When I was in Eureka I stopped in at the TSA office and got the TWIC & MMC. These two, other than pro certs., are pretty much all you need to get work on merchant ships. Like any other trade, the more pro certs you have the easier it is to get hired. But get these then hang around in Long Beach or NYC and see what happens!
https://www.uscg.mil/nmc/twic/
https://www.uscg.mil/nmc/credentials/
https://www.uscg.mil/nmc/twic/
https://www.uscg.mil/nmc/credentials/