Electric outboard motors are an option for boat

Boat

A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

 propulsion. Most electric outboard motors have 0.5 to 4 KW DC

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 electric motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s, operated at 12 to 60 volts DC. These systems have the propeller

Propeller

A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...

 fixed directly to the motor which is mounted in the lower unit under water - see trolling motor

Trolling motor

thumb|250px|A 12 volt electric trolling motor mounted on a 8 foot [[inflatable boat]]A trolling motor is a marine propulsion system consisting of a self-contained unit that includes an electric motor, propeller and controls, and is affixed to an angler's boat, either at the bow or stern...

. This setup limits the power output. Recently developed outboard motors are powered with an AC

Alternating current

In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

 or DC electric motor in the power head like a conventional petrol engine

Petrol engine

A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....

. With this setup a motor can produce 10 KW output or more and is able to replace a petrol engine of 4-8 HP.

Power supply

The advantage of electric boat propulsion systems are the low maintenance costs, the limited noise and emission free operation. The disadvantage is the limited range due to the wieght and size of the batteries. lead acid batteries have high weight (38 watt hours / kilogram) and limited capacity when quickly discharged (60% at 1 hour). Newer battery technologies like lithium systems (e.g. LiFePO4 or Lithium polymer) offer up to seven times the performance of a lead acid battery but they are very expensive. Charging the batteries with a photovoltaic solar system can make the system independent of any external energy source. For longer trips, the system can have a range extending gasoline

Petrol engine

A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....

 or diesel generator

Diesel generator

A diesel generator is the combination of a diesel engine with an electrical generator to generate electrical energy....

 which recharges the batteries.

Costs

Electric outboatd motors cost two to three times the cost of a four stroke petrol engine

Petrol engine

A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....

, but operation costs are lower. A 2 horsepower

Horsepower

Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

 electric outboard motor including a lead acid battery can be purchased from USD 750.00 (2010) which is already competitive to a 2.5 HP petrol engine.