Electric Boat Motor Calculator

Estimate the continuous electric motor power needed for a boat using its fully-loaded weight and hull type. The result is a preliminary sizing estimate, not a substitute for a full propulsion analysis.

Displacement: Power ≈ Weight (metric tons) × 2 kW
Semi-displacement: Power ≈ Weight (metric tons) × 3.5 kW
Planing: Power ≈ Weight (kg) ÷ 15
These are simplified planning rules. Actual propulsion power depends on speed, hull resistance, propeller, drive efficiency, and operating conditions.
Imperial (lb) Metric (kg)
Include boat, batteries, motor, passengers, gear, fuel and normal operating load.
Typical preliminary estimate: about 2 kW per metric ton.

How This Electric Boat Motor Calculator Works

1. Convert the boat weight to metric tons

The calculator uses the boat's fully-loaded operating weight. Imperial input is converted using 1 kg = 2.20462 lb, then converted to metric tons.

2. Apply a hull-type planning factor

Displacement boats use a simplified 2 kW per metric ton rule. Semi-displacement boats use the midpoint of the stated 3–4 kW per metric ton range, or 3.5 kW per metric ton. The planing option uses the supplied 1 kW per 15 kg rule as a rough estimate only.

3. Convert kW to mechanical horsepower

Mechanical horsepower is calculated as HP = kW × 1.341022. This conversion changes units only; it does not mean an electric motor and combustion engine will produce identical boat performance in every application.

Why the estimate is not a final motor specification

A proper marine propulsion selection should also consider target speed, waterline length, hull resistance, propeller diameter and pitch, gear ratio, motor/controller efficiency, battery voltage, loading, and operating conditions. For displacement boats, required propulsive power rises strongly as speed increases, so a small change in cruising speed can materially change the required motor power.

Source: onlysuperyachts.com/calculators/electric-boat-motor-calculator/