Size your electric boat propulsion system in minutes

A practical rule of thumb is 2–3 kW per tonne of displacement for cruising at 5 kn. A 6-tonne 32-footer typically lands on 12–18 kW continuous; an 11-tonne 40-footer wants 22–28 kW. The wizard sizes this from your real LWL and displacement rather than a rule of thumb.

48 V is simpler and cheaper, fits most consumer marine standards, and is fine up to about 15–20 kW. 96 V halves the DC current at the same power, which makes cable cross-sections, fusing, and bus bars dramatically easier above 20 kW. Above 30 kW, 96 V or higher is the only sensible choice.

Battery sizing follows your runtime requirement — kWh = power × hours ÷ usable depth of discharge. 1.5–2 hours of motoring at cruise speed is the realistic floor for most cruisers, which translates to roughly 1.5× your continuous power figure in kWh of LiFePO4.

DC current is what flows from the battery into the motor controller. Phase RMS is what flows from the controller out to each of the three motor windings. The phase current is typically 1.2–1.5× higher than DC, which matters for sizing the controller's phase output and the motor cabling.

Running the wizard and seeing all results is free. The €29 charge is for the downloadable PDF spec sheet — useful when you want to share the spec with installers or vendors. No signup, no account, no subscription.

Usually yes for shaft-drive boats — the shaft, stuffing box, and stern tube are typically reused. You may want to repitch the propeller because electric motors deliver torque differently than diesels. Saildrive boats need a leg-specific adapter from the motor manufacturer.

All-in budgets vary widely with boat size and DIY vs turnkey. Roughly: small launches €3k–8k, 30 ft sailboats €15k–25k, 35 ft cruisers €20k–35k, 40 ft sailboats €30k–50k. The wizard outputs the technical spec — pricing depends on vendor and installer choices.