A vessel's tropical load line is 6 in. above her summer load line. Her TPI is 127 tons. She will arrive in the summer zone 8 days after departure. She will burn off about 47 tons/day fuel and water consumption is 12 tons/day. How many tons may she load above her summer load line if she loads in the tropical zone?
• TPI (tons per inch immersion) and how to convert inches of draft change into tons of loading • Effect of fuel and water consumption on vessel displacement over a voyage • Difference between tropical and summer load line zones and allowable draft/freeboard
• First, figure out how many tons correspond to the 6 inches between the summer and tropical load lines using TPI. • Next, calculate the total weight of fuel and water the ship will burn before reaching the summer zone. • Combine these ideas: think about the maximum extra load you can put on at the start so that, after burning fuel and water, the ship is not overloaded on the summer load line when entering the summer zone.
• Confirm you multiplied TPI × inches correctly to get the maximum extra tons allowed at the tropical draft at departure. • Check that you used the correct number of days and the sum of fuel and water burned per day to find the total weight lost. • Verify that your final answer represents the additional tons above the summer load line at loading, not the displacement at arrival.
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