Before computers provided fuel-consumption data in our vehicles, we used a basic formula for determining gas mileage:
- Note miles on odometer at fill-up.
- Drive several hundred miles.
- At next fill-up, record gallons pumped, note miles on odometer.
- Subtract first odometer reading from second.
- Divide miles driven by gallons pumped.
But that process only gave us an average fuel burn over time. Today's monitoring systems - on cars and now vessels - let us know in real time whether we're operating efficiently.
"Fuel economy is obviously a big push button for a lot of people. It's something engineers are always working on - a constant point of focus and emphasis," says David Meeler, product marketing information manager for Yamaha.
Outboard manufacturers now make it fairly foolproof for boaters with newer engines to operate their vessels at peak efficiency simply by adjusting throttles and trim tabs while watching a digital display. But boats with any kind of power can benefit from easy-to-install, aftermarket fuelflow meters.
Most, if not all, marine outboard companies - Yamaha, Mercury, Evinrude, Suzuki, Honda, Nissan, Tohatsu - make computer-controlled engines. A command module in the powerhead gathers information from sensors placed throughout the engine. The module transmits that data to a vessel's gauges and/or to a multifunction electronics display (using NMEA 2000), which shows a wide variety of stats.
The kind of stats and their customization - including fuel-management details - depends on the type of gauges or MFD you use. Gauges and displays also must be compatible with the engine model. In Yamaha's case, Command Link (2006) and Command Link Plus (2009) gauges provide fuel-flow data (www.yamahaoutboards.com). They may be installed with a new engine or added as an upgrade for several hundred to several thousand dollars, depending on the equipment required. Yamaha also offers a less-expensive paddle-wheel system.
Instead of using a mechanical device that sends an electrical current to a gauge, Yamaha's newest systems are purely electronic. "It comes directly from the ECM (engine control module) and the fuel-mapping that's in there and the sensors on the engine," Meeler says. "It knows how much fuel it's injecting."
Meeler says the stat that most obviously and reliably translates to fuel efficiency is miles per gallon, which most of us quickly identify with from our vehicles. To calculate that number, Yamaha gauges must be connected to a mechanism that collects speed information such as a GPS (via NMEA 0183) or a triducer.
If you use a NMEA 2000-capable electronics display from companies such as Lowrance, Garmin, Raymarine, Furuno, Simrad, Geonav and others, you can buy a patch cable that marries Yamaha's ECM output directly to the display. Other outboard companies use similar bridges to nav displays or connect directly to a NMEA 2000 MFD.
If your display or gauges read only gallons per hour, you can convert that to mpg with this formula: mph ÷ gph = mpg. "You want to know how far you're going with a gallon of gas," Meeler says. "Look at that number more than others."
Yamaha publishes performance bulletins on its website for a variety of hulls paired with the company's engines, but every boat has its own "sweet spot." And that sweet spot might change on any given outing, based on load and conditions.
To find that spot, accelerate until your vessel is planing, then watch mpg. Increase rpm in increments of 500 until mpg stabilizes at its greatest level. Then adjust trim tabs to fine-tune the reading.