Complex sentence: The cable is secured on each end of the river by steel posts and as the ferry crosses the river, the force of the boat, with the help of rollers on the side of the boat, pulls the normally submerged cable out of the water.
Split into simpler sentences: The cable is secured on each side of the river by steel posts. As the ferry crosses the river, the force of the boat, with the help of rollers on the side of the boat, pulls the normally submerged cable out of the water.