163. On a vessel of 12,500 tons displacement, compute the reduction in metacentric height due to free surface in a hold having free water on the tank top. The hold is 35 feet long and 50 feet wide. What is the reduction in metacentric height?

The reduction in metacentric height due to free surface in a rectangular hold is calculated using the formula GG_f = (L * B3) / (420 * Δ), where L is length, B is breadth, and Δ is displacement. With a length of 35 feet, a breadth of 50 feet, and a displacement of 12,500 long tons, this yields a reduction of approximately 0.83 feet.