This is a remnant of a 1970s science project.
By Ken Sakamoto, Star-Bulletin

Let's put ourselves into the mindset of the early 1970s, when politicians actually listened to scholars and scientists instead of fleeing in terror from higher education. The University of Hawaii's marine-science guru Dr. John Craven, under the gun to conjure something spectacular for the 1976 bicentennial, came up with an enormous "floating city," and had it designed by architect Kiyonori Kikutaku.

It would look like a mile-wide water lily, supported by vertical tanks in sequence, similar to those used to support oil-drilling platforms while they're moved into position. Estimates to build this thing ranged up to $200 million, so Craven got a grant for $80,000 to build a scale model.

Some scale model. It was 17 feet tall, made of steel, divided into ten clip-together modules, each of which had three vertical tanks. Even with a budget of $80,000 it took 130 volunteers to construct it. Stories at the time say the whole unit was 150 tons, but don't say whether it was gross weight or displacement.

Tests went well in Kaneohe Bay until an over-zealous tow boat pulled the structure so quickly that water flowed into the flotation tanks, and down she went. Oops. The program never quite recovered from the ridicule, even though the model was refloated a few weeks later. The model was eventually scuttled in shallow water near Coconut Island, where it sits today.

The vertical-submerged-tank concept eventually inspired other craft, such as the U.S. Navy's FLIP ship and the later SWATH boats. As for floating cities, one was eventually built off Hawaii - for the movie "Waterworld." Part of that model sank too.

Craven went into naval intelligence. There's a lesson here somewhere.