See, between these two, the undisputed fact it that if you want to study intensively about ship designing, then Bachelor of Technology in Naval Architecture and Ship Building is the way to go. Almost 90 percent of the core syllabus of both the branches will be same, however the remaining 10 percent is where your interest lies, so if you chose the former, then you'll get more exposure to ship building and you'll learn more insights about the deeper mechanical technologies used to achieve them.

Hope I have answered your question. All the best!