“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.