NOVELTY - The system has a tapered male engagement pin (49) provided on one of upper or lower modules. A corresponding socket (44) is provided on the other module. The pin comprises a partially tapered end to facilitate alignment of the former module toward a support axis when the pin and the socket are engaged. A flanged lifting collar (24) is provided on the former module, and includes lower and upper bearing surfaces angled with respect to the axis, where upper and lower bearing surfaces contact with each other by rotating an upper collar into a final angular orientation around the axis.    USE - System for aligning and engaging upper and lower modules of an underwater turbine (claimed) i.e. tidal turbine, on a water bed i.e. seabed, along a vertical support axis.    ADVANTAGE - The system provides a generator at a bottom of an underwater turbine, so that center of gravity of the underwater turbine can be lowered significantly, thus improving stability of the underwater turbine in water and reducing amount of material required during construction. The system allows angle of engagement surfaces to be changed to provide a greater or lesser degree of dampening against over-yawing. The system allows a hydrodynamic cowl to be provided around a shock absorber so as to reduce turbulence created in the water flow over the shock absorber, thus reducing damage or interferes with the underwater turbine and attached structure. The system ensures the base structure of the underwater turbine to be anchored securely to the waterbed once installed. The underwater turbine rotates around the support axis so as to maintain alignment with prevailing water current and maintain sufficient support for the system.    DETAILED DESCRIPTION - The system allows a membrane made of a thin non-ferrous sheet. INDEPENDENT CLAIMS are also included for the following:    (1) a method for aligning and engaging upper and lower modules of an underwater turbine along a vertical support axis    (2) an underwater turbine structure    (3) a method for installing an underwater turbine structure on a water bed    (4) an underwater turbine module bearing arrangement    (5) a method for retrieving an underwater turbine installed on a water bed    (6) a deployable buoy and hoist arrangement for retrieving an underwater turbine installed on a waterbed    (7) an underwater turbine    (8) a magnetic coupling.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a structure illustrating a method for installing an underwater turbine structure on a water bed.    Collar (24)    Tail cone (32)    Corresponding socket (44)    Tapered male engagement pin (49)    Water surface (105)