He served on individual ships for various shipping companies. He may not have a "Service Record" like a member of the Military that keeps track of all assignments. There are Crew and Passenger Lists at the NARA. Some Book form and some Microfilm. A LDS Family History Center may also have them.
The subscription genealogy site I use, Ancestry.com, has some transcribed and images of pages online of Crew lists. Doing a quick search I see he has 22 entries listed in "California Passenger and Crew Lists, 1882-1957". 8 entries in "Honolulu, Hawaii, Passenger and Crew Lists, 1900-1959". 5 entries "Seattle Passenger and Crew Lists, 1882-1957". 1 entry "New York Passenger Lists, 1820-1957".
He started sailing "in service" about March 1944 (arrived Sept 1944 on USS Mission Capistrano to Hawaii from Marshall Islands. Sailed from San Francisco CA. June 14, 1944, stated "in service" 7 mos.) Of all the entries I found the last seems to be dated 1958 which is about the time limit of the databases online. There might be more for him on other crew lists yet to be transcribed for online access.
See if your local Library has Ancestry or local LDS Family History Center or subscribe yourself.
This should also help you:http://www.usmm.org/index.html#anchor252856