Abstract: A caisson structure facilitating communication between a ship and a quay comprises a displacement unit having ballasting members, and a first housing located at one end of the displacement structure and having sufficient height to reach above high tide water level, even when the displacement unit rests upon the harbor bottom. This housing has a platform, from which a ramp extends at least to a second housing at the opposite end of the displacement unit. The second housing comprises machinery for raising and lowering the adjacent end of the ramp, as this is required to facilitate access to the ship with changing tide water levels.