Man with a Mission (How to Make a Boat Greener and Energy Efficient), by Ben Ellison (continued)
Mastering Fuel Burn
Installing a precision fuel-flow system doesn’t make a boat more energy efficient; it only shows the driver exactly how much fuel is being burned at a given rpm in given conditions. But that sure worked for me. While I’d long known that Gizmo is chronically inefficient in semi-displacement mode—at 17 knots she pulls a big wake and the Volvo Penta specs suggest she’s burning three times the fuel needed to go half that speed—adding Maretron fuel flow sensors made me much more aware of the nuances.
The sensors subtract the diesel being sent back to the tanks from what’s pumped in, and then send the result over NMEA 2000 to all the displays that can calculate miles per gallon, total gallons used, etc. The real-time nm/gal. number can be jumpy at low speeds, but the averages and totals are remarkably accurate, which I was able to confirm because Gizmo also has very accurate fuel tank level monitoring.
What I learned was that Gizmo is at least the fuel hog I thought at 17 knots but that pushing her up to 10 or 12 knots to be more comfortable in rough seas is more efficient than expected. Overall the positive and negative effects of wind and waves on my power boat are greater than I realized and being able to see the numbers is a real encouragement to cruise efficiently.
In fact, we were pleased to average 3.1 nm per gallon over a windy 740-mile fall run from Maine to Baltimore, though many of the sailors we passed would laugh at that figure. I joke that the real key to throttle behavior modification might be a money meter—just a computation of diesel per gallon cost with nm per gallon, which Maretron may enable on their gauges—but if some boaters use it to show off how much dough they’re spending, I won’t judge.