This Small Business Technology Transfer (STTR) Phase II project will advance the development and prototype testing necessary to transition an innovative large scale generating system from concept to commercialization. The underwater energy generation system is based on the naturally occurring phenomenon of vortex induced vibration (VIV). This device harvests hydrokinetic energy via a system of cylinders that oscillate due to water currents at velocities as low as 2-3 knots (water turbines require 5-7 knots). This system captures energy from water currents - unlike hydroelectric power there are no dams or turbines. The proposed research and development includes: (a) Application of Passive Turbulence Control (PTC) to enhance the hydrodynamic effect of VIV and increase hydrokinetic harvested energy for large scale cylinders; (b) Identification of optimal cylinder spacing as a result of using PTC; (c) Installation of a large 4-cylinder module in the St. Clair River in Port Huron, MI; (d) Classification and research of appropriate materials to extend period between maintenance cycles in harsh marine environments.The broader impact/commercial potential of this project is that it taps into a vast new source of clean and renewable energy - water currents as slow as 2 to 3 knots. Currently, there are only pilot devices for harnessing horizontal hydrokinetic energy (currents, tides). All devices considered are conventional propeller/turbines that target speeds around 5-7 knots (only seven locations with these conditions exist in the US). The vast majority of river/ocean currents in the United States are slower than 3 knots. This leaves the vast majority of rivers and bodies of water in the country untapped for power generation. Renewable energy generation is one of today?s most challenging global dilemmas. The energy crisis requires tapping into every source of energy and developing every technology that can generate energy at a competitive cost within the next 50 years. Development of this technology will bolster domestic energy security and mitigate global climate change. There are numerous commercial and military applications from small scale (1-5kW) to large scale (100MW). Applications span from small portable devices, to direct water pumping for irrigation, direct pumping for desalination, off-shore stations, idle ships, coastal naval bases, etc.