Electric Outboard Motor: History
Please note this is an old version of this entry, which may differ significantly from the current revision.

Electric outboard motors are self contained propulsory units for boats, first invented in 1973 by Morton Ray of Ray Electric Outboards. These are not to be confused with trolling motors, which are not designed as a primary source of power. Most electric outboard motors have 0.5 to 4 kW direct current (DC) electric motors, operated at 12 to 60 volts DC. 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.

  • electric motor
  • asynchronous motor
  • petrol engine

1. History

The first true electric outboard was invented in 1973 by Morton Ray, founder of Ray Electric Outboards.[1] This unit consists of a brushed DC motor in the powerhead, much like a conventional petrol engine. Production of these motors began in 1974, and approximately 99% of all motors sold are still in service.[2] Ray Electric Outboards currently produces electric outboard motors that range from 135 lbs thrust to 270 lbs thrust. They also manufacture boats to accommodate their units. As the desire for clean technology increased and as battery technology developed, new manufacturers emerged. In 2005, German manufacturer Torqeedo started selling portable outboard units in Europe. In 2007 they started selling in the United States. They currently have outboards ranging from 1 hp to 80 hp. Their 80 hp outboard has the motor contained in the powerhead, much like the Ray Electric outboard. With this setup, the electronics and motor are not immersed like with trolling motors that use an immersed motor directly coupled to the propeller.[1] Another advantage of this setup is that gear reductions allow the motor to operate at higher specific speeds increasing energy density while the propeller can operate at lower speeds for efficiency. Motivated by the pollution of petrol engines, Joe Grez set out to build an electric outboard in 2008.[3] He then founded PropEle Electric motors, Inc., currently the producers of the lightest electric outboards available at 14.4bs. This unit does not have the motor immersed in water, similar to the Torqueedo Deep Blue and Ray Electric outboard.

2. Power Supply

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. There are several battery types in use today with various power-to-weight ratios:

  • Lead-acid batteries have low specific energy of 33 to 42 Wh/kg and when quickly discharged, loses 40% of capacity when discharged fully within 1 hour, but they are very cheap.
  • Nickel-cadmium batteries have specific energy of 40 to 60 Wh/kg, but are rarely used today due to environmental concerns and strong memory effect.
  • Nickel-metal hydride batteries have specific energy of 60 to 120 Wh/kg, contain no cadmium or mercury, have relatively low self-discharge and almost no memory effect. They provide compromise between cost and performances.
  • Lithium polymer, Lithium-ion and other newer battery technologies have specific energy of 100 to 265 (or even more) Wh/kg, but at much higher cost per stored Wh.

Charging the batteries with a photovoltaic solar system, wind turbines and towed generators (when traveling under sails or anchored in strong current) 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.

3. Costs

Electric outboard motors cost two to three times the cost of a four-stroke petrol engine, but operation costs are lower. A 1-kilowatt electric outboard motor, including a lithium battery, can be purchased from US$1800.00 (2016) which is already competitive to a 3 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.[4]

4. Models

In the following section an overview and comparison of electric outboard motors.

To compare with petrol engines: 1 HP = 0.745 kW and 1 kW = 1.341 HP.

4.1. Ray Electric Outboard[5]

  Ray System
200 400 500
Input power (W) 2340 3840 5040
Propulsive power (W) 1860 2980 3730
Static thrust (N) 600 870 1200
Average overall efficiency (%)   50.8%  
Battery type  
Battery voltage (V) 36 48 60

4.2. Electric Paddle[6]

  EP Carry
Input power (W) 220
Propulsive power (W) 132
Typical speed on boats 13 ft (Knots) 3.5-4.2
Max. overall efficiency (%) 47
Battery type LiFePO4, sealed, buoyant
Battery voltage (V) 24
Battery capacity (Wh) 240
Motor weight (kg) 6.3
Battery weight (kg) 2.9
Max. prop. speed (rpm) 700

4.3. Torqeedo[7]

  Ultralight Travel Cruise Deep Blue
403 503 1003 1003 C 2.0 4.0 10.0 40 80
Input power (W) 400 500 1000 2000 4000 10000 33000 66000
Propulsive power (W) 180 220 480 1120 2240 5600 16200 32400
Static thrust (N) 147 178 302 511 841 1401    
Max. overall efficiency (%) 45 44 48 56 54
Battery type Build-in External
Battery voltage (V) 29.6 24 48 345
Battery capacity (Wh) 320 915 320 530 915 2685 2x 2685 12800 30500
Motor weight (kg) 4.4 8.9 17.5 18.3 59.8 139
Battery weight (kg) 4.5 6.0 5.0 5.5 6.0 24 2x 24 149 256
Max. prop. speed (rpm) 1200 700 1200 1300 1400 2400

4.4. ePropulsion[8]

  Lagoon Spirit Navy
1.0 3.0 6.0
Input power (W) 300 1000 3000 6000
Propulsive power (W)   500 1650 3300
Static thrust (N) 111 294   1246
Max. overall efficiency (%)   50 55
Battery type Build-in External
Battery voltage (V) 22.2 40.7 48
Battery capacity (Wh) 333 1017 3042 2x 3042
Motor weight (kg) 1.5 9.8 26.8 28.8
Battery weight (kg) 2.5 8.8 31.5 2x 31.5
Max. prop. speed (rpm) 1800 1200 1800 1550

4.5. AquaWatt[9]

Power Racing Thruster Flash
Input power (W) 15500 26000 50000
Propulsive power (W)        
Static thrust (N)        
Max. overall efficiency (%)        
Battery type External
Battery voltage (V) 48 80 144
Battery capacity (Wh)        
Motor weight (kg) 52 63 94 98
Battery weight (kg)        
Max. prop. speed (rpm)        

4.6. Elco[10]

  Electric Propulsion
EP-9.9 EP-14 EP-20
Input power (W) 4800 6240 7920
Propulsive power (W)      
Static thrust (N) 578 907 1068
Max. overall efficiency (%)      
Battery type External
Battery voltage (V) 48
Battery capacity (Wh)      
Motor weight (kg) 29.5 38.6 40.8
Battery weight (kg)      
Max. prop. speed (rpm)      

4.7. Pure Watercraft[11]

  Pure Outboard
Input power (W) 20000
Propulsive power (W)  
Static thrust (N)  
Max. overall efficiency (%)  
Battery type Build-in
Battery voltage (V) 350
Battery capacity (Wh) 6000
Motor weight (kg) 41.7
Battery weight (kg) 42.2
Max. prop. speed (rpm)

4.8. KARVIN [12]

  KARVIN 2700 KARVIN 5500
Amp hour rating. min. 80 Ah battery 120 Ah battery
Battery voltage - 3 in 1 24V/36V/48V 24V/36V/48V
RPM max. 900/1200/1500 900/1200/1500
Comparable petrol outboards in HP (thrust) 9,5 19,5
Min. overall efficiency (%) 85% 85%
Motor type brushless without gear-box => DirectDrive
Power max. kW/HP 2,7 / 3,6 5,5 / 7,4
Torque 27, 5 Nm 43,2 Nm
Static thrust in lbs 210 290
Tensile force [kg] 95 133
Body material aluminium
Propeller material stainless steel
Shaft length Long L (510 mm) / Short S (380 mm)
Continuous regulation Yes
Forward and Reverse Yes
Engine weight 22 kg 26 kg
Electronics Electronic control + Electronic Safety Key + Electronic manual throttle + Immobiliser

The content is sourced from: https://handwiki.org/wiki/Engineering:Electric_outboard_motor


  1. http://www.rayeo.com/index.php/about-us/
  2. http://www.rayeo.com
  3. http://www.electricpaddle.com/about-ep-carry.html
  4. "Calculator for electric boat motors". http://www.all4solar.com.au/ALL4SOLAR_CALCULATOR.htm. Retrieved 2010-11-11. 
  5. "Ray Electric Outboards, Inc. catalog". http://www.rayeo.com/index.php/motors/motor-info/specifications/. 
  6. "EP Carry". https://www.electricpaddle.com/ep-carry-boat-motor.html. 
  7. "Torqeedo 2017 catalog". http://media.torqeedo.com/catalogs/torqeedo-catalog-2017-en.pdf. 
  8. "ePropulsion 2016 brochure". http://www.epropulsion.com/assets/brochure20161104%EF%BC%88zip%EF%BC%89.pdf. 
  9. "AquaWatt 2016 catalogue". http://www.aquawatt.at/data/download/download_1/electric_outboard_1_2016_300_69.pdf. 
  10. "Electric Outboards | Electric Outboard Motors". http://www.elcomotoryachts.com/electric-outboard-motors-2.shtml. 
  11. "Pure Outboard". Pure Watercraft. http://www.purewatercraft.com/portfolio/pure-outboard/#specs. 
  12. "KARVIN electric outboard motor". http://www.karvin.eu. 
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