I used to be a merchant marine officer - captain of a supply boat for the oil fields in the Gulf of Mexico. Big deal.
Go to south Louisiana and apply for a job as a deckhand with one of the companies that supplies boats to the oil companies (my old company is always hiring). For little more than minimum wage, you can spend long periods of time away from land crowded onto a small boat with a bunch of strangers, two at least of which will be yelling and swearing at you because you are screwing up, doing a dirty, dangerous job while hoping you don’t get seasick.
After a couple of years of that shit, you can pay a bunch of money to go to a ‘sea school’ to study for advancement - to Able-bodied Seaman, or Assistant Engineer, or First Mate, or even Captain. (Different lengths of time for all of these, and depends on what size vessel you worked on.) Take the test required by the Coast Guard, and get your new license, make a little more money, eat a little less shit.
BTW, Merchant Marines are licensed, inspected, etc. by the Coast Guard, and overseen by the DOT except in wartime, when they come under the control of the DOD.
My official title was ‘Master, Near Coastal Steam or Motor Vessels of Not More than 100 Gross Tons’. I was also a Grade B Tankerman. Every five years you have to take a ‘refresher’ test and renew your licenses.
Pre-employment drug screening is a requirement, random testing frequent, and once you earn a license of some kind you can get in deep shit for flunking, even during your time off.