In order to calculate the TPI of a vessel, for any given draft, it is necessary to divide the area of the waterplane by which of the following?

Correct Answer: Option D — 420

Tons Per Inch (TPI) immersion is derived from the waterplane area. Since one long ton of saltwater occupies approximately 35 cubic feet, and there are 12 inches in a foot, the formula is (Area / 35) / 12, which simplifies to dividing the waterplane area by 420.