Hello Candidate,
The eligibility criteria for joining merchant navy is finishing class 12 with Physics, Chemistry and Mathematics from a recognised board.

To join in merchant navy you need to have completed +2. If you have completed +2 or equivalent course such as Diploma then you can join in as a Deck Cadet. You will be undergoing basic pre-sea training which will be arranged by the company in which you join.
So yes you can apply.
All the best :)