Boat Engines

Engine Types

Powered boats have one of three types of engines: outboard, inboard, and stern drive engines.

What Is an Outboard Engine?

Outboard engines are called “outboards” because they are mounted on the boat’s transom, outside of the boat’s hull.

Outboard motors are self-contained units that include the engine, gearbox, and propeller. These engines also control the steering. On smaller boats, a hand tiller is often used. On larger outboards, a steering wheel is used to adjust the engine’s direction.

What Is an Inboard Engine?

Inboard engines are four-stroke automotive engines that are located inside the boat’s hull. Inboard engines power a drive shaft that is connected to and moves a propeller.

Unlike outboards, inboard engines do not steer the boat. Inboard engines have a rudder or rudders located behind the propeller that are controlled by a steering wheel. Maintenance and repairs are more difficult and often more costly for an inboard engine than for an outboard engine.

What Is a Stern-Drive Engine?

Stern-drive engines are a combination of inboard and outboard engines. They are also called inboard/outboards (I/Os) because they shares features with both engine types. Stern-drive engines are similar to inboard engines in that they both use a four-stroke automotive engine that is mounted inside the hull.

Similar to outboard engines, stern-drive engines use a drive unit to steer the boat. Turning the steering wheel turns the drive unit, which determines the boat’s direction.

What Is a Jet-Drive Engine?

A jet-drive engine is a boat engine that uses water to steer the boat. The propeller is called an impeller and is housed inside of the engine. Water is pulled into the impeller and then forced out, which provides thrust for the boat.

Changing the direction of the water as it leaves the unit allows for steering. Jet-drive engines will lose some steering control at low speeds due to less water moving through the jet.

You should also read:

Boating Terminology

Parts of a Boat