Electric Boat Motor Calculator
The electric boat motor calculator estimates the recommended electric motor size (in kilowatts) needed to properly propel your vessel. By factoring in your boat's fully-loaded weight and hull design, it helps you properly size an e-drive conversion and shows the traditional gasoline horsepower (HP) equivalent.
Understanding Electric Boat Conversions
Replacing a gasoline or diesel marine engine with an electric motor requires sizing the drive based on Kilowatts (kW) rather than Horsepower (HP). However, because electric motors generate maximum torque instantly at 0 RPM, you often need less peak power to achieve the same maneuverability and cruising speeds.
Power Rules by Hull Type
- Displacement Hulls (Sailboats): The most efficient vessels for electric propulsion. You generally only need 2 kW per metric ton (approx. 2,200 lbs) of boat weight to reach hull speed.
- Semi-Displacement (Pontoons): Less aerodynamically and hydrodynamically efficient. They require about 3 to 4 kW per metric ton to overcome drag and achieve comfortable cruising speeds.
- Planing Hulls (Speedboats): Highly inefficient for electric systems. Getting a boat "on plane" requires massive amounts of energy to climb over the bow wave. Planing hulls require roughly 1 kW for every 33 lbs of boat weight, meaning a heavy battery bank is required for even short bursts of speed.
Kilowatts (kW) vs. Horsepower (HP)
Mathematically, 1 Kilowatt = 1.34 Horsepower. However, because gas outboards are rated at peak RPMs (which you rarely cruise at) and electric motors are rated at continuous output, the "effective thrust" of an electric motor is much higher. For example, a 3 kW electric outboard like a Torqeedo can easily replace a 5 HP gasoline outboard in real-world performance.