Marine Fuel Consumption Calculator

A common rule of thumb from the marine industry is: fuel consumption (gph) = horsepower * BSFC / fuel weight per gallon. For gasoline engines at cruise, brake specific fuel consumption (BSFC) is approximately 0.50 lbs/hp/hr. Gasoline weighs 6.1 lbs/gallon, so: gph = HP * 0.50 / 6.1. For diesel, BSFC is approximately 0.40 lbs/hp/hr and diesel weighs 7.2 lbs/gallon.

BSFC stands for Brake Specific Fuel Consumption, the mass of fuel burned per unit of power per unit of time (lbs/hp/hr or g/kWh). It is the standard marine engineering measure of engine efficiency. A lower BSFC means a more efficient engine. Modern diesel marine engines typically achieve 0.35 to 0.45 lbs/hp/hr at cruise; gasoline engines range from 0.45 to 0.55 lbs/hp/hr.

Marine engines are most fuel-efficient at 70 to 80 percent of maximum RPM (cruise throttle). At full throttle, fuel consumption rises disproportionately relative to power output. Many planing hulls have an efficient mid-range speed where fuel economy is maximised; running at maximum speed can double or triple fuel burn per nautical mile.

Fuel economy varies enormously. Small outboard boats might achieve 5 to 8 nautical miles per gallon at cruise. Mid-size stern-drive cruisers typically achieve 1 to 3 nm/gal. Large twin-engine sportfishers may achieve 0.5 to 1.5 nm/gal. Displacement trawlers with efficient diesel engines can achieve 3 to 6 nm/gal.

Yes. Rough seas increase fuel consumption by 10 to 30 percent as the vessel pitches and rolls, requiring more power to maintain speed. Headwinds and adverse currents also increase consumption significantly. Fuel range calculations should always include a safety margin of at least 15 to 20 percent for adverse conditions.