Design and Usage
Steam donkeys acquired their name from their origin in sailing ships, where the "donkey" engine was typically a small secondary engine used to load and unload cargo and raise the larger sails with small crews, or to power pumps. They were classified by their cylinder type – simplex (single-acting cylinder), or duplex (a compound engine); by their connection to the winches (or "drums") – triple-drum, double-drum, etc.; and by their different uses: high-lead yarder, ground-lead yarder, loader, snubber, incline hoist, etc. A good deal of the cable-logging terminology derived from 19th century merchant sailing, as much of the early technology originated from that industry.
A logging engine comprised at least one powered winch around which was wound hemp rope or (later) steel cable. They were usually fitted with a boiler, and usually equipped with skids, or sleds made from logs, to aid them during transit from one "setting" to the next. The larger steam donkeys often had a "donkey house" (a makeshift shelter for the crew) built either on the skids or as a separate structure. Usually a water tank, and sometimes a fuel oil tank was mounted on the back of the sled. In rare cases, steam donkeys were also mounted on wheels. Later steam donkeys were built with multiple horizontally-mounted drums/spools, on which were wound heavy steel cable instead of the original rope.
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