Auto guidance systems can cut mowing overlap losses in half, according to Matt Digman, University of Wisconsin ag engineer. Digman conducted an on-farm survey and a controlled study on mower overlap and found that losses varied from 0.5% to 16% and depended largely on just how attentive mower operators were.

Overlapping, when a mower is used at less than its full cutting width, wastes time and fuel, causes machinery wear and tear and isn't limited to smaller machines, Digman says.

The on-farm survey looked at pull-type, self-propelled and mounted (triple) mowers at operating speeds from 5.5 to 12.5 mph and working widths from 10' to 32' on 15 farms.

“We were able to look at the same fields with the same operators, the same machines, and with and without using the autosteer operation.”

He found that the mean overlap of machines that didn't have autosteer was about 5% — a number lower than he originally expected. Machines with auto guidance, however, showed half the amount of overlap loss, around 2.5%.

Mower width or speed didn't appear to impact overlap losses, but the type of machine may have, Digman adds.

“There were too many variables in the survey to control. We see that the pull-type machines might be a little bit higher (in losses) — that may be a trend. If we were to do a study and get all the machines side-by-side, we might be able to dig into this a little more.”

In the controlled study at the University of Wisconsin Arlington research station, he used a GPS with an RTK base station to measure overlap on a self-propelled windrower with a 14' cutting width. He wanted to find out if operating speeds and driver experience affected overlap loss rates.

“Our top operating speed was 8 mph (in the controlled study), and we saw machines out in the field going 12 mph. It would have been nice to get this operating speed range a bit higher to be more reflective of what is going on,” he says.

What he found was that driver attentiveness and speed affected mowing accuracy. “The drivers who were less attentive had more overlap as they drove faster.”

Driver fatigue may also affect loss rates and is another possible factor that Digman would like to study in future trials.

Economically, he says, cutting overlap losses in half by buying auto guidance equipment pays for harvesters who mow 500 or more acres “in really short order.”

But it will take more than a year for a grower with 100 acres cut four times in a year at a 5% overlap loss to pay for autosteer, he says.

“The economics are really going to depend on your situation, how many acres you are covering with a machine and what kind of driver you have.”