3 min·Original educational content

Conventional formula

Hours = usable_fuel_l / consumption_l_per_h; distance_nm = hours × speed_kn

In plain language

Estimated hours are usable fuel divided by hourly consumption. Estimated distance multiplies those hours by the relevant speed. Reserves, unusable fuel and conditions require separate consideration.

How to interpret it

Speed through water and speed over ground differ. Current, wind, waves and hull or propeller fouling change the real outcome.

Why it matters

Logs from the individual boat, with engine speed, loading and conditions, are more useful than a power-only assumption.

Limitations

A 100-litre tank does not mean 100 litres are available for a trip. This calculation is educational, not a navigation plan.

In practice

Hypothetical example: 60 usable litres at 3 l/h gives 20 hours; at 5 knots, 100 theoretical nautical miles before adjusting for conditions.

Do not use operationally without reserves and assessment of conditions.

Sources & reading

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