A semisubmersible in transit is at a draft of 19 feet. The depth of the lower hulls is 21 feet. How much bunker fuel at 54.0 lbs/cu ft could be taken on and still provide one foot of freeboard if the TPI is 52.3?
• Freeboard change and TPI (tons per inch immersion) – how many inches the draft changes per ton loaded • Relationship between draft, depth of lower hulls, and freeboard on a semisubmersible • Converting weight of fuel (lb/cu ft) into long tons and relating that to volume taken on
• First, determine the maximum draft allowed if you must still have one foot of freeboard to the lower hulls. How many feet of water can you add from the current draft before you lose that freeboard? • Use the TPI to figure out how many tons correspond to the total draft increase you just found. Remember to convert feet of draft change into inches. • Once you have total tons, consider whether you must adjust for the specific weight of the fuel (54 lb/cu ft) or if the TPI already accounts for the water density you are using.
• Double‑check the geometry: current draft vs. depth of lower hulls vs. required freeboard – write them all in feet and then convert only the change in draft into inches. • Ensure you’re using long tons (2240 lb) when comparing with the answer choices, not short tons. • Verify whether any density correction is needed or if the problem expects you to assume the same density basis used for the TPI.
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