Outboard motors are the most common marine propulsion type for small watercraft because of their compact design. Generally, fuel efficiency can be summarized by taking the horsepower rating and dividing it by 10 and you get the gallons per hour number, but this article goes a little more in-depth.
To find much of the data on specific motors, I used boat-fuel-economy.com.
How fuel efficient are outboard motors on average?
By using the most popular outboard brands, I found the average of their fuel efficiency based on how much horsepower they had. Here are the results:
| Motor Horsepower | Average Fuel Efficiency |
|---|---|
| 10 hp | 1 GPH |
| 25 hp | 2.5 GPH |
| 40 hp | 3.9 GPH |
| 50 hp | 4.7 GPH |
| 60 hp | 5.5 GPH |
| 70 hp | 7.3 GPH |
| 90 hp | 9 GPH |
| 115 hp | 10.8 GPH |
| 135 hp | 13 GPH |
| 150 hp | 15 GPH |
| 175 hp | 16.5 GPH |
| 200 hp | 19.5 GPH |
| 225 hp | 21 GPH |
| 250 hp | 24.5 GPH |
| 300 hp | 26.2 GPH |
| 350 hp | 33.5 GPH |
| 400 hp | 38 GPH |
| 600 hp | 51 GPH |
The general rule of thumb is to take how much horsepower your motor has and divide it by 10. This will give you a good estimate on how many GPH you would be using.
Note- This is assuming you are driving near full speed the whole time, true numbers will vastly vary. The slower you go the less GPH it will be, but you will obviously not go as far in that hour.
What outboard brands are the most fuel efficient?
- Suzuki
- Yamaha
- Tohatsu
- Honda
- Mercury
- Evenrude
When it comes to fuel efficiency, all of these are very similar, but Japanise made outboards tend to be slightly more fuel-efficient.
How can you make your boat more fuel efficient?
The lower your boat wieghs, the more fuel efficient it will be. So getting a good bulg pump to get rid of water in the hull will help eliminate some weight.
Also, making sure your engines are running well and you are only using 91 rated fuel or no ethanol fuel will help keep your motors as efficient as possible.
Many people tend to idle a lot. Simply turning your engines off when you don’t need them will help use less fuel.
Lastly, just toning the throttle down slightly to 75% when traveling could save you loads of fuel.
How much do you spend each year on fuel for outboard motors?
Obviously, this number depends on how large your motor is, but we can do some calculations based on fuel efficiency. If you assume that you use your boat for 50 hours per year, here is how much gas you would use and how much it would cost:
| Horsepower | Gas Usage Per Year | Gas Cost Per Year |
|---|---|---|
| 10 hp | 50 gal | $125-$200 |
| 25 hp | 125 gal | $313-$500 |
| 40 hp | 195 gal | $488-$780 |
| 50 hp | 235 gal | $588-$940 |
| 60 hp | 275 gal | $688-$1,100 |
| 70 hp | 365 gal | $913-$1,460 |
| 90 hp | 450 gal | $1,125-$1,800 |
| 115 hp | 540 gal | $1,350-$2,160 |
| 135 hp | 650 gal | $1,625-$2,600 |
| 150 hp | 750 gal | $1,875-$3,000 |
| 175 hp | 825 gal | $2,062-$3,300 |
| 200 hp | 975 gal | $2,438-$3,900 |
| 225 hp | 1,050 gal | $2,625-$4,200 |
| 250 hp | 1,225 gal | $3,063-$4,900 |
| 300 hp | 1,310 gal | $3,275-$5,240 |
| 350 hp | 1,675 gal | $4,188-$6,700 |
| 400 hp | 1,900 gal | $4,750-$7600 |
| 600 hp | 2,550 gal | $6,375-$10,200 |
Are inboard motors more fuel efficient than outboard motors?
After comparing the two, inboard motors tend to be slightly more fuel-efficient than outboard motors. It is not by much though, it’s only about 0.5 to 2 GPH difference at most, so practically the same.
The data was collected comparing the Volvo Penta and Mercruiser with all of the outboard brands. An example of this difference is the Mercruiser 4.5 MP1 250 hp gets 19.7 GPH, while the Yamaha 250 hp motor gets 23.8 GPH. Both engines are V6.
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