Dear Santosh,
The minimum eligibility for courses in nautical science and Marine engineering is 10+2 or an equivalent examination with physics, chemistry and mathematics. He should also pass a medical fitness test for sea service under standard norms and with eyesight 6/6 with no color blindness.
Candidates wishing to enter the navigational and engineering fields of Merchant Navy need to complete a Bachelors degree in Nautical Science or Marine engineering, before they can gain admission to the field.
Please see the following link for the list of institutes:
http://www.infinitecourses.com/MerchantNavy-Maritime-Nautical-institutes.aspx