hello aspirant,

you can join merchant navy right after you pass your 10+2 exam. you need to be an unmarried indian citizen , you need to have physics, chemistry and mathematics in your 10+2 course. there will be a entrance test by merchant navy, if you carck you will go through a ship training course.

another option yo join in merchant navy is doing diploma in nautical science from reputed institute. however you need to give your 100 percent. however I would suggest you go through the job perspective area of working in merchant navy before joining.