The roll period test is a quick estimation method of ships metacentric height, comperable to a much less rigourous inclining test. Knowing the metacentric height can be used to determine the VCG of the vessel (with knowledge of the vertical centre of bouyancy, a product of the hull form and draught).
The vessel to be tested should be in a sheltered, shallow seaway and free to roll.
The vessel is heeled to one side or the other and released. The time for complete roll cycles are recorded for atleast three complete heelings (repitition will be required, as spurious results are essentially unavoidable).