Trivia: The most remembered line from "Waterworld," "Dryland is not a myth; I have seen it," is never spoken in the actual movie.
Trivia: Prior to "Titantic" (1997), "Waterworld" was the most expensive movie (at $175 million) ever produced.
Trivia: The land they end up finding at the end of the movie was in fact to be the tip of Mount Everest. I know this because I once saw a copy of the movie where they discovered the plaque left behind by the first climbers of the mountain and it said it was Mount Everest. This was the movie's broadcast premiere on ABC in 1998, and up until recently, the plaque was never shown on-screen again.
Trivia: After repairs in 1990 the Exxon Valdez went back to sea as the Exxon Mediterranean. However, no one would recognize or associate any notoriety to the new name so the old name was kept for the movie.
Trivia: Kevin Reynolds is credited with directing the film, but he left the project early after repeated, frequent clashes with Kevin Costner who disagreed with virtually every cinematic element and ultimately took over the job.
Answer: Most likely to make sure that the Mariner and Helen couldn't follow them and rescue Enola. They were trying to find Dryland and if Enola was taken from them, they'd never be able to find it. Also the smokers ship was filled with people and using the Mariner's boat and constantly going back and forth from Dryland to the ship would have taken too long. Better to use the ship they're all on and get them there quicker. Also, none of the Smokers could read the map that was on Enola's back.