Boat EconomicsUse and Trip Economics
Does This Tank and Reserve Actually Support the Route?
An arithmetic planning check: fuel available after your chosen reserve, and whether a planned route fits it. Not navigation or safety guidance.
This is an arithmetic planning check only, not navigation, safety, or an authorization to proceed. It does not replace charts, weather, or route planning, and does not prescribe a reserve rule for you.
A full tank isn't the same as a full tank of usable, safe range
Tank capacity on a spec sheet is not what's actually available for a trip once a reserve is set aside for the return, weather, or an emergency. This engine only does the arithmetic: capacity minus reserve minus any idle allowance, divided by consumption, is the planning range. It does not decide what reserve is appropriate, that stays your call.
How this is calculated
Fuel available after reserve subtracts your chosen reserve (a flat amount or a percentage of capacity) and any idle/maneuvering allowance from usable tank capacity. Dividing that by your consumption rate gives a theoretical planning time; a cruising speed, if entered, converts that into a theoretical planning distance. If you enter a planned route's running time, the tool checks whether it fits within the fuel available after reserve and shows the margin either way.
Worked example
A 50-gallon usable tank with a 10-gallon reserve leaves 40 gallons available. At 5 gallons per hour, that's a theoretical 8-hour planning range. A planned 6-hour route fits with a 10-gallon margin; a planned 9-hour route does not fit, falling short by 5 gallons, a clear sign to shorten the route, add a fuel stop, or reconsider before departing, not to shrink the reserve to force the numbers to work.
Common mistakes
Using tank capacity instead of usable capacity overstates real range; not all boats can draw the last gallons in the tank. The other mistake is shrinking the reserve after the fact just to make a planned route fit the arithmetic, which defeats the reserve's entire purpose.
Frequently asked questions
Does this tell me it is safe to make a trip?
No. This is an arithmetic planning check only, using the numbers you enter. It does not substitute for charts, weather, route planning, or any safety judgment, and it never recommends proceeding with a trip.
What reserve amount should I use?
This tool does not prescribe a reserve rule; that is a judgment call based on your boat, waters, and experience, following manufacturer and authority guidance where it applies. Enter the reserve you have already decided on, in gallons or as a percentage of tank capacity.
Why does the theoretical range assume steady consumption?
Because that is the only way to compute a number from the inputs you provide. Real consumption changes with load, sea state, and throttle use, which is exactly what your reserve exists to absorb; this figure is a planning estimate, not a guarantee.
How is this different from Boat Trip Fuel Cost?
That engine estimates what a planned trip will cost in dollars. This one checks whether your tank, minus your reserve, actually has enough fuel for a planned route in the first place, a capacity and safety-adjacent question, not a cost one.