Your vessel has a forward draft of 26'-11" and an after draft of 29'-07". How many tons of cargo can be loaded before the vessel reaches a mean draft of 28'-06" if the TPI is 69?
• Mean draft and how to calculate it from forward and aft drafts • How TPI (Tons Per Inch immersion) is used to convert a change in mean draft to tons loaded • Careful handling of feet-and-inches to inches conversions before doing the math
• First, find the vessels current mean draft from the given forward and after drafts. How do you average two drafts that are in feet and inches? • Next, determine how many inches of draft increase are allowed between the current mean draft and the limiting mean draft of 28'-06". • Once you know the change in draft in inches, how do you use the TPI value to estimate the total tons of cargo that can be added?
• Be sure both the initial mean draft and the final mean draft are expressed in the same unit (inches or feet-decimal) before subtracting. • Confirm that you are using mean draft change (not just forward or aft change) with the TPI. • After calculating tons, compare your answer with the choices and check for small rounding differences that could change which multiple-choice option is closest.
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