Most people may have usually come across a boat motor while out boating or fishing. Installed at the rear of the boat, a boat motor is a self-contained unit with an engine, a propeller and other subsidiary systems. The motor is designed to pivot over the mounting, enabling it to steer the boat. The motor has its transmission leg in the water, which acts as a rudder when the propeller is not in power. When the boat is cutting its way through shallow waters, the unit can be retracted to prevent it from getting entangled with seaweeds or other obstructions. Depending on the power required, boat motors are available in different powers. Motors can be two stroke, three stroke or four stroke; the higher the number, the lighter is the unit. Four stroke engines are mainly for low-end light boats that are very fuel efficient and carry a limited number of people. Two-stroke, on the other hand, may not be as fuel efficient, but are packed with high power and performance. Dinghies and small fishing boats generally have small outboard units that can even be detached. Big vessels involved in activities like trolling have huge outboard units that are generally electric and not fuel run. Boat motor does not need cooling fans or radiators for cooling the engine when it heats up. There is an inlet to supply cold water, of which there is no scarcity while sailing. When this water gets heated up, it can be let out and refilled with cold water. British Seagull, Evinrude/Johnson, Honda, Mercury/Mariner, Nissan, Suzuki, Tohatsu and Yamaha Motor Corporation manufacture boat motors.