Sailing boat – fuel triangle
Navigation tool

Fuel triangle  ·  Fuel, flow and time

Fill in two of the three fields in the triangle – the third is calculated automatically. Plan fuel quantity, passage time and consumption with this simple navigation aid.

B = Fuel (litres) Fl = Flow (l/h) T = Time (hours)
Try examples
Inboard diesel engine
How much do we use in 7 hours under engine?
B = ? Fl = 3 l/h T = 7 hours
Tank size known
Max. permitted flow over 8 hours?
B = 40 litres Fl = ? T = 8 hours
Reserve on board
How far will the fuel last?
B = 25 litres Fl = 4 l/h T = ?
Long-distance sailing
Fuel for 12 hours of auxiliary engine?
B = ? Fl = 2,5 l/h T = 12 hours
Interactive triangle
Fuel
B
litres
Flow
Fl
litres/hour
Time
T
hours
⛽
Understanding the triangle
B
Fuel
B = Fl × T
Multiply the flow (l/h) by the passage time (hours). Gives the total fuel consumption in litres.
Fl
Flow (consumption per hour)
Fl = B ÷ T
Divide the available fuel by the desired passage time. Gives the required flow in l/h.
T
Time
T = B ÷ Fl
Divide the fuel quantity by the flow. Gives the possible passage time in decimal hours.

⛽ Typical consumption guidelines

Diesel engine (inboard): approx. 2–4 l/h at cruising speed

Outboard engine (petrol): approx. 3–8 l/h depending on kW

The engine manufacturer's technical data gives the most accurate figure.

⚠ Safety rule: Always carry at least 1/3 extra fuel (33% reserve) as a safety margin for headwinds, current and miscalculations.
Brequired + 33 % = Bon board
Engine + sails combined: Note the engine's flow during trials in calm weather with GPS-logged speed. Make your own calibrated tables per rpm for precise planning.