Kilowatts to Horsepower: The Power of Electric Boat Motors

When you purchase an electric motor, you will start using a new language to describe the power and performance available.

New words and names will replace what you know – horsepower becomes kilowatts, fuel flow becomes amps, and the gas tank capacity becomes the voltage produced by the battery.

Whereas horsepower is a measure of the energy produced by the motor, electric motors use kilowatts which is a metric that refers to the amount of power consumed by the electric motor.

At a Glance:
1️⃣ To convert kilowatts (kW) to horsepower (hp), you can use the following conversion formula: 1 kilowatt = 1.34102 horsepower

2️⃣ So, to convert kilowatts to horsepower, simply multiply the value in kilowatts by 1.34102.

3️⃣ For example, if you have a 10 kW electric motor, you would multiply 10 by 1.34102, which equals 13.4102 hp.

A gas-powered boat motor’s fuel tank (measured in gallons) becomes the battery capacity measured in amps.

The diameter of the gas pipes connecting the gas tank to the motor becomes the gauge of wiring connecting the battery to the engine.

In this article, I’ll explore the importance of converting kilowatts to horsepower for electric boat motors while also gaining insights into the relationship between thrust and horsepower.

🎓 Understanding Kilowatts And Horsepower

Horsepower is the unit used to measure a gas-powered or diesel engine’s power, whereas Kilowatts is an electric motor’s power rating. Both units are used to measure of boat motor’s power capability. 

Additionally, I’ve linked to this comprehensive guide to electric outboard motors to deepen your understanding of the topic.

Definitions Of Kilowatts And Horsepower 

The definitions of kilowatts and horsepower are explained below.


Horsepower is the energy needed to lift an item weighing 75 kilograms to a height of one meter in one second. (source: Wikipedia).


A watt is the amount of work one joule of energy can perform in one second. In essence, it is the measure of electrical and mechanical power. A kilowatt is equal to 1,000 watts. (source: Wikipedia).

The power of an electric boat motor is calculated by the formula Power (watts) = Work (energy, joule) ÷ Time (seconds.)

The same value can be determined by calculating the known measurements from an electrical system (volts and amps) using Watts = Volts x Amps.

A 1 kW motor will consume 1 kW/h (kilowatt hour) when it is run at full power for 1 hour.

🏇 How Kilowatts And Horsepower Relate To Electric Boat Motors 

The measures of Kilowatts and Horsepower determine how effective the motor is in powering a boat.

With gas-powered engines, the higher the engine’s horsepower, the more significant its effect is on the following.

The weight of the engine increases and affects the boat’s drag coefficient.

  • The bigger engine increases the boat’s thrust, enabling faster acceleration and speed.
  • A bigger engine consumes more gas and so needs a bigger gas tank.
  • The bigger gas tank adds weight to the boat and also affects the boat’s drag.

With marine electric engines, the higher the output (kilowatts) has the following effect on a boat:

  • To achieve full power capability, the motor needs a correctly sized battery.
  • The larger the battery, the heavier it is, which affects the hull’s drag.
  • More batteries will be needed to increase range, increasing the boat’s weight and impacting storage capacity.

Factors That Impact Kilowatts And Horsepower In Electric Boats

Gas-powered boat motors require the correct gas tank size to ensure sufficient range. 

The number and size of the battery(s) selected determines two electric motor performance criteria:

  • The range
  • The kilowatt (power rating) delivered by the motor

Different battery combinations can achieve the desired power rating.

Assuming a 10kW (equivalent to 13.5 hp) electric motor is selected, several battery configurations could be applied.

  • A 50 Volt battery rated at 200 Amps will provide 10 kW’s of power (Watts = 50 volts x 200 amps.)
  • Two 12-volt batteries connected in series would produce 24 volts. Assuming 200 amps of current are supplied, the kW produced would be 10 kWs.

The Differences Between Kilowatts And Horsepower

Most countries have adopted the kilowatt as the standardized measure of an electric motor’s power. 

After the European Community adopted this standard in 2010, horsepower could only be used as a supplementary measure, so they’ve had to convert kilowatts to horsepower.

The official conversion rate that serves as a calculator to convert watts from horsepower is 0.7457 kilowatts per horsepower.

The equivalent kilowatt ratings of engines rated on horsepower are listed below in the conversion table.

Horsepower (HP)Kilowatts (kW)
1 hp0.7457 kW
5 hp3.7285 kW
10 hp7.4570 kW
20 hp14.914 kW
50 hp38.285 kW
75 hp55.928 kW

⚡️ Maximizing Kilowatts In Electric Boat Motors

One of the disadvantages of owning an electric motor is that they are supplied with a rated power, and no modification can be done to the motor itself. Therefore, increasing the electric motor’s maximum power output is impossible by modifying the engine. 

Maintenance And Upkeep To Maintain Optimal Performance

The batteries must be kept in optimum condition. This means they must be kept dry, are never allowed to discharge below the manufacturer’s specifications, and are kept on a trickle charge when not in use.

Upgrading And Modifying Electric Boat Motors 

It is impossible to upgrade an electric motor unit to improve its power. Two solutions apply to enhance the electric boat motors’ performance:

  1. Increase the battery size.
  2. Modify the driver’s and passenger’s behavior.

Increase The Battery Size

Doubling the battery size will provide two benefits. First, if the number of batteries is increased, the following will be achieved:

  • If the batteries are wired in series, which will increase the kilowatt power supply (improve thrust).
  • If the batteries are connected in parallel, it will improve the boat’s range.

Modify The Drivers And Passengers’ Behavior

Two adjustments can be made by adjusting the human behavior on the boat:

  • If the driver accelerates more slowly and resists the urge to travel at high speed, it will notably impact battery capacity.
  • Ensuring the boat does not become a dumping ground for unused equipment will reduce the overall weight and, therefore, the amount of motor power required.

🔑 Key Takeaways

Here’s a wrap-up of the critical points to remember from the article:

1️⃣ Horsepower represents the power produced by an engine, while kilowatts measure the power consumed by the engine.
2️⃣ A single horsepower is the energy needed to lift 75 kilograms by one meter within one second.
3️⃣ A watt is defined as the capacity to perform work using one joule of energy per second.
4️⃣ One horsepower is equivalent to 0.7457 watts.
5️⃣ Enhancing the power of an electric motor can be achieved by installing a larger battery or connecting multiple batteries in a string.

Understanding how an electric boat’s kilowatt consumption influences the design choices made by marine engineers is key. While also considering the significance of thrust in electric motors and how it relates to power consumption.

Keep in mind that as the electric motor requires more power, additional space is needed for the batteries, which can impact the boat’s buoyancy.

If you are in the market for an electric boat, carefully sizing the electric motor and required batteries is essential.

I’m the founder and chief editor here at Kite Ship. The electrification of boating is the most exciting thing to happen to the marine industry in a generation! Welcome, and I hope that we can provide the portal you need to dive into the world of electric propulsion and power.