Motor Yacht Fuel Efficiency Guide

Fuel is the single largest variable cost in motor yacht ownership, and motor yacht fuel efficiency varies dramatically with hull type, engine size, and cruising speed. A 15-metre displacement yacht may burn 8 litres per hour at 7 knots, while a similar-length planing yacht at 25 knots can consume 80 litres per hour or more. Understanding motor yacht fuel consumption before purchase allows a buyer to estimate annual running costs and choose a vessel whose fuel economy matches the intended cruising pattern. Buyers comparing motorboats on Owning should treat fuel burn data as a core specification, not an afterthought.

Hull type and the speed-efficiency curve

Hull form is the dominant factor in fuel economy. A displacement hull operates most efficiently at or below its hull speed — approximately 1.34 times the square root of the waterline length in feet — where resistance is minimal. A semi-displacement hull extends the efficient range to roughly 1.5 times hull speed before resistance climbs steeply. A planing hull is inefficient at displacement speeds but becomes economical once fully planing, though absolute consumption remains high because of the power required to maintain lift. The practical consequence is that a displacement motor yacht achieves the best nautical miles per litre, while a planing yacht trades fuel economy for speed. The hull types guide explains these hydrodynamic principles in greater depth.

Measuring and comparing consumption

Fuel consumption is best expressed in litres per nautical mile rather than litres per hour, as the latter obscures the effect of speed. A buyer should request the engine manufacturer's fuel consumption curve, which plots litres per hour against RPM and load, and then divide by the corresponding speed to obtain litres per nautical mile. Engine load matters: a diesel operating at 70 to 80 percent of rated power at cruise is generally near its brake-specific fuel-efficiency peak, while an overpowered yacht running at low load may suffer cylinder glazing and poorer economy over time. For a realistic annual estimate, multiply the planned cruising hours by the consumption at the intended cruising RPM, and add a 15 percent reserve for weather, tidal current, and generator use. Buyers planning extended passages should also review the maintenance cost guide, as engine service intervals scale with hours and fuel burn.