别处转来的，你看下：
A moon pool is a feature of marine drilling platforms and drillships, some marine research and underwater exploration or research vessels, and underwater habitats, in which it is also known as a wet porch. It is an opening in the floor or base of the hull, platform or chamber giving access to the water below, allowing technicians or researchers to lower tools and instruments into the sea. It provides shelter and protection so that even if the ship is in high seas or surrounded by ice, researchers have the opportunity to work in shirt-sleeved comfort compared to being on a deck exposed to the elements. A moon pool also allows divers or small submersible craft to enter or leave the water easily in a more protected environment.
Moon pools can be used in chambers below sea level, especially for the use of Scuba divers, and their design requires more complex consideration of air and water pressure acting on the moon pool surface.
另外，给你个链接，维基百科上的对于MOON POOL的解释。
http://en.wikipedia.org/wiki/Moon_pool
