Choosing an inboard or outboard motor for your boat is simple once you are familiar with how your needs affect the decision. Inboard motors offer greater stability and are well suited to commercial, offshore, and certain water skiing applications, Outboards are general purpose and offer easy control, maintenance and replacement. There are no hard-and-fast rules, however, and personal preference will affect your decision.
Benefits of Outboards
If you spend a lot of time around working waterfronts, you might notice that the outboard engine is the default choice for fishermen and other light commercial inshore boats. Outboards are popular because their mounting position high up on the transom makes them easy to access and they can be tilted completely out of the water when not in use. When it comes to reliable service, many seasoned boaters find the outboard simply tough to beat.
Inboard/Outboard and Inboard Motors
That cute fibreglass runabout with the stern drive tucked under the swim platform is actually an inboard/outboard (I/O). The term inboard is reserved for motors mounted amidships that drive a propeller shaft that passes through the bottom of the hull. A true inboard system will rely on a separate rudder to enable steering. Inboards are popular both with slalom skiers because they produce little wake and with smaller fishing boats that work in heavy seas because of their low centre of gravity. An inboard system is required on heavy vessels requiring larger motors where the size and weight are not appropriate for mounting at the aft end of the hull. Inboards are less common in smaller recreational boats because they require a large box right in the middle of the boat to house the engine, are more costly to produce, and are more difficult to load on a trailer.
The power system you choose will have a direct effect on how you control your boat at low speeds. An outboard with its integral skeg and directional thrust enables effective manoeuvring with or without power. Where an I/O has a drawback is that it does not steer effectively unless thrust is applied, and docking can be more challenging as a result. The addition of joystick control to an I/O system simplifies docking, but it is not available on every model and at every price. Joystick control is also available for inboard systems from Volvo Marine's IPS system.
Outboard engines are perhaps the easiest to maintain. From inside the boat you can readily access the motor. On a trailer, the entire system is within easy reach. The factory engine housing is another benefit as it provides a fully integrated seal and protected environment for the engine electronics and mechanicals. An I/O has the motor located in the bilge of the boat where it is susceptible to water damage and moisture vapour. Access will sometimes be limited to a hatch in the floor. Inboard systems are similarly located in the bilge of the boat but larger boats will sometimes have sealed engine rooms with space to move about and storage for tools and spares.
The I/O May Be Best for You
The inboard/outboard configuration is very popular with recreational boaters and builders. With the motor tucked away at the stern, the rest of the boat is left open for seating. Designers like the I/O layout because it makes the transom easy to style, and it leaves room for a full width swim platform and additional amenities like showers and storage lockers. Small and midsized cruisers similarly benefit in that they will have more room below deck for accommodations. If you are in boating for the sheer fun of it and your needs are not too demanding, an I/O may be the best choice.