Death Under Sail(1977)

Original title: Nāve zem buras

Successful oncologist Dr. Roger Mills invites a group of friends aboard his yacht for a relaxing getaway. Days later, on a bright sunny morning, he is found dead, shot through the heart. As suspicion falls on those closest to him, local police sergeant Beryl and Mr. Finbow begin a murder investigation that will expose the secrets hidden beneath the carefree voyage.