The Derelict

Publisher's blurb:

This is a short location-based horror adventure where the characters explore a haunted derelict pirate ship in the ocean. The whole adventure can be played in a typical four-hour session. The Derelict is perfect for situations where the party suddenly decides to sail off into a completely new direction and the gamemaster does not have anything prepared for the destination. It is designed to be simple and the gamemaster is empowered to read and run it quickly.

Since combat is not the main focus for this adventure (it is more atmospheric and exploratory), scaling this adventure for parties of different levels is trivially easy.