Above The Waterline
In a drilling platform, the moon pool is usually above sea level, and is open to the air above and below. The research vessel Western Flyer (pictured) also has a moon pool above the waterline, which its SWATH (twin-hull) design allows. See part A of the diagram. The chamber above the moon pool is also connected to the open air via stair wells and passages.
Read more about this topic: Moon Pool, Types of Moon Pools and Associated Structures