Ocean energy essentially is either kinetic or thermal, but those forms of energy can be tapped in various ways.
The Roosevelt Island project uses tidal in-stream energy conversion, or TISEC. It generates electricity with a turbine generator driven by the kinetic energy of ebbing and flowing tides. Ideal conditions for TISEC are currents running between 3.6 and 4.9 knots. The density of the water flow means that a TISEC turbine of a given diameter can generate as much energy as a wind turbine four times as large. TISEC currently is one of the two most common types of ocean energy conversion.