The Donkey Engine

Of course the donkey engine was not restricted to working with timber, they were put to great use anywhere that portable steam driven pulling power was needed. They were common in mines, wharves, and railroad locations. The engine shown at left was found in July 2001 at the North Star Mining Museum in Nevada County California USA. According to the museum the engine had been used for both logging and mining. Initially it was used to obtain the timber to line the mine shafts, then used for mineshaft hoisting duty. In all probability it is likely that the engine alternated between these two and possibly other tasks. Despite being stored outside the engine appears to be in great shape and barring boiler damage would probably be an easy restoration. At present the museum have preserved the unit with an eye to making it operational in the future.

These two pictures show donkey engines at work in the woods doing what they do best, hauling timber. The engine at left is working an arial tramway where logs are hoisted high into the air at the crown level of the trees then "flown" along a wire towards the donkey engine usually situated near some other form of transport such as a railroad or river. The engine at right is performing dragging duties where it hauls the log along the ground either to hand it off to another donkey situated somewhere else or some other form of transportation. Donkey engines were generally not used to haul timber to the actual mill except while the area around the mill is being cleared.

The drawings below are from the Dolbeer Logging Engine patent mentioned earlier. They show how simple and flimsy the initial version of the engine was compared to the later units in use in the woods. More interestingly the second drawing shows John Dolbeer's recommended method of fixing the engine to allow it to perform its various duties without drawing the engine towards the work instead of the work towards the engine.

Looking at the patent image, it can be seen that the initial version only had the winding capstans but did not have a winch drum. This would have reduced its usefulness on the crane front and also made it harder to use with wire rope suggesting it was more likely designed with hemp rope in mind. Later versions with the winching drump lend themselves to wire rope (cable) much more readily. It should be noted that the choice of vertical fire tube boiler is extremely logical given the circumstances in which the engine would be expected to operate. There is very little flat ground in the mountains and having to dig a flat platform into the ground or build one up above the ground to operate the engine would have been infeasible. The vertical boiler would also allow the unit to use its own power to drag itself through the forest simply by attaching its rope to a near where the operator wanted the engine to go. A horizontal boiler would not be up to working under the extreme operational angles as the water would end up one end of the boiler either directly over the fire or away from it (exposing the crown sheet leading to boiler failure).

This image shows how the unit was to be secured to keep it steady and prevent it from dragging itself through the forest instead of dragging its load. It appears to demonstrate a method for dragging a very long load towards itself using two ropes simultaneously. Cleverly, the engine is actually facing away from the load, meaning that the pulleys shown affixed to the two stumps set the angle of attack. This would minimise moving of the engine in relation to the load it is expected to pull. This would allow quick "reloads" with only the time to spool the rope out to the site of the next load impacting efficiency.

John Dolbeer's invention is credited with opening up more areas to logging previously inaccessible to the loggers as they had no way to get the felled logs out. While the units pictured are all within the USA they do exist within Australia in similar capacities.
The following images show a maritime use of a donkey engine built by Clyde Iron Works Minnisota USA. The boiler is G2021 and is a 100 psi boiler the engine is No. 2863 and is a two piston donkey engine with dual winding drums. Attached to this engine is another winding engine, I guess you could say it is a donkey's donkey? The second engine was used on a pier locally in San Francisco and has been piped to the clyde boiler to demonstrate it.

John A Taubeneck wrote to me with some additional information about this machine:

I was looking at your web site and noticed the photos of Clyde donkey #2863. I have copies of all of the Clyde construction records from 1908 to 1927 so I looked up this machine. Here is what was said:

#2863 7X10 2 drum Contractors Hoist 42X90" boiler Shipping Weight 10,950 lbs Tested March 12, 1917 Shipped March 20, 1917 to Portland Oregon via Clyde Equipment Co. Seattle, Washington

There is a list of California Donkeys prepared by John A. Taubeneck.