What Is Cruising RPM?
The rev range where the engine works efficiently and comfortably - the point where fuel, noise and engine life all win at once.
Cruising RPM is the rev range where the engine can run healthily for long periods and where efficiency is at its best. As a rough rule, it is around 70-80% of nominal (maximum) revs. A far more useful question than 'how many knots at full throttle' is this: at what revs, how many litres, over how many miles?
Choosing the right revs affects three costs at once: fuel, engine life and comfort. The table below sets out the rev ranges and what to expect from each.
Rev ranges
Range | As a % of nominal | Result |
|---|---|---|
Continuous idle / very low | < 40% | Sooting and glazing in diesels, carbon build-up in the turbo |
Cruising band | 70-80% | Best efficiency, engine running comfortably |
Continuous near full throttle | > 90% | Heat and wear, wasted fuel |
A single afternoon’s test can teach you a lot: in calm water, note speed and fuel burn every 200 rpm. The pattern you get is your boat’s fingerprint; the point with the lowest litres per mile is your true cruising RPM, and it often turns out to be a few hundred revs away from what owners expect.
Note: if the engine cannot reach the maker’s nominal revs at full throttle, the cruising RPM discussion comes later; first find the cause (propeller, fouling, load).