A gentleman-pirate referred to as Doctor Boogie took some video and pictures and this is one of his:
Ruins now, but they must have been GLORIOUS in their prime.
This is the perfect concept for post-Necropalypse housing preparations. At sea is fine, but the same design can used on land.
And here is a video when one of the fort complexes was active:
I think I'd want some more shading awnings for the summer months.
Here's the plan. You and your survival team purchase 100 acres of remote land, or secure rights to build offshore in something like Pamlico Sound, the Chesapeake, or Delaware Bays, Lake Pontchartrain... that sort of thing. I'd say the Great Lakes, too, but hardening against ice may be too expensive. I'd recommend just on shore in that area, so you can have access to the water relatively easily. Then construct one of these per family unit. 4000 each square feet would be fine. You interconnect them with suspended walkways, but set up so that in an emergency you can temporarily cutoff an infected unit from the others.
Solar panels and windmills could be used for power. With a steel skin they are hardened against light arms fire, and with a good foundation you can survive hurricanes. Sniping undead is a simple manner. The stand pipes could have a hollow cavity for a securable tunnel down to an underground bunker (for nuclear threats in case the zombie threat doesn't pan out), where appropriate, or as your drill access to artesian well water. Rain catches on the roof can help feed cisterns for your green houses. That's shelter, food, water, power, and defense in almost unlimited quantities. (Be sure to have a citrus tree or 2. They fruit even when small and no one wants to see me after I'm ravaged with scurvy.) Food is always a weakness, and I can't think of an easy fuel access. A pipe to underground tanks wouldn't last that long. Coal or wood burning stocks even less so. But that's going to be a problem in any situation. You're just gonna have to risk armed wood collection parties on the ground and maybe plant potatoes on a few surrounding acres.
Initial investment... 3 million dollars, each. Who's with me? I figure 9 of em would be good.