A donkey engine, or steam donkey, is a type of mechanical pulley system that was often used within the logging industry during the 1800s. Donkey engines were often steam powered, which made them highly efficient for transporting wood. In addition to being a popular fixture within the logging industry, these engines were also used for mining applications and maritime activities.
John Dolbeer is credited with inventing the donkey engine in 1881. The invention of the internal combustion engine during the mid-1850s largely eliminated the need for the steam powered donkey engine, but this logging machine was put to good use prior to the 1850s. Not only was this machine relatively easy to operate, it was also highly efficient at transporting large logs.
With the help of a work horse, a donkey engine cable was dragged into a wooded area where trees had recently been cut. Then, this cable was securely attached to a large log destined for a wood mill. When the cable was securely attached, a donkey engine operator would open the machine's regulator. This allowed the machine to act like a mechanical pulley by slowly pulling the log towards the machine. Once the log had reached the machine, the log was then loaded onto another vehicle. Eventually, all of the logs that were pulled out of the forest were sent to mills via rail.
Since donkey engines were large in size, and quite heavy, moving this type of machine proved to be a problem. Eventually, loggers learned that a donkey engine could move all by itself if the engine's cable was attached to a tree. By securing an engine's cable to a tree, the donkey engine would simply inch itself closer to the tree. Thus, the machine could be moved without a lot of manpower.
As sophisticated logging machines were created, the donkey engine was largely abandoned. In fact, many of these engines can still be found in forests all over the world. Since the machines were hard to move, even when the tree-pulling method was employed, many logging companies simply left donkey engines to waste away rather than remove them from a forest.
Some of these engines are presently on display in museums across the globe, though most of them have never been recovered. The modern logging industry has no use for donkey engines, since these engines are not as effective as modern machines. However, without the invention of the steam donkey, loggers who existed during the 1880s would have had a much harder life.