The DEEP DRILLER is operating at a draft of 60 feet. There is 11.5 feet of drill water in each of the drill water tanks (5P and 5S). What would be the improvement in KGL if 5S is filled from 5P?
• Effect of transverse shift of weight on list (KGL) • How transferring liquid between symmetrical wing tanks affects the vessel’s center of gravity • Difference between a partial load (free surface) and a full or empty tank on stability
• Think about what happens to the transverse position of the center of gravity when you move drill water from the port tank to the starboard tank. • Does the free surface effect increase, decrease, or stay the same after one tank is emptied and the other filled? How does that influence KGL? • Which formula relates the lateral shift of a weight to the horizontal movement of G, and how is that then related to the change in KGL?
• Be sure you know the vessel’s displacement (W) and the weight of drill water transferred (w) before using any GG₁-type formula. • Verify the transverse distance between tank centers (port to starboard) that the weight moves; this is critical to get GG₁ right. • Check whether the question wants the net improvement in KGL (before vs after transfer) and not just the intermediate GG₁ shift.
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