The operation of cutting a ship down across the middle, and adding a certain portion to her length. This is done by sawing her planks asunder in different parts of her length, on each side of the midship-frame, to prevent her from being weakened too much in one place. One end is then drawn apart to the required distance. An intermediate piece of timber is next added to the keel, and the vacancy filled up. The two parts of the keelson are afterwards united. Finally, the planks of the side are prolonged, so as to unite with each other, and those of the ceiling refitted.