I believe those huge legs provide the buoyancy, while storing some oil.

Then cables go down to huge anchors that work to keep it in position.

Whether it floats OK, unsecured in a Cat 5 hurricane, I have no idea about.

Interesting fact. It was designed for 140 mph winds. :)
[link to www.offshore-technology.com (secure)]

I think it floats on the hulls, plus is connected to the sea floor. And of course the anchor system.

"Tendons / piles
There are 12 tendons, three per corner, each with a 28in-diameter and a wall thickness of 1.2in.

Each tendon is approximately 2,852ft-long and the total weight for the 12 tendons is 6,150t.

The tendons are connected directly to piles in the seafloor. There are 12 piles, each 84in in diameter and 375ft-long, weighing 260t. The piles and tendons were fabricated by Aker Gulf Marine at its yard in Ingleside, Texas, US."