Complex sentence: The line is tied to the stern, but the shark drags the boat backwards, swamping the deck and flooding the engine compartment, forcing Quint to sever the line to prevent the transom from being pulled out.
Split into simpler sentences: The line is tied to the stern, but the shark drags the boat backwards, swamping the deck and flooding the engine compartment. Quint severs the line to prevent the transom from being pulled out.