D&D DM Screen: Of Ships and Of Sea - Rules of Play says:

The ocean is a vast and dangerous place, ripe with adventure both above and below the waves. This screen is the perfect accessory for running adventures on the high seas, such as those found in Ghosts of Saltmarsh. The evocative front displays a variety of scenarios your heroes may find themselves in, from a Kraken attack to a meeting with a Sahuagin Baron. On the back, you will find a variety of references to help you in the running of your sea escapades, such as random ships and seafaring hazards.