Hello
There are various courses you can opt for after class XII to join merchant navy. Some of them are

• Bachelors in Marine Engineering
• Naval Architecture and Offshore Engineering
• Petroleum Engineering
• Harbour and Ocean Engineering

You can join these courses after completing class XII with PCM subjects.
The admissions to these courses are based on examination such as JEE Main, IMU CET etc.
Top colleges for this course are

• International Maritime Institute
• Samundra Institute of Maritime Studies
• Coimbatore Marine College
• Hindustan Institute of Maritime Training

Good luck