Short answer
Record hours, date, what was done, the exact part numbers used, the fluids and grades, any test readings, and what you found — not just what you replaced. Findings are what make the next fault diagnosable, and a documented history is one of the few things that measurably supports a boat's value at sale.
You will need: Logbook or spreadsheet, camera, receipts
Most owners record that a service happened. The useful record captures what the service revealed.
What to capture every time
- Hours and date. Both, always — the two clocks that drive every interval.
- What was done, item by item.
- Exact part numbers for filters, impellers, belts, anodes and fluids. This turns next year's parts order into a two-minute job.
- Grades and quantities of oil and coolant.
- Test readings: oil pressure, temperatures, charging voltage, maximum attainable rpm.
- Findings: the state of the old impeller, what was in the filter bowl, anode wear, weeping joints, anything noted and left. This is the column that pays.
Photographs cost nothing and record more than a line of text.
For drives and generators
Saildrives need dated evidence of diaphragm replacement, pressure tests, the coating system and anode type. Shaft drives need seal, bearing, alignment and propeller records. Generators should record electrical load during testing, not merely running hours — a genset that has only ever run lightly loaded is a different proposition from one properly worked.
Why it is worth the ten minutes
When troubleshooting, records reveal exactly which change preceded the problem. When selling, organised records reduce a buyer's uncertainty, and uncertainty is what buyers discount for. See records and the used engine survey.