House-bank power that keeps up with the way you cruise.
Powerboats run hard — refrigeration, air-con, electronics. Wattonomy sizes your house bank, inverter and solar to what you actually use, turns your engines’ charging into usable power, and specs the fused, code-referenced wiring to match.
A real Wattonomy output — a motor-yacht house bank
System
12 V
Battery
15.36 kWh
Solar
2000 W
Inverter
MP-II 12/3000 12
SmartSolar 150/1002×
200W solar panel10×
Battery → inverter cable7×
Battery → inverter fuse1×
Wire & fuse sizes follow ABYC E-11 — each conductor carries its fuse and stays under a 3% voltage drop.
Built to ABYC & ISO standards
Gauge · fuse · volt-drop sized
Every spec sourced
No house bank, no comfort aboard.
Air-con, refrigeration and electronics drain a bank fast at anchor — and an under-fused lithium bank is a real fault risk. Wattonomy sizes to ABYC E-11 and ISO 13297, puts an AIC-rated Class-T fuse on the bank, and shows the math a surveyor or insurer will respect.
What a powerboat must get right
Bigger loads and constant engine time change the math — here is where it counts.
House bank
Sized to hours of air-con and refrigeration at anchor on an honest depth-of-discharge, kept separate from the engine-start battery.
Capture the engines
You motor most of the time — an alternator and DC-DC charger turn that running time into a charged bank, on top of solar.
Class-T fusing & AIC
Lithium banks can deliver enormous fault current; the main protection and AIC are sized to ABYC 11.10, not guesswork.
Sized, tinned wiring
Every run gauged for ampacity and voltage drop in a marine environment, to ABYC E-11 / ISO 13297.
What you walk away with — free
A house-bank and solar design sized to your real loads
Alternator / DC-DC charging worked into the plan — it adds on top, it never shrinks the bank
A wiring diagram with Class-T fusing and tinned-cable gauges
A parts list you can take to a chandlery or surveyor
Building it for real? Unlock the build binder.
Free gets you a safe, correctly-sized design. The build binder gets you the documents to build it right — and prove it's right.
Printable wiring diagram, yours to keep & tape inside the boat
Full parts list, every line sourced
The volt-drop & fusing calculation trail — the "why" behind every spec
The build binder is a one-time unlock — no subscription, no auto-renew.
Questions
Does it handle alternator and shore-power charging?
Yes — alternator plus DC-DC and shore power are balanced with solar so the bank actually recharges the way you run the boat. Charging never shrinks the battery you carry; it adds on top.
Is the wiring to ABYC?
Every cable, fuse and AIC figure is sized against ABYC E-11 and ISO 13297 and shown with the standard it follows, so you or your surveyor can check the reasoning. It is a design aid, not a substitute for a qualified marine electrician.
Can it handle air-con and big loads?
Yes — add air-con, refrigeration and any custom load with its watts and hours, and it sizes the bank, inverter and wiring around them, moving to 24V or 48V where it makes sense.
Do I need an account?
No — design free with no email wall. Accounts are only for saving builds or the printable build binder.
The standards we build to
Plain version: these are the recognized rulebooks your design is sized against, so the numbers hold up to a surveyor, an inspector or an insurer.
ABYC E-11The US standard for AC & DC wiring on boats — what a surveyor or insurer actually checks.
ISO 13297The international standard for small-craft electrical systems.
ABYC 11.10The fault-current (AIC) rule for sizing the main battery protection.
Wattonomy applies these standards in its calculations. It is not certified, sponsored or endorsed by ABYC, ISO, NFPA or Victron — it sizes your design to meet what they require, and shows the working.
Sized and checked to ABYC E-11. Last reviewed June 2026 — see the full methodology for the exact rules behind every number and how each design is validated.
Built by anABYC Certified Master Technician