Now that fuel is almost as expensive as vintage cognac, it's time to keep closer tabs on how much your boat is using: A fuel-management system is an affordable way to do this and relatively straightforward to install. The simplest systems consist of an analog gauge displaying consumption in gallons (or liters) per hour; sophisticated models have digital gauges that provide gph, total fuel usage, fuel remaining, and if interfaced with a GPS, miles per gallon. You should choose one that provides at least gph and total fuel usage; you can figure out the rest with a calculator.
What can a fuel-management system do for you? The gph reading provides immediate feedback on how thirsty your engine is at any rpm. Crunch that number with boat speed to see how adjusting throttle, load, and trim affect miles per gallon. You'll also see the effects of adverse sea conditions, headwinds, and currents. (Systems that interface with GPS calculate mpg for you.) An abnormal increase in consumption can alert you to problems; maybe your engines have dirty spark plugs, clogged injectors, a damaged prop, or even a fuel leak.
The total-fuel-usage number shows you how much you've burned since you reset the counter; simple math will tell you what's left in the tank at any time. (Some fuel-management systems do this for you.) This provides peace of mind—the management system is usually more accurate than the fuel gauge—and can help save fuel, too: You don't have to fill the tanks, and therefore carry more fuel (and thereby more weight) than you need. Keep track of how much you add at every fuel stop by entering it in your log or inputting it into your fuel-management system, and you'll always know how much you have left.
Fuel-management systems typically consist of a display unit at the helm wired to flow sensors in the fuel lines. A basic, one-gasoline-engine setup with one sensor and an analog display costs about $500, a digital model around $800. For twins, most people use two separate systems, but you can save a few bucks by opting for a two-in-one display like FloScan's TwinScan. Pictured here, it shows the fuel burn of both engines simultaneously on a single gauge. Or you can connect two sensors to a single display through a toggle switch.
Diesel systems cost substantially more because they require two fuel sensors per engine, one in the supply line and a second for the return. Almost all diesels cool their injectors with excess fuel, so the flow sensors on the return lines have to compensate for the heated fuel, too. And the display must be more sophisticated, since it has to crunch the numbers from both sensors to arrive at a net fuel burn. Figure on spending around $1,000 for a basic single-engine diesel system and substantially more for digital and/or multiple-engine setups. More sensors also mean a more complex installation, maybe one you'd rather turn over to the boatyard—especially if you're not comfortable cutting your fuel lines.
If your engine is electronically controlled, you may have fuel management data already, probably in the engine computer. All you may need is a digital display for it. You may even be able to show fuel data on your multifunction display. Using the NMEA 2000 protocol, many electronics packages can accommodate input from a fuel sensor. Read the manual, check the manufacturer's Web site, or consult your electronics guru.
However you do it, it will pay you to manage your fuel. Use the money you save to buy a nice bottle of cognac.
Ask the Experts: Michael Peters
The question: The price of fuel is keeping me from using my boat as much as I'd like to. Is there any way I can cut the burn and get on the water more often?
The answer: Naval architect Michael Peters works in an office in Sarasota, Florida, but he lives on the cutting edge. Peters' custom yachts, sportfishermen, and production boats lead the fleet in style and performance, while his raceboats have set umpteen records and won many international trophies, including a couple of World Championships. Since 1981 more than 20,000 boats have been built to his designs. Now that fuel costs are skyrocketing, he's developing yachts that will balance economy with performance. In reference to your question, he has bad news and good news.
The bad news? "There's not a whole lot you can do with the boat you've already got," Peters says. Get rid of excess weight by offloading unnecessary gear, keep the bottom clean, and use the right prop(s). "Even a small reduction in weight will show up [in reduced fuel burn], but the amount you can take off probably isn't enough to make a real difference."
The good news? Help is as close as your throttle lever. "The best way to save fuel on the average boat is to rethink why you have to go fast," Peters says. "Is speed the fun you're getting out of boating? If you back off on the throttle, you save fuel not on a linear, but on an exponential basis: It takes four times the power to go twice as fast. So the biggest thing when it comes to saving fuel is, slow down." Get onto plane and just cruise there, he advises.
Once you decide you can live with less speed, modify your boat to operate efficiently at the lower speed, Peters says. "Reprop so the boat gets over the hump easily and runs there efficiently," he says. The problem with powering for maximum top end but running slower most of the time, he explains, is that you're spinning a big engine at an inefficient speed.
When it's time to repower, you might be pleasantly surprised by the new engines, as Peters was. His Bertram 25 had a 425-hp Mercruiser 502, which he replaced with a 365-hp 454 Volvo Penta. "I expected losing 60 hp would make the boat slower—but the new engine is lighter, with more torque buildup at lower rpm," he says. "Using the same prop, the same lower unit, the boat performs just as well as before but burns way less fuel."
Peters is excited about the challenges ahead. He predicts yachts will get greener soon and expects tomorrow's yachts will be longer, narrower, and lighter. "That's the way to go if you want efficiency."
This article originally appeared in the August 2008 issue of Power & Motoryacht magazine.