Your vessel has a displacement of 24,500 tons. It is 529 feet long and has a beam of 71 feet. You have timed your vessel's rolling period to be 25.0 seconds. What is your vessel's approximate GM?
• Use the rolling period formula that relates GM to the roll period and beam • Remember that a longer rolling period generally means a smaller GM (softer, slower roll) • Keep track of units: feet for dimensions and seconds for time
• What standard formula do we use on exams to estimate GM from the observed rolling period and beam? Write that down first. • After plugging in the roll period and beam, are you taking the square of the period or the beam anywhere in the formula? Double‑check that step. • Once you calculate a numerical GM, which choice is closest to your computed value?
• Be sure you are using the version of the formula for a ship in salt water, not fresh water. • Confirm that the beam in feet (not meters) and period in seconds are correctly substituted before doing arithmetic. • After you compute GM, ask: Does the value make sense? A very small GM gives an extremely slow, easy roll; a very large GM gives a quick, snappy roll. Compare this with a 25‑second period.
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