The correct answer is D) lowers the center of gravity. Jettisoning weight from the topside of a vessel, such as cargo or equipment, lowers the center of gravity of the vessel. This is because the weight being removed is located above the vessel's waterline, so its removal reduces the overall weight and lowers the vessel's center of gravity. Lowering the center of gravity improves the vessel's stability and reduces the risk of capsizing. The other options are incorrect because they do not directly describe the effect of jettisoning topside weight. Option A does not accurately describe the effect, option B is incorrect as jettisoning topside weight does not reduce the free surface effect, and option C is incorrect as jettisoning topside weight would raise, not raise, the center of buoyancy.