One HP is one HP. Isn't it?

Standardisation of power is nothing new. It goes back to James Watt, who defined horsepower in the 18th century to demonstrate the performance of his steam engine. Since then, it‘s been measured uniformly in HP or, in honour of its inventor, in watts. And with that, everything should be clear, shouldn‘t it?

Not completely. It depends on where and how you measure. The most meaningful performance indicator of a drive system is propulsive power, which indicates the performance actually delivered by the motor to move the boat, taking all losses, including propeller losses, into account. This method has been used in commercial shipping for nearly 100 years.
For petrol and conventional electrical outboard motors the propulsive power is not normally revealed. Instead, less meaningful indicators are used, such as shaft power, input power or even static thrust.

That wouldn’t be so bad if the differences between the various power ratings were minimal. But they aren’t; they’re very large. The propulsive power of a petrol outboard with 4 HP shaft power, for example, is just 1 HP. How can the differences in efficiency levels of different types of motor be measured? We’ll shed some light on them.

Advantage Torqeedo

Our focus on optimising propulsive power and our use of the latest technologies means Torqeedo has the highest overall efficiency on the market. That is, every Torqeedo drive converts its available battery power to propulsive power better than any other outboard. This is very important for electric drives because it means more power and range from limited battery capacity.
Overall efficiency levels of various outboards
Advantage Torqeedo
Torqeedo
Conventional
electric
outboard
Trolling
motor
Petrol
outboard

Advantage Torqeedo

Our focus on optimising propulsive power and our use of the latest technologies means Torqeedo has the highest overall efficiency on the market. That is, every Torqeedo drive converts its available battery power to propulsive power better than any other outboard. This is very important for electric drives because it means more power and range from limited battery capacity.
Overall efficiency levels of various outboards
Advantage Torqeedo
Torqeedo
Conventional
electric
outboard
Trolling
motor
Petrol
outboard

Advantage Torqeedo

Our focus on optimising propulsive power and our use of the latest technologies means Torqeedo has the highest overall efficiency on the market. That is, every Torqeedo drive converts its available battery power to propulsive power better than any other outboard. This is very important for electric drives because it means more power and range from limited battery capacity.
Overall efficiency levels of various outboards
Advantage Torqeedo
Torqeedo
Conventional
electric
outboard
Trolling
motor
Petrol
out-
board
  Torqeedo Cruise 2.0 Conventional electric outboard Petrol outboard 5 HP
Input
power
2,000 W
(2.7 HP)
2,000 W
(2.7 HP)
 
Shaft
power
    3,700 W
(5 HP)
Propulsive
power
1,112 W
(1.5 HP)
660 W
(0.9 HP)
995 W
(1.4 HP)
5 HP equivalent

Comparing the Power of Electric and Petrol Outboards: Torqeedo’s HP Equivalent

Electric motors can achieve the same propulsive power as combustion engines with significantly lower shaft power. The reason lies in the different torque curves of electric motors and petrol engines. While the torque curve of combustion engines features a prominent peak, with maximum torque being available only over a limited engine speed range, electric motors feature a much flatter torque curve with ample torque available at any engine speed.
This characteristic allows them to run substantially higher efficiency propellers – even in lower performance classes – than combustion engines. Propeller efficiencies in the lower horsepower class can vary by a factor of 3 between petrol outboards and Torqeedo electric outboards.

To make the comparison easy for boaters used to shaft power ratings of petrol outboards, we always compare the actual propulsive power of our outboards versus petrol outboards. On the following pages, a Torqeedo outboard specified as a "3 HP equivalent" provides the same propulsive power as a 3 HP petrol outboard – even though its shaft power and input power may be substantially lower.

In the Technical Data section, we provide all information on input power, propulsive power, overall efficiency and comparable petrol outboards for your reference.

  Torqeedo Cruise 2.0 Conventional electric outboard Petrol outboard 5 HP
Input
power
2,000 W
(2.7 HP)
2,000 W
(2.7 HP)
 
Shaft
power
    3,700 W
(5 HP)
Propulsive
power
1,112 W
(1.5 HP)
660 W
(0.9 HP)
995 W
(1.4 HP)
5 HP equivalent
  Torqeedo Cruise 2.0 Conventional electric outboard Petrol outboard 5 HP
Input
power
2,000 W
(2.7 HP)
2,000 W
(2.7 HP)
 
Shaft
power
    3,700 W
(5 HP)
Propulsive
power
1,112 W
(1.5 HP)
660 W
(0.9 HP)
995 W
(1.4 HP)
5 HP equivalent

Drive System and Overall Efficiency


Drive train components Drive train Drive train Drive train Drive train Drive train Drive train
Form of energy

Direct current

Form of energy

Direct current

Form of energy

Alternating current

Form of energy

Rotation

Form of energy

Rotation

Form of energy

Thrust

Form of energy
Power Power Power Power Power Power Power
  Current x voltage

Current drain from battery
Current x voltage

Current at cable
Indication of current x voltage over time Torque on motor shaft x angular velocity of motor shaft Torque on propeller shaft x angular velocity of propeller shaft Power on boat x speed of boat
  Input power

Traditional power rating for electric motors (ignoring all system losses)
      Shaft power

Traditional power rating for combustion engines (ignoring high efficiency losses on the propeller)
Propulsive power

Performance indicator used by Torqeedo in combination with input power resulting in overall efficiency (propulsive power divided by input power)
Drive train components Drive train Drive train Drive train Drive train Drive train Drive train
Form of energy

Direct current

Form of energy

Direct current

Form of energy

Alternating current

Form of energy

Rotation

Form of energy

Rotation

Form of energy

Thrust

Form of energy
Power Power Power Power Power Power Power
  Current x voltage

Current drain from battery
Current x voltage

Current at cable
Indication of current x voltage over time Torque on motor shaft x angular velocity of motor shaft Torque on propeller shaft x angular velocity of propeller shaft Power on boat x speed of boat
  Input power

Traditional power rating for electric motors (ignoring all system losses)
      Shaft power

Traditional power rating for combustion engines (ignoring high efficiency losses on the propeller)
Propulsive power

Performance indicator used by Torqeedo in combination with input power resulting in overall efficiency (propulsive power divided by input power)