A jack-up 210 feet in length is level during transit. The LCF is 140 feet aft of the bow. How much weight should be applied at the stern to re-level the jack-up if 75 kips is applied at the bow?
• Longitudinal Center of Flotation (LCF) and how moments are calculated about it • Moment balance: weight × distance on one side vs. the other side to keep the jack-up level • How to find the lever arm (distance) from the bow and stern to the LCF on a 210 ft unit
• First, calculate how far the bow and stern are from the LCF. Which distances do you use for the moment calculation? • Set up an equation where the total trimming moment forward equals the total trimming moment aft to keep the jack-up level. • Think about whether the weight at the stern must be larger, smaller, or equal to the weight at the bow, based on their distances from the LCF.
• Compute the correct distance from bow to LCF and distance from stern to LCF before doing any moment math. • Use consistent units (kips for weight, feet for distance, kip-feet for moments). • Verify that the sum of moments about the LCF equals zero for a level condition before choosing an answer.
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