessel stability • Relationship between GM, righting arm (GZ), and rolling period

💭 Think About

• When liquid shifts in a slack tank as the barge inclines, does stability generally improve or get worse? Think about whether the vessel becomes ‘stiffer’ or ‘tender’. • If GM becomes smaller, what happens to the righting arm curve and the natural rolling period? Do they get larger or smaller? • Which quantity is directly increased by the virtual rise of G caused by free surface: KG, GM, GZ, or the rolling period?

✅ Before You Answer

• Be clear on the difference between KG (height of center of gravity) and GM (metacentric height). • Recall that free surface causes a virtual rise in G — does that mean KG is corrected up or down? • Think about which of the four options would represent a worsening of initial stability, consistent with free surface effect.