Two motors are better than one…?
For a while, it looked like we were seeing the end of scrapers on civil projects. The availability of 50T mine trucks, and the lower running cost of articulated units, combined with a shrinking pool of experienced operators, were making scrapers something of a secondary consideration.
Nevertheless, good things tend to last and, in recent years, there has been renewed interest in using scrapers on civil projects. This is because people have realised their natural predator – the articulated dump truck – can be very inefficient. With articulated trucks, it’s far too easy for a good fleet to be split into multiple small fleets, causing relative loading rates to quickly exceed budget. Scrapers, in contrast, rarely suffer from this issue because they can’t slip into new cuts with the same ease as a truck. They suit operations where consistent workloads appear day after day, they load fast, they spread without needing another tool and they can traverse soft or slippery ground. In all, scrapers can be winners.
There is a ‘however’. If you are going to use scrapers, you need to figure out what sort of scraper you should use. There are some obvious considerations around size, availability and cost. However, one that commonly confuses those new to scrapers is whether they should try a single or twin power unit.
The second motor may not give the benefit you’re after
At first glance, it seems obvious. If one motor is good, then two must be great! But what does that second motor do for you? The reality is, it does not increase the scraper’s top speed, nor does it increase the payload. The second motor allows the scraper to accelerate harder up grades and gives improved retardation down grades. It can also improve loading rates in material that provides low friction, and allows the scraper to operate on steeper grades.
The choice between single or twin power units is an important one. Twin power units generally come into their own on steep grades and soft ground. Where you want to consider twin power units with caution is on:
Long flat grades – they quickly become non-viable and you’ll be effectively dragging around that extra motor and transmission for little gain once you’ve hit top speed
Resource-constrained projects – twin power units have double the features that can go wrong so if you are going to use them, ensure you have the resources to keep them going.
As with all earthworks strategies, plant selection has a critical role to play in setting up a project to achieve the right productivities at the right price and resource load. Know what matters to your specific project and match your fleet to those factors. More bang doesn’t always mean more buck.
