An underwater power generating system includes an underwater power generating device, a closed nacelle and a connecting cable system that is provided with an open passage way extending there along that is sealed at one end to the interior of the closed nacelle. The cable system can be used in a number of ways, such as by having the second end being sealed, to prevent air from escaping the closed nacelle, or by having the second end connected to a source of positive pressure thereby permitting the cable to be sufficiently pressurized to provide a positive pressure internally within the closed nacelle that is at least slightly greater than the nacelle at depth pressure, and thus greater than water pressure acting on the exterior of the closed nacelle, to prevent water ingress within the nacelle, as well as to transmit power and/or other data between the nacelle and shore monitoring and control facilities.