The bottom two pics are also oil rigs, more specifically, Jackup rigs. The three legs are lowered to the ocean floor and it stands on those. The other ones are tension-leg platforms, they float and are held in place by tensioned cables.
In that case, How many ship-shipping shipping ships could a ship-shipping ship ship, if a ship-shipping shipping ship could ship ship-shipping shipping ships?
Yo dawg, I heard you like ships, so I put a ship on your ship on your ship on your ship, so you can ship stuff while you ship stuff while you ship stuff while you ship stuff!
http://m.funsubstance.com/fun/170167/for-all-you-fandoms-out-there-on-funsubstance/