An elevated jack-up weighs 17,000 kips. Its center of gravity is located 110 feet aft of frame zero (AF0). What would be the new LCG if the cantilever (weight 900 kips) and drill floor (weight 800 kips) were skidded 70 feet aft?
• Longitudinal Center of Gravity (LCG) shift when a weight is moved longitudinally • Using a moment = weight × distance approach to find the total moments before and after the move • Remember that the total weight of the unit does not change when shifting weights internally
• How can you calculate the total longitudinal moment of the jack-up before the cantilever and drill floor are moved? • What is the effective weight being moved aft, and what total moment does that create over 70 feet? • Once you have the new total moment, how do you get the new LCG position relative to frame zero?
• Be sure you combine the cantilever and drill floor weights to get the total weight moved • Confirm you are using consistent units (kips for weight and feet for distance) when calculating moments • After dividing total moment by total weight, check if the resulting LCG shift is reasonable compared to 70 feet of movement and the proportion of weight moved to total weight
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