What are "limber holes and limber chains"?
Thanks Frank for your great answer (below).
The only thing that I would change, is that the limber holes would be through the frames along both sides of the keel (the lowest point where the water would lay) as opposed to the area between the garboard and the start of the turn of the bilge that I would describe as the chine.
I will accept your explanation of the light. It makes good sense.