The American Merchant Marine at War site (http://www.usmm.org
) is an excellent resource, and includes links to the appropriate government agencies. It's the first place I'd suggest to anyone seeking information.
You can also search the 1930 Census of Merchant Seamen (here on Ancestry at http://search.ancestry.com/search/db.aspx?dbid=8851
) if you know he was a Mariner during 1930.
[Edited]One more thing - Hawaii wasn't a state at the time he enlisted; do you have any additional information?