How much is the pay I heard the hours are what one month on one month off a lot of guys here in south Florida are heading to Alaska for work but a lot of them have criminal history.Merchant Mariner. You need a TWIC (Transportation Worker Identification Card) and an MMC (Merchant Mariner Credential). For the former they do a background check. You're supposed to have not comited a crime in the last 7 years. A friend of mine had something (not major) and got it. You have to explain the circumstances. You can try getting the TWIC (it might be $120). If you get it, you can pursue the MMC.