Electric outboard motor

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Electric outboard motors are gaining in popularity and will increase their market share, in part due to improvements in battery storage[1]. Recently developed electric outboards are powered with brushless DC motors located in the power head like a conventional petrol engine. With this setup, the electronics and motor are not immersed like older traditional trolling motors that use an immersed motor directly coupled to the propeller[2]. Another advantage of newer types 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. Modern electric outboards range in size from 220 Watts for types suitable for small boats[3] up to 10 kW to replace a petrol engine of 25 HP or more[4].

Power supply[edit]

The advantages of electric boat propulsion systems are the low maintenance costs, the limited noise, solar recharging, more reliable maneuvering and emission-free operation[5]. 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.

Costs[edit]

After factoring in the cost of batteries, electric outboard motors cost from 30%[6] to 200% more than 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$1,999.00 (2017)[7] 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.[8]

Models[edit]

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

1 HP = 0.745 kW and 1 kW = 1.341 HP[9]. However, petrol engines are rated at the propeller shaft and their propellers are very inefficient in lower speed applications. Electric outboards (except trolling motors) place a great deal of effort on the development of efficiency including the propeller and typically achieve a 2:1 to 3:1 efficiency gain vs gasoline motors[10]. Therefore a smaller electric outboard is equivalent to a larger gasoline outboard by a ratio of 2 to 3[11].

EP Carry[12] For dinghies up to 13 ft and 600 lb displacement.

Input power (W) 220
Propulsive power (W) 132
Max. overall efficiency (%) 47
Typical speeds on boats to 13 ft (Knots) 3.5 to 4.2
Architecture traditional motor on top, drive shaft and bevel gear reduction
Battery type LiFePO4, sealed, buoyant
Battery voltage 24
Battery capacity (Wh) 240
Motor weight (lb) 14
battery weight (lb) 6.4
max, prop speed (RPM) 700

Torqeedo[13] for boats from 1 ton and up[edit]

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

ePropulsion[14][edit]

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

AquaWatt[15][edit]

Green
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)

Elco[16][edit]

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)

Pure Watercraft[17][edit]

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)

KARVIN[18][edit]

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

See also[edit]

References[edit]

  1. ^ "Electric Boats and Ships 2017-2027: IDTechEx". IDTechEx. 2016-12-20. Retrieved 2017-10-19. 
  2. ^ "Electric Paddle". www.epcarry.com. Retrieved 2017-10-19. 
  3. ^ "Electric Paddle". www.electricpaddle.com. Retrieved 2017-10-19. 
  4. ^ "Pure Outboard". Pure Watercraft. Retrieved 2017-10-19. 
  5. ^ "Electric Outboards | Electric Outboard Motors". www.elcomotoryachts.com. Retrieved 2017-10-19. 
  6. ^ "Electric Paddle". www.electricpaddle.com. Retrieved 2017-10-19. 
  7. ^ "Outboard - Travel 1003 - Torqeedo". www.torqeedo.com. Retrieved 2017-10-19. 
  8. ^ "Calculator for electric boat motors". Retrieved 2010-11-11. 
  9. ^ "Power Conversion Online -- EndMemo". www.endmemo.com. Retrieved 2017-10-19. 
  10. ^ "Performance & Efficiency - Torqeedo". www.torqeedo.com. Retrieved 2017-10-19. 
  11. ^ "Performance & Efficiency - Torqeedo". www.torqeedo.com. Retrieved 2017-10-19. 
  12. ^ "Electric Paddle". www.electricpaddle.com. Retrieved 2017-10-19. 
  13. ^ "Torqeedo 2017 catalog" (PDF). 
  14. ^ "ePropulsion 2016 brochure" (PDF). 
  15. ^ "AquaWatt 2016 catalogue" (PDF). 
  16. ^ "Electric Outboards | Electric Outboard Motors". www.elcomotoryachts.com. Retrieved 2017-01-31. 
  17. ^ "Pure Outboard". Pure Watercraft. Retrieved 2017-01-31. 
  18. ^ "KARVIN electric outboard motor". KARVIN MOTORS.