Merchant Mariner's Document
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The Merchant Mariner's Document (MMD), or Z-Card, is issued by the United States Coast Guard in accordance with the STCW guidelines, and is the standard documentation required for all crewmembers of U.S. ships with a Gross Register Tonnage of over 100. An entry-level MMD allows one to work on the deck as an ordinary seamen (OS), in the engine department as a wiper, or in the steward's department. With experience and testing, qualified ratings such as able seaman (AB) or qualified member of the engine department (QMED) can be obtained.