DIY & install
Feb 14, 2026
How many kW does a sailboat need?
Practical sizing guidance for DIY sailors.
sizingsailboatsdiy48v96v
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5-step electric propulsion wizard
Size your electric boat propulsion system in minutes
Enter your boat's dimensions, target speed, and range — get battery kWh, DC & phase currents, and a professional spec sheet ready for any installer or supplier.
Start sizing — it's free
No signup required·Free to run·PDF from €29
1
Boat basics2
Power3
Range4
Charging5
Spec sheetInstant size estimate
Hull type
Power
10 kW
continuous
Battery
32 kWh
666 Ah
Range
~10 nm
@ 5 kn cruise
DC current
347 A
48V bus
Snapped to 10 kW power bucket · tweakable in the wizard
Saves 114 L diesel & 305 kg CO₂/yr at 50 h motored
Full breakdownOpen in wizard with these valuesHeuristic preview · full wizard refines with drive type, range profile & charging
ABYC
E-11 referenced
~10 min
Average time
Free
To run wizard
€29
PDF download
Quick start
Jump in pre-filled for your boat
One click opens the configurator with realistic defaults for your length and hull type — tweak from there.
Free tools
Two ways in — pick the one that fits
Start with the savings calculator if you’re wondering whether electric pays back, or dive into the full configurator if you already want a spec.
Diesel-vs-electric savings
How much do I save going electric?
Three sliders. Get liters of diesel displaced, kg of CO₂ avoided, and lifetime running cost saved over 10 years.
CO₂ & fuelRunning cost30 seconds
Open calculator
Full propulsion configurator
Size battery, current & cabling
5-step wizard. Get battery kWh, DC & phase current, cable cross-section, and a vendor-ready PDF spec sheet.
Battery sizingCable sizingVendor PDF
Start the wizard
What makes it useful
Built for real electric boat projects
Not a generic calculator — every output is tuned for marine propulsion realities.
Boat-specific sizing
Monohull or multihull, shaft drive or saildrive — sized from your real LWL and displacement.
Performance-aware
Speed vs power curve shows how close you are to hull speed and available headroom.
Vendor-ready output
DC current, phase RMS, pack kWh, and Ah — exactly what installers and suppliers need.
Who uses it
Who is this for?
Sailboat owners
Planning a diesel-to-electric repower? Get credible numbers before talking to any installer.
DIY builders
Understand what current, cable size, and battery capacity you actually need before buying.
Boatyards & installers
Conservative continuous ratings and a shareable spec to vendors — installer-friendly defaults.
Hybrid & auxiliary projects
Works for any electric auxiliary or hybrid setup, not just full repowers.
What you get
A vendor-ready spec, backed by the math
Run the wizard free, see every number with its formula, then download a 6-page PDF when you're ready to share with vendors.
In the wizard · free
- Battery voltage, kWh & Ah sizing
- DC and phase current (RMS + peak)
- Power bucket recommendation
- Estimated charging time
- DC voltage drop & cable sizing
- 48V vs 96V bus voltage comparison
- Live formulas alongside every output
In the PDF · €29
Personal cover
Your boat's actual battery, controller, motor and prop numbers on the front page.
Math appendix
Every formula with substituted values — the full derivation behind each output.
Installer checklist
Conservative continuous ratings & a procurement checklist installers can work from.
Sneak peek — what’s inside the PDF
6 pages · A4 PDF
Electric Boat
Propulsion Spec Sheet
Generated · Spec ID · Receipt
Your propulsion system
1. BATTERY
24.0kWh
310 Ah
2. CTRL
142A
77V bus
3. MOTOR
18.0kW
cont.
4. PROP
—
sized
Cover + system
DC Voltage Drop
Cable run
Cross-section
Resistance
Voltage drop
Ampacity
Suggested size
Cabling & protection
Math Appendix
1. Section
─── = ───
2. Section
─── = ───
3. Section
─── = ───
4. Section
─── = ───
Math appendix
Installer Checklist
Installer checklist
Sources & Assumptions
ABYC E-11 · ρ_Cu · k=1.25
Sources & assumptions
Cover above shows example numbers — yours will use your inputs.
Free to run the wizard. Pay only when you download the PDF.
Anatomy of the system
What goes into an electric propulsion system
Every part the wizard sizes for you, in one diagram — from the battery pack to the propeller.
1
Battery pack
LiFePO₄ — sized in kWh + Ah
2
Battery management
Cell balancing, SoC & temperature
3
Motor controller
DC → 3-phase AC inverter
4
Electric motor
Continuous kW + peak rating
5
Shaft & propeller
Pitch matched to cruise speed
6
Onboard charger
AC → DC, sized to shore supply
7
DC bus cabling
Cross-section sized for drop %
Pack sizing
kWh, Ah, and runtime from your DoD and reserve assumptions.
Current sizing
DC continuous, DC peak (10 s / 30 s), and phase RMS + peak.
Cable & voltage drop
Run length, cross-section, and drop % — 48 V and 96 V compared.
Marine-specific formulas
·No signup required
·Vendor-ready PDF
·Conservative continuous ratings
Frequently asked questions
Electric boat propulsion — common questions
Quick answers to what most owners ask before starting an electric repower or new build.
How many kW does a sailboat need for electric propulsion?+
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.
Should I choose 48 V or 96 V?+
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.
How much battery (kWh) do I really need?+
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.
What's the difference between DC current and phase RMS current?+
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.
Is the configurator free? What costs money?+
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.
Will my existing shaft and propeller work?+
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.
What does an electric repower cost end-to-end?+
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.
Fresh from the blog
Latest electric boat guides
New articles on battery sizing, voltage choice, cable runs, and the math behind every spec — updated as we publish.
Regulation
May 25, 2026
ABYC E-30 and the EU electric repower subsidy: what 2026 buyers need to know
A practical guide to the two compliance shifts that change electric repower economics in 2026 — the ABYC E-30 standard for electric propulsion installations and the €40M EU repower subsidy scheme. Eligibility, requirements, retrofit costs, and how the two interact.
regulationrepowersubsidyplanningsafety
Read guide
DIY & install
May 25, 2026
Electric boat repower cost: what to budget in 2026
A realistic breakdown of electric boat repower costs in mid-2026 — motor, battery, controller, charger, installation, compliance with ABYC E-30, and the €40M EU subsidy that changes the net price for many buyers.
costrepowerdiyplanningsubsidy
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Free to run — no account needed
Ready to size your build?
Takes ~10 minutes. Professional output. Pay only for the PDF.