Passage / Fuel Planning Calculator
Calculate boat passage time, fuel consumption, required reserve fuel, total fuel for a trip, and whether your available tank capacity is sufficient for the planned route.
Passage & Fuel Planning Results
What is a passage fuel planning calculator?
A passage fuel planning calculator estimates how much fuel a boat needs to complete a planned route. It combines distance, expected cruising speed, fuel burn, additional time, and a reserve allowance.
A basic calculation can be expressed as:
$$Travel\ Time = \frac{Distance}{Speed}$$
$$Passage\ Fuel = Travel\ Time \times Fuel\ Burn$$
How do you calculate boat travel time?
When distance and speed use compatible units, travel time is distance divided by average speed.
$$Time = \frac{Distance}{Speed}$$
For a marine passage, nautical miles and knots are convenient because one knot is one nautical mile per hour.
$$Hours = \frac{Nautical\ Miles}{Knots}$$
How do you calculate boat fuel consumption?
If fuel burn is specified in gallons per hour, multiply the expected operating time by the hourly fuel burn.
$$Fuel = Hours \times Gallons\ per\ Hour$$
For example, a boat consuming 20 gallons per hour for 3 hours would require approximately 60 gallons for that operating period before adding a reserve.
How do you calculate fuel reserve for a boat?
A simple percentage reserve can be added to the calculated passage fuel.
$$Reserve\ Fuel = Passage\ Fuel \times \frac{Reserve\%}{100}$$
$$Total\ Planned\ Fuel = Passage\ Fuel + Reserve\ Fuel$$
Why is fuel reserve important?
A passage rarely occurs under perfectly predictable conditions. Wind, waves, currents, speed restrictions, harbor maneuvering, waiting, detours, and changes in operating speed can all increase fuel consumption.
Reserve fuel provides an allowance for uncertainty, but the correct reserve should be chosen for the particular vessel, route, weather, distance offshore, and operating requirements.
How does speed affect boat fuel consumption?
Fuel consumption often changes significantly with speed, especially on planing powerboats. Therefore, fuel burn measured at one cruising speed should not automatically be applied to another speed.
Use a fuel-burn figure that corresponds as closely as possible to your intended cruising speed, load, engine condition, and sea state.
What is boat fuel economy?
Fuel economy describes how far the boat can travel for a given amount of fuel. When using nautical miles and gallons:
$$Fuel\ Economy = \frac{Nautical\ Miles} {Gallons}$$
The reciprocal relationship is fuel burn per nautical mile:
$$Fuel\ per\ NM = \frac{Gallons} {Nautical\ Miles}$$
What affects real-world boat fuel consumption?
- Engine speed and load
- Boat weight and loading
- Hull type
- Wind and wave conditions
- Current
- Propeller condition and selection
- Engine condition
- Trim and operating technique
- Water depth and sea conditions
- Idling and maneuvering time
Should I calculate fuel using maximum speed?
Usually, fuel planning should use the expected average speed for the actual passage rather than maximum speed. Maximum speed can produce a substantially different fuel burn and is rarely maintained for an entire route.
Should fuel planning include maneuvering time?
It can be useful to include additional time for departure, harbor entry, docking, waiting, restricted-speed areas, and other periods when the boat is operating but not covering the planned route at its normal cruising speed.
This calculator provides an optional additional time allowance for this purpose.
Does a round trip need twice the fuel?
A simple round-trip estimate doubles the planned one-way distance. However, actual consumption can differ between the outbound and return legs because wind, current, loading, and operating conditions can change.
How much fuel should I carry for a passage?
A planning calculation should cover the expected passage fuel plus an appropriate reserve. The result should also be checked against the boat's usable tank capacity and the actual route.
Why use usable tank capacity instead of nominal tank size?
The nominal tank capacity is not always the same as the amount of fuel that can actually be used during a passage. Tank geometry, fuel pickup position, trim, installation, and operating limitations can affect usable fuel.
Use the vessel manufacturer's recommended usable capacity or a verified onboard value when possible.
Passage fuel planning example
Suppose a boat travels 120 nautical miles at an average speed of 20 knots and burns 22 gallons per hour. The estimated travel time is:
$$Time = \frac{120}{20} = 6\ hours$$
$$Passage\ Fuel = 6 \times 22 = 132\ gallons$$
With a 20% reserve:
$$Reserve = 132 \times 0.20 = 26.4\ gallons$$
$$Total = 132 + 26.4 = 158.4\ gallons$$
The boat would therefore need approximately 158.4 gallons of usable fuel for this planning scenario.
Can fuel planning predict exactly when a boat will run out of fuel?
No. Fuel planning is an estimate. Real-world conditions can change consumption substantially, so the result should not be treated as an exact prediction of the remaining fuel at the destination.
Passage / fuel planning FAQ
Calculate travel time from distance and average speed, then multiply that time by the boat's expected fuel burn rate. Add an appropriate reserve afterward.
It depends on the engine, hull, speed, load, propeller, and operating conditions. Use a measured fuel-burn value that matches your intended cruising condition.
Divide the fuel consumed by the distance traveled: fuel per nautical mile = fuel used รท nautical miles traveled.
There is no single percentage suitable for every passage. Reserve should account for route length, weather, current, offshore distance, alternates, vessel characteristics, and operating requirements.
Yes. A head current can reduce effective speed over ground and increase travel time and fuel consumption, while a favorable current can have the opposite effect.
Yes. The most useful fuel-burn figure is one measured or provided for the same speed, loading condition, engine configuration, and operating conditions as the planned passage.