A turbine assembly having: a support structure (224, 226, 228, 230, 232, 234) comprising first and second buoyancy devices at opposing ends of the assembly and plurality of trusses spanning a width of the assembly and connecting the first buoyancy device to the second buoyancy device; and a first turbine system, supported by the support structure (224, 226, 228, 230, 232, 234), the first turbine system having a centre of mass and being pivotally connected to the support structure (224, 226, 228, 230, 232, 234) so that the first turbine system is rotatable, relative to the support structure (224, 226, 228, 230, 232, 234), about a centre of rotation; wherein the first turbine system includes: a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and a second flowing-water driveable turbine for generating power from water flow, the second turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the operational axes of the first and second turbines are parallel with one another; wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine; and wherein the first turbine system includes a beam connecting the first turbine and the second turbine; and wherein the first turbine is mounted on one surface of the beam, and the second turbine is mounted on a second, opposing surface of the beam. a support structure (224, 226, 228, 230, 232, 234) comprising first and second buoyancy devices at opposing ends of the assembly and plurality of trusses spanning a width of the assembly and connecting the first buoyancy device to the second buoyancy device; and a first turbine system, supported by the support structure (224, 226, 228, 230, 232, 234), the first turbine system having a centre of mass and being pivotally connected to the support structure (224, 226, 228, 230, 232, 234) so that the first turbine system is rotatable, relative to the support structure (224, 226, 228, 230, 232, 234), about a centre of rotation; wherein the first turbine system includes: a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and a second flowing-water driveable turbine for generating power from water flow, the second turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the operational axes of the first and second turbines are parallel with one another; wherein a first flowing-water driveable turbine for generating power from water flow, the first turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and a second flowing-water driveable turbine for generating power from water flow, the second turbine having an operational axis, and being designed for optimum power output when local water flow is aligned with the operational axis; and wherein the operational axes of the first and second turbines are parallel with one another; wherein the centre of rotation is spaced away from the centre of mass of the first turbine system in a direction parallel to the operational axis of the turbine; and wherein the first turbine system includes a beam connecting the first turbine and the second turbine; and wherein the first turbine is mounted on one surface of the beam, and the second turbine is mounted on a second, opposing surface of the beam.