“How much gas does it use?” is a fair question when you’re looking at a boat. The answer gets confusing when one seller gives you gallons per hour, another says miles per gallon, and a third just says it’s great on fuel.
There isn’t one useful average MPG for every boat. Compare the specific boat and engine package, the speed, the load, and the units behind the number. A fuel figure without that context can make two very different boats look more alike than they are.
Here’s a simple way to understand the numbers for shopping and fuel-cost comparisons. This is not a passage-planning guide or a promise of how far a tank will take you.
MPG and gallons per hour answer different questions
- Gallons per hour (GPH): how much fuel is consumed in an hour at the stated operating condition.
- Miles per gallon (MPG): how many statute miles are traveled for each gallon consumed.
- Nautical miles per gallon: the same kind of distance-per-fuel measure, but using nautical miles.
- Gallons per mile: fuel used for each mile. This is the inverse of miles per gallon, not another name for it.
Keep the gallon unit consistent too. Don’t mix U.S. gallons and Imperial gallons in the same comparison.
The basic MPG calculation
For speed and fuel flow measured over the same operating period:
Speed in miles per hour ÷ fuel use in gallons per hour = miles per gallon.
For a made-up example, 24 mph divided by 8 U.S. gallons per hour is 3 miles per U.S. gallon. Those are teaching numbers, not a test of a particular boat.
If the speed is in knots, the result is nautical miles per gallon. NOAA explains that one knot is one nautical mile per hour, and one nautical mile is about 1.1508 statute miles.
So 20 knots divided by 10 U.S. gallons per hour gives 2 nautical miles per U.S. gallon, or about 2.30 statute miles per U.S. gallon. Calling both answers “2 MPG” would hide a real difference in the units.
What a real performance bulletin can tell you
A manufacturer’s bulletin is more useful than a universal “average boat MPG” because it identifies a particular setup.
For example, Yamaha’s July 28, 2023 test of a Veranda Vista 22RC with a single F175LA lists 21.8 mph, 4.5 GPH and 4.79 MPG at 3,500 rpm. At 5,500 rpm, it lists 38.5 mph, 15.3 GPH and 2.51 MPG. These are the bulletin’s published values, not our own test results.
The same bulletin records the tested load and conditions and warns that actual performance can differ. That is why the exact boat, engine package, load and test conditions belong beside the fuel number. See the Yamaha bulletin and its qualifications.
Use a report like that to ask better questions. Don’t turn one test point into a guaranteed figure for your boat, or assume it tells you the right operating speed for a particular day.
Compare fuel cost, not just the biggest MPG number
For a simple operating-cost comparison, multiply fuel consumption per hour by the price per gallon.
Using hypothetical numbers again: 8 U.S. gallons per hour at $5 per U.S. gallon equals $40 per operating hour at that fuel rate. The $5 price is an example, not a current marina quote.
An outing can include different speeds and time with the engine off, so one hourly figure should not be presented as the exact cost of every day on the water. Keep fuel separate from storage, insurance, maintenance and the other costs of ownership. Our boat-buying decision guide helps put that bigger picture together.
Questions worth asking before you buy
- Which exact model year, hull, engine package and propeller does the fuel figure describe?
- Is the speed in mph or knots, and are the gallons U.S. or Imperial?
- Is fuel burn shown for the whole boat or for one engine?
- What speed, rpm, passenger load and conditions went with the number?
- Is this a manufacturer’s test, a seller’s measured record, or an estimate?
A useful message to a seller is: “Do you have fuel-use records or a performance bulletin for this exact setup? I’d like to see the speed, total fuel burn and load behind the number.”
If you’re comparing several boats, keep those answers together in the free used-boat buyer kit. An unknown answer is worth writing down too.
So, how far can you go?
A generic MPG article cannot answer that safely for your boat and trip. Don’t use the example calculations here as a fuel allowance or a maximum-distance recommendation. Actual fuel planning requires boat-specific information and allowance for the conditions and contingencies of the trip.
For shopping, the useful takeaway is simpler: get the units right, compare like with like, and ask where the numbers came from. That will tell you much more than a confident claim that a boat is “good on gas.”