Spread over 26 acres on Long Island’s North Shore, with a private beach, is a tiny but top-ranked college that offers each and every one of its students a full-tuition scholarship for all four years.

Of course, there’s a catch.

At Webb Institute — one of only nine colleges in the country that is completely tuition free — there is just one academic option: a double major in naval architecture and marine engineering.

“When you are applying to Webb, you have to love boats,” said Lauren Carballo, the admissions director.

Thanks to a hefty endowment and devoted alumni, Webb has been able to maintain free tuition even as such promises become increasingly rare. Cooper Union for the Advancement of Science and Art, for example, dialed back its commitment that education be “as free as air and water” and began offering students only half-tuition scholarships in 2014.

“We’re the only engineering school in the country that offers no tuition,” Carballo said. Still, “a lot of people don’t know we exist.”