For information on getting licensed as a merchant mariner, see the Coast Guard's "New Mariners" site:
http://www.uscg.mil/stcw/index.htm
You can find information on renewing a U.S. Merchant Mariner credential (Merchant Mariner Document, License, or Certificate of Registry) in the "Renewal Guide" at the same site:
http://www.uscg.mil/stcw/index.htm
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