What is the main conflict in Strata by Terry Pratchett?

When the expedition arrives at the flat planet, they are amazed to see that Jago's claims are true. Before they can land, however, they are hit by a boat attempting to sail the waterfall at the planet's edge. This accident disables the ship and leaves the three explorers without a way to return home. The accident represents the main conflict of the story, as the main characters will now spend the rest of the book attempting to find a way off the planet.