Bachelors degree is always better than a diploma in any field, for Growth & Promotion.

If you choose a diploma in Nautical Science then you can be a Marine Engineering Instructor, Operations Manager, Training Navigating Officer, Lecturer & Marine Engineer.

so your package will be around 5lacs to 10lacs per annum.

If you do a bachelors degree then Deck Officer, Nautical Surveyor, Scuba Diver, Marine Superintendent.

Packages will range from 8 lacs to 15 Lacs per annum.

I personally suggest you consult a working marine person to get the best advice in today's scenario.