As an ex-Webbie (x'82), there are two things about getting in. First you have to meet the basics, and second you have to pass the interview. The basics are things such as citizenship, age, matrial status, previous GPAs, SAT scores. Anyone in the upper 5% of their highschool class or with a 3.7+ technical college GPA should be able make the basics. The interview is more abstract (at least when I had mine). They are looking to weed people who don't really want to be a Naval Architect or who they think can't or won't apply themselves to the coursework, or those who will not be able to fit into the tight knit student society. You pass or fail at Webb depending on your ability to get along with your classmates because the course load is so heavy. A loner who gets ostracized has a much harder time getting everything done.
Once you get in, it's sink or swim. There is no grading curve, there is very little ability to go back if you get sick or injured (what happened to me). Most of the class weeding occurs in the first two years in the math and marine engineering (i.e. practical math) courses. Even after that you will not be learning how to build boats or yachts, but will be learning Naval Architecture and Marine Engineering, keel to truck, cutwater to dunce cap. Course load is about 150% of a "normal" engineering school and there is no "5-year" option.
If you survive all four years, you will come out kinda warped and twisted (at least all the Webbies I know from my class and others

). When I was there and we did the alumni survey, the next highest professions after NAME were clergy and lawyers in that order. Additionally, do not expect to be handed a job upon graduation. The years of winter work is where you should be lining up up your first job out of school, and how you do during that time will shape your future options.
But in the final analysis, after having work with graduates from all the major NAME/OE schools (Webb, MIT, Michigan, Berkley, Texas, UNO, FAU, FIT, USMMA, USNA, SUNY MAC, Maine Mar, CMA, etc.) a Webb education is probably the most rounded and least limited, with Michigan as distant second. Some schools focus too much on certian "scholastic" subjects and not enough on practical work and applications, making you have to spend two or more years to re-train the person to "real-life" engineering work.
Hope this helps.