Water, ground or GPS speed for fuel economy?

[scharebear]

Which one of these speed sources should I use to calculate fuel economy when I set up my smis 4 inch gauges?
Water speed, Pitot speed, or ground speed?

[Harper]

Ground speed will work for sure if you have GPS outputting groundspeed info to the NMEA 2000 network. The other two will work if their output is to NMEA 2000 network, otherwise, ground speed is all you can use. A water wheel hooked into the network will give you water speed, I'm not sure how you'd get pitot speed to read out, but it's also just a water speed. Maybe some engines have the capability to send pitot speed, mine doesn't. I think you're best average fuel economy readings are going to be from ground speed (GPS) anyway, since it won't be altered by current and wind, or perhaps more correctly stated, it gives a true speed across the surface by not being affected by such elements.

[Moonlighter]

Agree with Mike. Everyone I know uses ground speed (GPS).

The DF300's and possibly some newer 250's output pitot speed to the network. But pitot speed is notoriously inaccurate anyway, plus it only takes some grit or seaweed to block it and you've got no data.

[scharebear]

Thanks for the help