Sir, i have one doubt. If i choose naval architecture and ocean engg. in IIT madras can i switch to IT jobs later in my career?

It depends on your interset in IT during your education in bechleor programme.
The best example..Mr Sundar Pichai, whio himself from IIT Madras, a B Tech in Metallurgy, he is now CEO of big brand IT firm.
So, have faith on your abilities and interest in IT will post you in desired frame.
Good Luck.