Equipment for draining a port

The caption that goes with this drawing reads modo di votare un porto "how to dry up a port", that is how to facilitate the works for building submersed foundations or for deepening the port's bottom. Draining a portion of water helps excavate the depth. The equipment consists of a caisson probably of wood, made up of movable bulkheads mortised into each other, driven into the sea-bed and connected with each other via four quadrangular posts.
Manuscript B, sheet 6 r.