Question 4738 Deck General

The correct answer is D) increase tank free surface. Increasing the tank free surface on a semisubmersible rig will increase the period of roll while under tow. This is because the free surface effect increases the metacentric height (GM) of the rig, which in turn increases the natural period of roll. Reducing the free surface by plugging vents or dumping tanks would have the opposite effect, decreasing the roll period. Heading into the waves (option C) can also influence the roll period, but this is a separate factor from the free surface effect.