Salt, heel and survey rules don’t forgive shortcuts. Wattonomy sizes your house bank, solar and alternator to real loads, then specs the tinned, fused, code-referenced wiring to match — so your boat’s power is something you stop worrying about.
A real Wattonomy output — a cruising sailboat house bank
System
12 V
Battery
7.68 kWh
Solar
800 W
Inverter
MP 12/1600
SmartSolar 150/701×
200W solar panel4×
Battery → inverter cable4×
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
Offshore, power failure isn’t an option.
A dead house bank at anchor, a fried alternator, or an under-fused battery in a fault — these are the failures cruisers plan against. Wattonomy sizes to ABYC E-11 and ISO 13297, puts an AIC-rated Class-T fuse on the battery, and shows the math a surveyor or insurer will respect.
What a sailing yacht needs to get right
Boats add constraints a van never sees — and the standards are stricter for good reason.
House bank
Sized to days at anchor and an honest depth-of-discharge, kept separate from the engine-start battery.
Charging sources
Solar + MPPT, plus alternator and shore power — balanced so you actually recharge between sails.
Class-T fusing & AIC
Lithium banks can deliver enormous fault current; we size the main OCP and AIC to ABYC 11.10, not guesswork.
Tinned, sized wiring
Every run gauged for ampacity and voltage drop in marine conditions, to ABYC E-11 / ISO 13297.
What you walk away with — free
A house-bank + solar design sized to your real loads
A wiring diagram with Class-T fusing and tinned-cable gauges
AIC-aware fuse sizing and voltage-drop, to ABYC / ISO
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
Is the design ABYC-compliant?
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’s sign-off.
Does it handle alternator and shore-power charging?
Yes — solar/MPPT plus alternator and shore power are balanced into the design so the bank actually recharges.
Drop-in or externally-managed lithium?
The tool sizes the bank and its protection to your loads; it shows the fusing and AIC so you can pair it with the right BMS/charging strategy for your boat.
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