Read it through once

Think how handy this ballast is. The ship leaves port with the lakes all full. As she lightens forward, through consumption of coal, she loses trim—her head rises, her stern sinks down. Then they spill one of the sternward lakes into the sea, and the trim is restored. This can be repeated right along as occasion may require. Also, a lake at one end of the ship can be moved to the other end by pipes and steam pumps. When the sailor changed the slat-frame to-day, he was posting a transference of that kind. The seas had been increasing, and the vessel’s head needed more weighting, to keep it from rising on the waves instead of ploughing through them; therefore, twenty-five tons of water had been transferred to the bow from a lake situated well towards the stern.