Boat Speed vs. Fuel Economy

Given the current level of fuel prices and their volatility, it’s a good idea to be aware of fuel economy when shopping for a new or used boat. Then again, fuel economy is probably high on everyone’s mind these days. What’s interesting is that a fuel-injected V6 from MerCruiser or Volvo-Penta can often be as powerful as an older carbureted V8. Even better, a V6 with EFI in nearly all cases will be more fuel-efficient than a V8 with a carburetor.

Every boat has a “sweet spot,” the point at which trim setting and engine speed yields the greatest fuel efficiency. By knowing your fuel-flow numbers, you can get the most out of a tank of a gas. Mercury's SmartCraft system, shown above, can monitor fuel flow.

I say in “nearly all cases” because there might be some remote instance in which they aren’t, and some smarmy third-year engineering student would smarmily write some smarmy comment in the comments section of this blog. But you get the idea.

The point is that a used boat with a fuel-injected V6 might be more expensive up front than one that is, say, a few years older and has a carbureted V8, but over the length of ownership, would actually be cheaper to operate based on fuel costs alone. That’s why it’s important to know fuel flow at different speeds. Some magazines and websites publish those numbers, and a manufacturer might make them available, but if a boat has a system like Mercury’s SmartCraft, you can toggle to fuel-flow mode on your test drive and monitor it yourself.

Let’s say you were headed to your favorite waterfront restaurant 40 miles upriver. What speed would yield the best fuel economy, yet allow you to arrive at your destination within a reasonable amount of time? In the example below, the Formula 240 Bowrider works best at 3,500 rpm. That engine speed, combined with an appropriate trim setting, lets you cover the most ground in the shortest time with the best fuel economy. Yes, it’s a V8, but the consumption curve is the same for a V6.

Boat: 2008 Formula 240 Bowrider

Engine: MerCruiser MX 6.2 MPI, 320 horsepower

Drive: MerCruiser Bravo Three

RPM   MPH   GPH   Time to 40 miles       Fuel Burned  MPG   Total Fuel Cost*

1,500   7          3          5 hrs. 42 min.             17.1 gal.          2.3       $76.95

2,000   9          5          4 hrs. 24 min.             22.0 gal.          1.8       $99.00

2,500   16        7          2 hrs. 30 min.             17.5 gal.          2.3       $78.75

3,000   25        9          1 hr. 36 min.              14.4 gal.          2.8       $64.80

3,500   32        11        1 hr. 15 min.              13.8 gal.          2.9       $62.10

4,000   37        15        1 hr. 6 min.                16.2 gal.          2.5       $72.90

4,500   43        18        56 min.                       16.7 gal.          2.4       $75.15

5,000   49        23        49 min.                       18.6 gal.          2.1       $83.70

* Based on $4.50 per gallon

By knowing your fuel-flow numbers, you can get the most out of a tank of a gas. So when you get to your favorite restaurant, you can use the money you saved filling up the boat to fill up on appetizers.

For more on this, follow the links at Fuel-Saving Tips for Boaters.

- Brett Becker

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