The basic STI system includes : - drive unit (containing one or two motors) to turn the propeller - controller to operate each motor - bank of twelve batteries to supply 144 VDC to the motors - power distribution busses - shore-power battery charger Batteries are regenerated under sail by the prop spinning in the wake. Hybrid-electric systems also include a DC generator to recharge batteries for long-distance motoring and heavy auxiliary systems use. An optional inverter supplies 120 VAC for onboard appliances.