the caissons' used under water,look like barges, that have been turn over. a flat bottomed water tight wooden structure.
it would have a opening, with a stair or ladder shaft.

the top would be weighted with rocks, to sink the caisson, and it would come to rest at the bottom of a river or under water place and workers could climb down the shaft into the caisson.

there was some sort of an air lock -- think about it,if you take a glass, turn it up side down, you can sink it bottom end down, and the air will stay in the glass, but if put in a straw, An opening to the surface, the water will rush in,

caisson did have leaks like this too, and workers risked being drowned as well as the bends.


my other obsession