What it actually takes to mow a 22 degree slope: GPS data from a first cut

The block

Roughly one acre in Pullenvale. The ground runs from 18 to 30 degrees and averages 22. It carried heavy signal grass and had not been cut in a long while, which makes it a slashing job before it is a mowing job.

The machine was a Ventrac 4520P with the Tough Cut deck, cutting 1.7 metres wide. The job was GPS-logged from start to finish, so rather than describe it we can measure it.

What the GPS recorded

The machine spent 4.6 hours on the block and travelled 9.8 km in that time. It cleared around 6,600 square metres. That is an effective rate of roughly 1,400 square metres per hour, about a third of an acre.

One figure in the log matters more than the rest. Over those 9.8 km the machine climbed 645 metres in total, on ground with an elevation range of only 35 metres. The block is not 645 metres tall. The machine went up the same ground, over and over.

The downhill-only problem

In heavy growth at this gradient, cut grass mats under the deck and costs traction on the climb. The practical result is that large sections of the block could only be cut downhill. Every cutting pass was paid for with an empty return climb, and that is where the 645 metres came from.

The GPS puts a number on it. Every square metre of the block was covered roughly 2.5 times, measured at between 2.2 and 2.7 across three sessions. That factor, not the speed of the machine, is where the time goes.

Speed on the slope

The machine itself is not the constraint. Clean cutting passes ran at 4.4 to 5.3 km/ h. Comparing flat ground with the sections above 25 degrees, the penalty for gradient was only about 20 per cent. That part is the slope rating doing what it is sold to do.

The average speed across the whole job, including turns and repositioning, was 2 to 2.9 km/ h. The gap between those two figures is not the gradient. It is the coverage factor: time spent travelling over ground that has already been cut.

What this means for owners

Two things follow, and both matter more than the headline gradient.

The first is that a first cut through heavy growth costs roughly double a maintenance cut. The reason is not that the grass is longer. It is that on a maintained block the machine cuts in both directions, the empty return climb disappears, and the coverage factor collapses. The first visit is the expensive one. The maintenance cycle is where the saving is.

The second is about how the work is estimated. Time on this ground is driven by slope, growth, and the shape of the area far more than by raw acreage. A tight, scattered acre and one open acre are not the same job, and no per-acre rate tells them apart. That is why we estimate in days from a site walk rather than pricing by the acre.

If you are still working out which job your block needs, slashing versus mowing covers that choice.

Figures on this page are from our own GPS logs of the job described.