Electric boat motors are very efficient. A modern electric outboard turns roughly 85–90% of the energy drawn from the battery into useful thrust, with only small losses to heat in the motor and controller. A petrol outboard, by comparison, wastes most of its fuel energy as heat and noise and delivers only around 25–30% as propulsion.
That gap is the reason electric works so well on the water despite carrying far less stored energy than a tank of petrol. Almost everything you put in actually moves the boat.
Efficiency is also highest at low and moderate speeds, where the motor operates in its sweet spot. Running flat out pushes it into a less efficient zone and, more importantly, makes the hull itself far harder to push, so most of the range you lose at speed is hull drag, not motor losses.
Because so little energy is wasted, gentle cruising stretches remarkably far. To see how that plays out in distance, read how far an electric boat can go or try the range calculator.