Nothing really of interest in this reef - just a lot of concrete and tire units that have been sinking down into the mud for over twenty years. But someday ...
All manner of concrete, steel, and stone rubble from dredging, demolition projects, and other construction is used as artificial reef materials. This material is generally available at very low cost or free from construction companies who are more than happy to get rid of it. Transportation costs determine where this material is used by the Reef Program.
Portholes are used to let light and air into a ship. They are usually constructed of brass for corrosion resistance, which makes them highly desirable as collector's items. The drawing at right shows all the major parts:
The immovable backing plate, bolted to the vessel's hull, which carries the hinges for the swing plate and deadlight
The glass swing plate, which is secured shut by large butterfly nuts called 'dogs'
The deadlight, used when it is desired to black-out the vessel, as in time of war