Burning Fuel Matters

How to maximize your miles per gallon.

11th June 2011.
By Pete McDonald

For years, the gold standard in boat marketing has been top end speed. Manufacturers have done everything possible to squeeze out an extra mile per hour or two, just so they can label their product a 50-mph boat. But, in this day and age of high fuel prices, maybe the gold standard should shift from MPH to MPG, as in Miles per Gallon.

How you run and maintain your boat can have a significant effect on your fuel efficiency.

Some of the best running outboards burn upwards of 3 mpg running at peak efficiency. Running 50 mph is going to shrink that number well below a mile per gallon, so the most obvious solution is: Slow down. Here are a few other ways to improve your gas consumption.

The Sweet Spot
For most anglers, making runs of 20, 40 even 60 miles one way is all in a day’s work. Running all out or just off wide open throttle is not good for your engine, and the extra burn will add up to a staggering amount of gallons burned at day’s end. The key is to make extended runs with the throttles firmly locked on the boat’s sweet spot.

What is the sweet spot? Most engines settle into it shortly after the boat climbs onto a plane. Once planing speed is reached, trim the engine up slightly until you can feel it lock in, almost humming with machine happiness. It’s definitely a feel thing, but there are defined parameters in which to work.

For most boats, an engine’s most efficient running speed falls between 25-30 mph. Diesel engines find their sweet spot somewhere beyond 1800 rpm. Gasoline outboards usually find it between 3000-4000 rpm. Every individual boat will have a different sweet spot depending on weight, power-to-weight ratio, prop selection, length-to-beam ratio, hull shape, deadrise, trim angle and other factors.

Digital Awareness
Today’s engines all have electronic control modules designed to shoot the leanest fuel amount possible into the cylinder and still perform. Most new boats have digital engine gauges to help chart your fuel efficiency. Mercury’s SmartCraft system is a prime example; it includes software called the Eco Feature that automatically calculates your boat’s sweet spot for you. Yamaha makes digital fuel monitors, too. If they’re not standard, they’re a worthwhile upgrade.

Your other electronics onboard can also help, especially your nav software. The old maxim you learned in geometry holds true on the water: the shortest distance between two points is a straight line. When running long distances, varying just a few degrees here and there will add miles to your cruise. Straying 10 miles, collectively, over the course of a trip could translate into burning 20 or more gallons of fuel. If gas hovers around $4 per gallon, that’s $80 burned away. Use your plotter to chart the shortest, most direct course possible and you could save hundreds, maybe even thousands, of dollars over a season.

Horses and Props
The common wisdom floating around the docks is that buying a smaller engine will save fuel. That is true only up to a point. One of the least efficient things you can do is underpower your boat. A smaller engine will have to work much harder to get the same results, and pushing it to higher rpms will eat into the mpg gains that might be there on paper.

Whatever powerplant you choose, the prop is an important component for running a boat at peak efficiency. Boats should be propped so they operate in the recommended top rpm band with a full load of fuel, gear, and people. The wrong prop could cause your engine to dog it a bit, under-revving or over-revving depending on whether it’s under or over-propped. If you’re not getting your desired numbers, the wheel spinning in the water is an obvious place to look.

Don’t Be A Drag
Outside of engine operation, one of the best ways to improve efficiency is to run with a clean bottom. Barnacles and algae growth can exacerbate drag, robbing you of speed and miles per gallon. The best thing to do is run a bare fiberglass hull. Waxing may make the bottom feel smooth but it holds air bubbles close to the hull, creating more friction. Adding bottom paint will slow your boat, but if you keep it in a slip, it beats the hell out of growth.

Another way to run more efficiently is to trim the fat. What do you absolutely need on board and what can you leave at home? Packing light helps. So does keeping the bilge and the insole lockers clean, and draining the baitwells when not in use.

Treat your boat like a contestant on the Biggest Loser, and you’ll come out winning.

Pete McDonald writes for Boating, Yachting, and other marine and fishing publications. In the past, he has written for Power & Motoryacht and Salt Water Sportsman, and spent 11 years on staff as a technical editor at Boating. All things considered, at any given moment he would prefer to be fishing.


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About the author:

Pete McDonald

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Pete McDonald is a contributing editor to Power & Motoryacht. Previously, he spent 11 years on the editorial staff of Boating. He has won multiple writing awards and holds a master’s degree from the Columbia University Graduate School of Journalism.

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