Electric Boat Association of Australia

The main components for an electric drive system are similar for all electric boats.

	Electric motor and drive train There are many different types of electric motors. The most popular ones for use in boats are permanent magnet DC motors or brushless motors, operating at 12 to 48 Volts, depending on the power required to push the boat through the water. Motors can be mounted inboard and connected to a drive shaft, but there are also pod motors available that can be mounted under the hull of the boat, which gives a great freedom in the lay-out of the boat and eliminates the use of a drive shaft.
	Electric saildrives are also available and there is a wide range of electric outboard motors ranging from very light ‘trolling motors’ to very efficient high power outboards that can be used as main propulsion. A gear reduction is often necessary in order to be able to use a larger and more efficient propeller. This can be achieved by a gear box or transmission, but because of the loss associated with gearing, many electric drives eliminate it by using slow high-torque motors. Generally the highest efficiency is achieved with a large propeller with a high pitch, that turns relatively slowly through the water. This ensures as little energy as possible is wasted. Some modern electric drive systems have an overall efficiency of up to 50%, whereas in comparison a petrol motor has an efficiency of 10% or less.
	Batteries Deep cycle lead-acid batteries are the most cost effective option to power an electric boat. There are various types available such as flooded cell, gel and AGM batteries. The size of the battery bank fitted to an electric boat will determine the range and performance. The battery bank can be recharged using shore power (power from the grid) or they can be recharged using a combination of solar, wind or diesel/petrol (hybrid technology) energy. Most recreational electric boats will operate on a 24, 36 or 48 Volt battery bank with a high Amp-Hour rating, such as 180Ah or higher.
	As an alternative to lead acid batteries, lithium ion batteries can be used to power an electric boat. They are more expensive than lead acid batteries, but they are lighter in weight, have greater energy density, longer life and can be charged faster. Several chemistries of lithium ion batteries are available. In particular lithium manganese or lithium iron phosphate batteries are the recommended types for electric boats since these chemistries are very safe to use and not a potential fire hazard as are some of the other lithium ion chemistries. Lithium ion batteries are also the most eco-friendly batteries available since they do not contain any environmentally damaging chemicals.
	Motor Controller The controller is the ‘communication link’ between the motor and the battery bank. It allows the boat to go forward and reverse. Most modern controllers are high efficiency and are of the ‘pulse-width-modulation’ (PWM) type. Connected to the controller are the throttle and often a display that gives information on the remaining charge in the battery bank and the range at any given speed.
	Charger Electric energy has to be obtained for the battery bank and can be sourced from the grid, solar panels, a wind turbine, a diesel/petrol powered generator or a combination of these. The battery charger regulates the rate at which the batteries are being charged to ensure that they are not under- or overcharged. Most electric boats are fitted with with “smart”, or multi-stage chargers that keep the charging current more constant for faster charging. With these modern switch-mode chargers battery charging takes place in 3 stages: Boost, Absorption, and Float.