2026 Captain’s Edition
12V Load & Energy Budget Worksheet PDF
Measured Draw, Duty by Regime & Autonomy
- 23 Pages / 180 Register Lines A4 and US Letter included.
- 780 Live Fields Interactive and 100% offline.
- 6 Calculation Models B1 through B6.
- Instant Digital Access Download links the moment you pay.
The figure on the data plate and the figure on the shunt are not the same number — and the difference is never in your favour.
The plate figure was measured on a new unit, at a bench voltage, in a laboratory. Yours is ten years old, at the end of a long cable run, through a connection that is not what it was. Across twenty loads that gap is the difference between a bank that lasts three days and one that lasts one.
Every load in this worksheet has a column for what the appliance claims and a column for what it actually drew. It is the single column nobody fills in, and it is why most energy budgets are optimistic fiction.
What you receive
A seven-part worksheet built on measurement
- A 24-line reference page for the figures you transcribe from your own cells, monitor, inverter and data plates — including usable capacity, which is not rated capacity
- 28 loads measured at the shunt, plate figure beside measured figure, with the gap computed per load
- A 16-session measurement register recording ambient temperature and bank state, because two readings without them are not comparable
- The same 28 loads across four usage regimes — at sea, at anchor, in harbour, laid up — with a daily total and an autonomy figure for each
- 14 logged days comparing what actually happened against what the budget predicted
- 6 calculation models and a parasitic draw register for everything still live with the boat switched off
Four regimes, not one average
A fridge at anchor in thirty degrees and the same fridge under way on a cool passage are different appliances. A single averaged consumption figure is what makes people buy the wrong bank — too small for the Mediterranean in August, too large for a boat that mostly sits on a mooring.
This worksheet gives you four columns and four autonomy figures. The laid-up column is the one that surprises people: three weeks on a mooring with a bilge float, an alarm and an inverter on standby will flatten a bank that seemed generous all summer. Model B6 exists for exactly that.
Not one published consumption figure. Deliberately.
A table of typical draws copied from a forum is the single commonest reason an energy budget turns out wrong. Appliances differ by make, by age, by how they are installed and by how their owner uses them. You measure yours once, at your own shunt, and every calculation afterwards rests on your own boat.
Hours, not switch positions
The trap in an energy budget is never the current — it is the hours. A fridge is not on for twenty-four hours; it cycles, and the honest figure is total running time over a day. A windlass draws an enormous current for ninety seconds, which looks catastrophic expressed hourly and is a rounding error expressed per anchoring. The worksheet is built around getting that column right.
Fourteen days that test the arithmetic
Part IV logs real days against the predicted figures. A budget that survives contact with fourteen days is a budget; anything else is arithmetic. And where the two diverge, the fault is almost always in the hours rather than the current — which is worth knowing before you spend four figures on more battery.
How it completes the Electrical & Power set
The Lithium & DC System Record covers what stores the energy. The Solar & Hydro Yield Record covers what generates it. This one covers what spends it — and model B5 turns the whole thing into the one number that decides how you live aboard: engine hours per day.
Who it is for
- Owners sizing a new bank, or being quoted for one, who want measurements rather than assumptions
- Liveaboards and long-distance cruisers planning for passages rather than weekends
- Anyone whose batteries are flat after a few weeks away and who does not know what did it
- Owners adding a watermaker, a freezer or air conditioning who need the real cost first
Technical specification
| Product ID | AML-ELEC-2026-03 |
| Extent | 23 pages · 7 parts · 6 calculation models |
| Register lines | 180 across reference, measurement, regimes, observation and verification |
| Interactivity | 780 live PDF form fields — 38 tick boxes and 742 entry fields |
| Formats included | A4 and US Letter, both fillable and print-ready, 23 pages each |
| Systems | 12V or 24V, any chemistry, up to 28 loads — four lines unlabelled |
| Requires | A battery monitor with a shunt — the measurements depend on it |
| Offline | No app, no account, no connection required once downloaded |
What it is not
This worksheet records, structures and compares figures that you supply. It publishes no current draw, no duty cycle, no depth of discharge and no consumption figure, and it reaches no conclusion about any installation.
Sizing a battery bank, a charge source or a circuit is qualified work. An autonomy figure computed here is an estimate built on your own measurements — not an assurance that any bank will last any particular length of time at sea.
Instant download. Your links appear on screen the moment payment clears, and arrive by email within a minute. They do not expire.
2026 Captain's Edition · Revision 1.0 · AML-ELEC-2026-03. Apex Marine Labs designs the organisational process behind good seamanship. Our documents record and organise; they do not replace a certified marine survey, an installation standard, or a qualified marine electrician.