The propulsion system of an Electric boat in its entirety consists of an energy source, an electrical control device, a motor and a propeller.
Most electric boats use lead acid batteries as a source of stored electrical energy.
These batteries many be sealed or open and except for hybrid systems and very large electric boats this energy source is a given. Control systems many be stepped resistors, battery switching or Pulse Width Modulated. By far the most efficient, considering battery life as well as performance, is the Pulse Width Modulated speed controller. Propellers are usually chosen for considerations such as draft, the space available for the swing of the blades and in many cases availability. The electric motor is the item which converts the battery's stored energy into push at the propeller via the speed controller.