Coaming is any vertical surface on a ship designed to deflect or prevent entry of water. It usually refers to a raised section of deck plating around an opening, such as a hatch. Coamings also provide a frame onto which to fit a hatch cover.
The protective metal sheeting or plating protecting against water entry into ventilation shafts in large ships is called a coaming as it suits this purpose.
The term was borrowed by the aviation industry to refer to a low rim around the opening for an unenclosed cockpit.
In addition, it is the vertical surface rising from a hatch, which forestalls the ingress of water and provides a sealing surface for the hatch cover.
Coaming also refers to the raised structure around the cockpit of a kayak.
References
Coaming Wikipedia(Text) CC BY-SA