This is a re-re-post with updated, working links.
The 1977 film Shock Waves would make a great double feature with Death Ship since they both deal with Nazi inspired supernatural terror on and near the high seas.
First viewed this when it aired on Night Flight in the 1980s. Director Ken Wiederhorn (King Frat, Eyes of a Stranger, Meatballs 2, Return of the Living Dead 2) does a superb job creating tension and terror on a very low budget. Brooke Adams along with horror veterans Peter Cushing and John Carradine are the most notable faces in the film.
They story follows a group of vacationers who charter a boat to tour, fish, and dive around some Caribbean Islands. The weather becomes odd, the boat collides with a mystery freighter, and the hull is damaged. This forces the crew and passengers to seek refuge on a small island where they encounter Peter Cushing's character and things take a terrifying turn for the worse.