Constructing a pontoon bridge.To construct a pontoon bridge the first boat launched was rowed up-stream a short distance. The anchor was let go. Its rope was then paid out sufficiently to drop the boat down into position. A second anchor was dropped a short distance down-stream, if the current proved irregular. The second boat was placed in position by the same process. Then the sills of the bridge, called “balk,” could be placed across by floating the second boat alongside the first, placing the ends of the balk, usually five in number, across the gunwale, and then shoving the boat into position by pushing on the inner ends of the balk. These ends had heavy cleats so that they could be engaged over the further gunwale of each boat. The third boat was then placed in position by repeating the process. Then the “chess” layers commenced. The “chess” were the boards forming the flooring of the bridge. After the floor was laid the side rails, visible on the top of the flooring, were laid, and lashed to the balk through slits which were left between the boards for that purpose. This stiffened the whole structure and held the floor in place. Usually an up-stream anchor was necessary on every boat, and a down-stream anchor on every second or third. The floor of the bridge was usually covered with earth or straw to deaden the sound and preserve the chess. In these two photographs the engineers are just completing a bridge across the James.