The 60-second diagnostic
The WOT test: one minute that reveals your propeller.
Warm engine, calm water, clean hull — full throttle for sixty seconds, and note the maximum RPM. Compared against the engine plate, that single number tells you whether your propeller is right, over-pitched, or under-pitched.
How to run it properly
- Warm the engine to operating temperature first.
- Calm water, light wind — you want the hull's honest resistance.
- Clean hull and prop — fouling fakes over-pitching perfectly.
- Full throttle, held 60 seconds, in ahead, trim normal.
- Note the maximum steady RPM the tacho settles at.
Why most production boats fail it
Builders prop for the brochure day: light boat, clean hull, flat water. Add cruising payload, a season's growth and real weather, and the same propeller is over-pitched — which is why so many owners have simply never seen rated RPM. It isn't the engine's fault, and it's completely fixable.
Correct pitching feels different immediately: the engine spins up willingly, reaches its numbers, and cruises at lower revs for the same speed — the pattern in every measured test.
Enter both figures for the verdict. Test conditions: warm engine, calm water, clean hull, full throttle held for 60 seconds.
Next step
Failed the test?
Questions owners ask
I'm 300 rpm short — how bad is that?
Meaningful. A diesel held below rated RPM at full fuel runs high cylinder pressures with reduced cooling — black smoke now, glazed bores over time. It also means your cruise is mis-geared, which is where the fuel goes. Re-pitching or correct sizing recovers it.
Can I just get my current prop re-pitched?
Often, yes — a workshop can re-pitch a bronze wheel a modest amount. Whether that's the right fix depends on how far out it is and what the boat needs; the Builder's sizing tells you whether adjustment or replacement makes sense.
I pass the WOT test but the boat still feels slow.
Then pitch isn't your problem — look at drag (under sail), fouling, and what sisterships run. The symptom checker walks the same logic an engineer would.
Get the numbers checked for your exact boat
The Builder takes your WOT result, engine and gearbox figures, and comes back with sizing verified by an engineer.