1. IN A GRAVING DOCK HAVING A GENERALLY CONTINUOUS, BOTTOM-ENCLOSING FLOOR SITUATED ON BEARING SOIL OR THE LIKE AT A DEPTH WHICH IS BELOW THE NATURAL WATER LEVEL IN SUCH SOIL, THE IMPROVEMENT COMPRISING MEANS FOR REDUCING EXCESS NATURAL HYDROSTATIC PRESSURE AS WOULD OTHERWISE BE DIRECTED UPWARDLY AGAINST THE UNDERSIDE OF SAID FLOOR, SAID MEANS COMPRISING DRAINAGE MEANS FOR REMOVING ACCUMULATING WATER FROM BELOW SAID FLOOR INCLUDING PUMP MEANS, A SEEPAGE BED OF MATERIAL DISPOSED UNDERNEATH SUBSTANTIALLY THE ENTIRE AREA OF SAID FLOOR, CONDUIT MEANS INCLUDING PORTIONS SUBSTANTIALLY ADJACENT THE UNDERSIDE OF SAID FLOOR AND COMMUNICATING WITH SAID SEEPAGE BED TO ADMIT ENTRY OF ACCUMULATING WATER FROM THE LATTER, AT LEAST SAID CONDUIT PORTIONS BEING DISPOSED IN DIRECTION WHICH IS GENERALLY PARALLEL TO THE GENERAL PLANE OF SAID FLOOR AND SAID CONDUIT MEANS BEING ADAPTED TO CONDUCT SAID ACCUMULATING WATER TO SAID PUMP MEANS AT A RATE WHICH IS AT LEAST EQUAL TO THAT AT WHICH SUCH WATER NATURALLY ACCUMULATES UNDER SAID FLOOR, AND MEANS DEFINING OPEN VENT PASSAGES BETWEEN SAID SEEPAGE BED AND THE ATMOSPHERE, SAID DRAINAGE MEANS BEING DISPOSED TO REMOVE SAID ACCUMULATING WATER AT A FLOW LEVEL WHEREBY SUCH NATURAL HYDROSTATIC PRESSURE EXCESS IS MAINTAINED AT NEGLIGIBLE VALUE AT THE LEVEL OF THE UNDERSIDE OF SAID FLOOR.