By happenstance I just found your recent message, buried deep within the Armed Guard / Merchant Marine website message board.
For a complete list of all of the ships in which your father served, you may wish to try to obtain his military service records, which should provide that, along with possibly a great deal of other information. See this page within the Armed Guard website, http://armed-guard.com/searchmil.html, in particular section II.A.1 - Records of Individuals, Military, for instructions on requesting a copy of his records. You will have to contact the National Personnel Records Center in St. Louis, MO, and provide as much identifying information as you have (name, date and place of birth, date and place of death, Social Security Number, military ID number ["serial number"], etc.). You have his serial number, I see, which may be the single most important piece of identifying information. The page has links to all of the information you will need to request his records, including a required form. There will be a charge for researching, photocopying and mailing the records but the Records Center staff will alert you to the cost before beginning work. Once you have his records and if you have any more questions, come back here again and ask away.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website