The COASTAL DRILLER, when underway was loaded as shown in Sample Load Form #1 (Rig Move). It is now preloaded at minimum air gap waiting for all settling to take place. The preload, weighing 7,191.7 kips, has LM 870,196 ft-kips and TM 2,158 ft-kips. What is the starboard leg reaction?
• How total vertical load (kips) on a three-legged jack-up rig is shared between the legs • How transverse moment (TM) creates more load on one side (port or starboard) and less on the other • Using moment = force × distance about the rig centerline to find individual leg reactions
• Start by finding the approximate average reaction per leg if the preload were perfectly centered, with no transverse moment. How many legs share the load? • Think about the effect of a positive TM: does it increase the starboard or port leg load? How do you know from the sign convention typically used on sample load forms? • Use the total preload and TM together: if you know the transverse spacing between port and starboard legs, how can you set up two equations: one for sum of vertical forces and one for sum of moments to solve for each side’s reaction?
• Confirm the number of legs taking the load and how they’re located relative to the rig centerline (bow, port, starboard). • Verify the transverse distance from centerline to each side leg, since this is critical to converting TM into a difference between port and starboard reactions. • Before picking an answer, check that your starboard leg reaction plus the other two legs’ reactions equals 7,191.7 kips and that the reactions produce the given TM = 2,158 ft-kips.
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