The eligibility criteria is - at  least 60 % in PCM and 50 % in English in either 10th or 12th std . So you are not eligible to apply for merchant navy .
There is also a medical fitness test for sea service and with eyesight 6/6 with no colour blindness .

• The eligibility for joining merchant navy is finishing class 12 with Physics, Chemistry and Mathematics.
• Candidates have to be unmarried Indian citizens (male or female).
• Normal vision is required but glasses up to plus or minus 2.5 may be allowed.
• Admission is through an entrance followed by a screening test and a main written examination.
• After clearing the test, there is an interview and a medical test.

Hii

If you are from now PCB stream it is not possible for you to get merchant navy as Merchant Navy have eligibility that candidates have to score at least 60% in their mathematics chemistry and physics as you don't have maths Puma not eligible to get admission there.

All the best!!