Hello,

No, you need to have a bachelor's degree to apply for GMAT/CAT exam. The Graduate Management Admission Test is a computer adaptive test for admission to a graduate management program, such as an MBA program. Eligibility Criteria for it is as follows:

ACADEMICS - Candidate must be a graduate from a recognized University.

NATIONALITY - There are NO boundaries to the nationality of a candidate.

AGE LIMIT - Candidate must be 18 years of age.

You can go for B.Sc in Nautical science first. You might get 1 year of relaxation in B.Sc as diploma courses are of 3 years. You will have the sufficient time for the preparation of your GMAT/CAT during B.Sc. Then you can give the exam.