Because there is a possibility of fuel oil being discharged overboard from a full fuel oil tank, it is decided to transfer 25 kips from tank 14 to tank 13. See COASTAL DRILLER Sample Load Form Number 1 (Rig Move). What would be the change in longitudinal free surface moments?
• Free surface effect and how it is expressed as a free surface moment (FSM) in ft‑kips • How transferring liquid between two partially filled tanks changes the total FSM of the vessel • The data on the COASTAL DRILLER Sample Load Form Number 1 for tank 13 and tank 14 (FSM per kip or per % full)
• Look at the load form and identify the FSM values (or FSM factors) for tank 13 and tank 14 at the given loading condition. How does FSM depend on how full the tank is? • When you move 25 kips from tank 14 to tank 13, what happens to each tank’s FSM individually? Does one tank’s FSM increase while the other decreases? By how much? • After you find the change in FSM for each tank, how do you combine them to get the net change in longitudinal FSM for the vessel?
• Make sure you are using longitudinal FSM values (not transverse or a total GM correction). • Confirm you are using the correct FSM entries for the before and after conditions of both tank 13 and tank 14 (correct percentage full or weight in each tank). • Verify the sign and wording: the question asks for the change in longitudinal free surface moments and whether it is an increase, so be sure your final number and direction (increase vs decrease) match the choice.
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