Electric outboard motor
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Electric outboard motors are an option for boat propulsion. Most electric outboard motors have 0.5 to 4 kW direct current (DC) electric motors, operated at 12 to 60 volts DC. These systems have the propeller fixed directly to the motor, which is mounted in the lower unit under water – see trolling motor. This setup limits the power output. Recently developed outboard motors are powered with an alternating current (AC) or DC electric motor in the power head like a conventional petrol engine. With this setup, a motor can produce 10 kW output or more and is able to replace a petrol engine of 15 HP or more. The advantage of the induction or asynchronous motor is the power transfer to the rotor by means of electromagnetic induction. As these engines do not use permanent magnets, they require less maintenance and develop more torque at lower RPM.
The advantages 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 weight 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.[clarification needed] 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 or diesel generator which recharges the batteries.
Electric outboard motors cost two to three times the cost of a four stroke petrol engine, but operation costs are lower. A 2 horsepower 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. Electric motors are usually much more efficient in power to weight ratios. Generally 17.0 pounds of thrust equals 1 HP, however one requires at least twice as much power to compensate for added weight. 
- "Calculator for electric boat motors". Retrieved 2010-11-11.