A floating jack-up with displacement of 15,000 kips has its LCG 108 feet aft of frame zero (AFO). If 400 kips are loaded at 120 feet AFO and 800 kips are loaded 150 feet AF0, what is the new LCG?
• Longitudinal Center of Gravity (LCG) is a weighted average position based on weights and their distances from a reference (frame zero). • When you add weights, both the total displacement and the total longitudinal moment change. • New LCG is found by dividing the sum of moments by the total displacement.
• First, what is the original total moment of the jack-up before loading, given its displacement and original LCG? • Next, how do you calculate the moment of each added load using its weight and distance AFO? • After adding the weights, what are the new total displacement and the new total moment, and what do you get when you divide one by the other?
• Be sure to use consistent units (all weights in kips, all distances in feet). • Carefully compute the original moment (displacement × original LCG) before adding new loads. • After adding the loads, verify that you used the sum of all weights and the sum of all moments when calculating the new LCG.
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