What is donkey engines?

Donkey engines are small engines used to power auxiliary equipment on ships, or to pull barges or rafts. They are typically steam-powered, and were introduced in the 19th century as ships grew larger and required more power. Donkey engines were also used in mining and logging operations to power equipment. In modern times, diesel engines have largely replaced steam-powered donkey engines. The term "donkey engine" is believed to have originated from the mule-like noise made by the engines.