Question 4746 Deck General

The correct answer is B) GM. Decreasing the riser tension on a semisubmersible drilling unit will decrease the unit's metacentric height (GM), which is a measure of a vessel's stability. As the riser tension decreases, the unit's overall stability is reduced, as indicated by the lower GM value. The other options are not directly impacted by changes in riser tension - free surface moments (A) are related to the free surface effect of liquids on board, KM (C) is the distance from the keel to the metacenter, and KG (D) is the distance from the keel to the center of gravity. Therefore, B) GM is the correct answer based on the relationship between riser tension and a semisubmersible's stability.