In 1881, the Parisian engineer Gustave Trouvé became the first to navigate using an electrically powered boat. Today, although still not yet standard across all leisure craft, electric propulsion is rapidly gaining prominence within the boating industry.

Environmental protection is not the only advantage of electric propulsion. Electric motors are quiet, compact (excluding battery weight), flexible in installation, and cost-efficient in operation compared with traditional internal combustion engines.

Electric Boat Motors: Advantages Outweigh the Drawbacks

Beyond their minimal environmental impact, electric motors offer several key benefits:

• Silent operation: ideal for onboard comfort and particularly valuable in inland navigation (fishing, leisure cruising), where noise reduction is essential
• Lower operating costs: electricity is significantly cheaper than fossil fuels
• Compact and lightweight design: easier installation and handling compared with diesel engines
• Energy autonomy potential: in sunny climates, solar generation combined with adequate storage can provide near-total independence
• Zero emissions: allowing access to environmentally protected areas
• Ease of use: suitable even for less experienced boaters
• High reliability: fewer starting issues and reduced maintenance requirements

These advantages contribute to significantly lower operating and maintenance costs compared with conventional engines.

Limitations to consider

Despite these strengths, two main constraints remain:

• Higher upfront cost compared with internal combustion engines
• Battery limitations, including cost and relatively restricted range

 

Key Criteria for Selecting an Electric Motor

Choosing the right electric motor requires consideration of several factors:

• Vessel size and weight
• Onboard load
• Battery type and performance
• Navigation environment (freshwater or seawater)
• Intended use and cruising profile

 

Motor Power and Performance

In France, manufacturers typically express motor power using three units:

• Horsepower (hp)
• Kilowatt-hours (kWh)
• Pounds (lbs), representing thrust

Thrust (lbs) reflects propulsion force rather than engine power and is commonly used for electric motors.

The appropriate motor is one whose power is close to that required to propel the vessel at its maximum loaded displacement.

Indicative examples

• A 4-metre boat weighing approximately 400 kg (fully loaded):
  • Minimum thrust: 36 lbs
  • Battery: approx. 70 Ah
• A vessel of approximately 2,000 kg:
  • Motor: 86 lbs thrust (approx. 1.4 hp)
  • Battery: approx. 100 Ah

👉 The key principle is achieving a balanced relationship between motor power and battery capacity, ensuring optimal speed, efficiency and onboard safety.

Operating Environment: Freshwater vs Seawater

Motor selection must account for the navigation environment:

• Freshwater motors: built using corrosion-resistant materials suitable for inland use
• Marine (saltwater) motors: equipped with enhanced anti-corrosion protection

Electric motors used at sea generally require greater power than those used on inland waters, to cope with more demanding conditions.

Note: marine electric motors are often identifiable by their white finish.

Battery Selection: A Critical Component

Battery quality is essential to ensure optimal motor performance and longevity.

Three main battery types are available:

Lead-calcium batteries

• Most affordable and historically widespread
• Limitations:
  • High self-discharge
  • Fewer than 300 charge cycles
  • Limited depth of discharge (<50%)

AGM batteries

• Suitable when combined with appropriate charging systems (solar or wind)
• Advantages:
  • Over 600 cycles
  • Full discharge capability
  • Maintenance-free storage

Lithium batteries

• Over 5,000 charge cycles
• No self-discharge
• High energy density and efficiency

👉 Lithium batteries currently represent the most effective and future-proof solution, despite higher initial cost.

Additional Considerations

• Optimised load matching between motor and propeller shaft ensures maximum propulsion efficiency
• 48V systems:
  • Safer in marine environments
  • Reduce risks associated with high voltage
  • Facilitate installation without advanced electrical expertise

Retrofitting: replacing a combustion engine

When converting from a thermal engine to electric propulsion, the most suitable configuration is typically:

• Saildrive or shaft line systems, which minimise structural modifications

In many cases:

• Existing interfaces can be retained
• Only the saildrive base may require replacement

For experienced DIY users, installation can be relatively straightforward.

Technical note: Saildrive vs Z-drive

• Saildrive: fixed transmission system
• Z-drive: steerable system with articulated transmission

Electric motors offer installation flexibility, often allowing a simplified configuration (L-shape rather than Z-shape), improving efficiency and integration.

Innovative Example: the eJet Tender

At the Cannes Yachting Festival (10 September 2018), the Zodiac Nautic Group introduced the Avon eJet 450, commonly referred to as the eJet Tender.

Developed through collaboration between Avon Marine and Torqeedo—a global leader in electric propulsion—this fully electric tender is specifically designed for integration with large yachts.

Key specifications include:

• Torqeedo Deep Blue motor: 55 kW
• Lithium-ion battery capacity: 30.5 kWh

Thanks to Torqeedo’s Hydrojet technology:

• Top speed: 31 knots
• Range:
  • Approx. 90 minutes at 23 knots
  • Up to 7 hours at 5 knots

A notable advantage is the absence of a reduction gearbox, as jet rotation speeds are fully compatible with electric motor characteristics.

 

Selecting the right electric motor for a boat requires a comprehensive assessment of technical, operational and environmental factors. While initial investment remains higher, electric propulsion offers compelling advantages in terms of efficiency, sustainability and user experience.

As technologies continue to evolve, electric propulsion is set to become a central pillar of modern yachting.