I found a web page called "U.S. Merchant Ships, Sailing Vessels, and Fishing Craft Lost from all Causes during World War I" here: http://www.usmm.org/ww1merchant.html

You can request a copy of his service records if you have enough of the necessary information, via the form at this link: http://www.archives.gov/veterans/military-service-records/pr....

Good luck in your search!

Nancy