1. APPARATUS FOR AT A SITE UNDER A BODY OF WATER COMPRISING A PERMANENT BASE MEMBER FIXEDLY MOUNTED UNDER A BODY OF WATER, SAID PERMANENT BASE MEMBER INCLUDING A PORTION FOR SEATING A WORKING BASE, A COLLAR HAVING A RADIALLY EXTENDING FLANGE FIXEDLY MOUNTED ON SAID PERMANENT BASE, A WORKING BASE MEMBER FOR SEATING ON SAID PERMANENT BASE, GUIDEPOST MEANS FIXEDLY CONNECTED ON SAID WORKING BASE AND EXTENDING IN PERPENDICULAR RELATIONSHIP THEREFROM, LUG MEANS CONNECTED ON SAID WORKING BASE FOR ENGAGING THE UNDERSURFACE OF SAID FLANGE, ACTUATING MEANS IN SAID WORKING BASE FOR EXTENDING AND RETRACTING SAID LUG MEANS TO SELECTIVELY ENGAGE AND DISENGAGE SAID FLANGE, SURFACE-CONTROLLED OPERATING MEANS FOR OPERATING SAID ACTUATING MEANS, A PILOT POST FIXEDLY CONNECTED TO SAID PERMANENT BASE AND EXTENDING IN A SUBSTANTIALLY PERPENDICULAR RELATIONSHIP THEREFROM AND A PILOT LINE CONNECTED TO THE TOP OF SAID PILOT POST, SAID PILOT LINE BEING ENGAGEMEABLE WITH SAID WORKING BASE TO ASSIST IN GUIDING SAID WORKING BASE INTO CONTACT WITH SAID PILOT POST AND ONTO SAID PERMANENT BASE.