Merchant Mariner's Document

Under the Seafarers' Identity Documents Convention, 1958, countries with a Merchant Navy or Merchant Marine require identifying credentials for their mariners. The Merchant Mariner's Document (MMD) or Z-card in the United States, and the Ordinary Seaman's Certificate in the United Kingdom are examples of these credentials.

An Ordinary Seaman Certificate is a required certification to obtain a job as an Ordinary Seaman, a rating in a merchant ship's deck department. It consists mostly of proof of identity, proof of some minimal health (possibly including a drug test) and some minimal age, and the standards defined under Standards of Training, Certification and Watchkeeping for Seafarers (STCW). A Z-CARD is also a folded leaflet format, typically used for marketing communications.

The Merchant Mariner's Document (MMD), previously called a Z-Card, is a kind of Merchant Mariner Credential previously issued by the United States Coast Guard in accordance with the STCW guidelines, and, until completely phased out, remains one of the standard documents required for all crewmembers of U.S. ships with a Gross Register Tonnage of over 100. An entry-level MMD allows a mariner to work on the deck as an Ordinary Seaman (OS), in the engine department as a Wiper, or in the steward's department as a Food Handler (FH). With experience and testing, qualified ratings such as Able Seaman (AB) or Qualified Member of the Engine Department (QMED) can be obtained.

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