"How much fuel will it burn?" is one of the most-asked questions at a marine dealer's showroom. It certainly is a question we get tons of mail about. But you might not realize that the answer to that question is largely in your own hands: It's in the way you handle the throttle. It's also in the way you load or overload your boat and the way you trim it. There are more than a half-dozen contributing factors to an overindulgence at the fuel pump, so to give you the best tools to boat green and save gas, we tapped our contacts at the Ralph Evinrude Test Center in Stuart, Florida.
Working hand in hand with the engineering staff, we formulated test procedures to measure the cost of poor boating habits and confirmed the validity of the results. These Evinrude guys eat, sleep and drink boats and motors, and so they proved a valuable resource in developing data you can count on.
So what did we learn? Depending on how many gas-guzzling habits you have, you could be costing yourself a double-size fuel bill each outing. We're about to show how to shave that bill down to size.
Props, Tops and Trim
We get tons of mail about which propellers are best for a particular boat. Unlocking the secrets of fuel efficiency on our Bluewater 2550 can give you insight for correctly propping your own boat. "Props are important to efficiency," deadpanned Mike Rogge, senior engineering technician for Evinrude and our prop specialist for this test. His no-nonsense delivery and demeanor confirmed our instinct to test the effects of props on fuel burn with him.
It's important to note that the primary criterion for selecting a propeller is to make sure it allows the engine to "turn up" to a speed within the band designated by the manufacturer - usually within 500 revolutions of absolute top rpm. This ensures a long life for the engine, neither lugging it down nor letting it over-rev. But within that band, you can select a variety of props that will allow the engine to turn up, yet have differences in pitch and number of blades, plus possess more subtle characteristics such as rake, skew and cup. Evinrude offers demo props through participating dealers for the purpose of allowing their customers to pick the best props for their needs.
Our Bluewater was run and turned up with eight different stainless-steel propellers. Not only did fuel consumption vary wildly, but also the thirstiest set of wheels allowed the engines to rev up only to the low end of the range specified by the manufacturer. The most fuel-saving wheels allowed the motors to rev to near the maximum of that range, however, meaning they'll not only save dinero at the pump, but will also pay dividends in increased long-term durability and reliability.
So, the right prop matters, meaning it's worthwhile to beg, borrow or steal a selection to try out on your boat. What else can help improve your boat's efficiency?
"You'll never have optimum fuel economy if you don't use optimum trim," says Steve Kocourek, Evinrude senior engineering technician. Testing bore out the veracity of Kocourek's statement. During extensive discussion he hammered home the fact that trimming out reduces the wetted surface of the hull by raising the bow. How do you know if you're trimmed for efficiency? "Trim out until the prop ventilates a little (sucks air). Then bring it down a little," Kocourek says.
T-Tops, Hardtops, Towers
Not every technique we tested saves as much fuel as does spinning the right prop or optimizing trim. Canvas enclosed T-tops, hardtops, towers and Bimini tops all create aerodynamic drag, causing the engine to work harder to make the boat go any given speed. Over the course of my career I've tested boats with the canvas up and the canvas down, and I've seen enclosures scrub as much as 3 mph off of a boat's speed. interestingly, some T-tops actually enhance efficiency: They act as a wing and create lift. But once you put canvas on, life's a drag once again.
Even something as simple as opening or closing a split windshield can affect how much go-juice the engine drinks. Our Bluewater's top wasn't removable, nor was it fitted with canvas, so we jumped into the first Chaparral 327 SSX bowrider to come off the line (read a full review) and tested it with the split windshield open and closed. Then we compared the results. This time, the economy was better with the windshield open, but for most bowriders, closing the windshield results in greater speed at a given rpm and, thus, better efficiency. Try your boat both ways, monitoring tach and speedo, to see what's best.
OK, so you won't be repowering with the money saved by closing or opening a windshield. Fuel economy is improved by a combination of tactics that incrementally add up to less fuel burned.
Article courtesy of Boating Magazine. To subscribe or view additional news from Boating Magazine, go to (www.boatingmag.com).