“How much does it burn?” sounds like a simple question. On a motor yacht it is not. A single number taken from a brochure cannot describe fuel consumption at displacement speed, economical cruise and full throttle — and it says nothing about generators, reserve, weather or the condition of the yacht being purchased.
The difference is financially significant. On a larger yacht, a small percentage error can mean thousands of litres, a different bunkering stop or an unsafe margin on a passage without a convenient alternative.
The real-range formula
A useful starting point is:
real range in nautical miles = (usable fuel in litres ÷ total consumption in litres per hour) × speed over ground in knots.
“Usable fuel” is not the tank’s advertised capacity. It is the amount left after an appropriate reserve has been removed. “Total consumption” must include generator demand when generators draw from the same tanks, or that demand must be subtracted from available fuel before the calculation. Speed over ground, not speed through the water, determines progress along the route.
The answer remains a forecast until confirmed on the exact yacht in conditions comparable with the intended passage. A shipyard trial may have been completed with a clean hull, light stores, calm water, low hotel load and favourable current. A used yacht carrying a tender, toys, provisions and years of added equipment is a different vessel in practical terms.
Five places where range disappears
The first is weight. Optional equipment, water, fuel, stores, guests and personal belongings change displacement and trim. The second is hotel load. Air-conditioning, watermakers, cooking, electronics, battery charging and stabilisation can require generator hours even when the main engines are operating efficiently.
The third is hull and running-gear condition. Growth on the hull, damaged coating, imperfect propellers or incorrect trim increase resistance. A factory-new test boat and a yacht that has spent weeks in warm marina water will not produce identical numbers.
The fourth is weather and current. Engines can be operating at the same load while speed over ground falls. The hourly consumption looks stable, but the yacht covers fewer miles and the range on the chart contracts.
The fifth is reserve. The last litres in the tank should never be treated as passage fuel. The U.S. Coast Guard’s recreational guidance refers to the familiar thirds principle: one part out, one part back and one part in reserve. Larger yachts require a reserve tailored to route, forecast, alternative ports and confidence in the available performance data. The important point is that a reserve is selected before departure, not discovered when the gauge falls faster than expected.
What a buyer should request
One “best” range figure is not enough. Ask for the complete table connecting engine rpm, speed and combined litres per hour. Then request the test displacement, fuel and water levels, number of people aboard, sea state, wind, temperature, current, generator status and the method used to calculate reserve.
For a used yacht, separate three sets of evidence: the model’s published data, the individual yacht’s original trial report and a current sea-trial or survey result. The brochure describes a design. It does not automatically describe the yacht after refits, equipment additions, charter use or deferred maintenance.
This is where a buyer-focused review differs from marketing. Good shipyards publish methodology and limitations. The warning sign is not an optimistic number by itself; it is an optimistic number without the inputs needed to reproduce it.
Fuel data is also technical due diligence
Unexpected consumption can reveal more than an expensive passage. It may point to hull fouling, damaged propellers, overloaded configuration, incorrect engine loading, injector problems or poor trim. A controlled sea trial should therefore record rpm, speed through water, speed over ground, fuel flow, engine load and relevant temperatures at multiple operating points.
The same logic applies when evaluating a high-volume yacht such as the Sunseeker Ocean 82. Its range cannot be separated from hotel systems, generator demand and the way the owner intends to use its unusually large internal volume.
Before purchase, W Yachts can build a route-specific fuel model from the candidate yacht’s actual data: usable fuel, generator consumption, sea-trial results, hull condition, reserve and weather margin. The safest range figure is not the longest one in the brochure. It is the shortest credible figure the evidence supports.
