A turbine assembly having: a support structure 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 , the first turbine system having a centre of mass and being pivotally connected to the support structure so that the first turbine system is rotatable, relative to the support structure , 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 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 , the first turbine system having a centre of mass and being pivotally connected to the support structure so that the first turbine system is rotatable, relative to the support structure , 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 . <EOS>