A trolling motor is a small engine affixed to the bow or stern of an angler's boat that provides a source of power for slowly trolling a lure or natural bait through water where fish are sought, or to allow for precision maneuvering of the boat so that the Angler can more effectively cast his bait to where the fish are located.

Trolling motors usually are electric powered, with a battery providing energy, but small internal combustion engines are sometimes used. Trolling motors are often used as an alternative to larger engines that propel fishing boats to and from preferred fishing areas. Trolling motors and their small propellers can usually be lifted, either manually or via an electronic system, from the water to reduce drag when the larger engine is used for propulsion.

Trolling motors are also commonly used as the primary source of propulsion for smaller water craft, such as canoes and kayaks. Additionally the electric varieties are well suited as a primary source of power for use on lakes where the use of a gas powered engine is prohibited.

The electric trolling motor was invented by O.G.Schmidt in 1934 in Fargo, North Dakota, when he took a starter motor from a Model A Ford, added a flexible shaft, and a propeller. Because his manufacturing company was near the Minnesota/North Dakota border, he decided to call the new company MinnKota. The company still is a major manufacturer of trolling motors.
http://en.wikipedia.org/wiki/Trolling_motor