Runabout Boat Engines: What's Under The Hood?

Runabout boats are small motorboats that can hold between four and eight people and are well-suited to a variety of activities on the water. They are typically powered by sterndrive or outboard engines, but can also be powered by inboard engines or jet drives. Runabouts are popular due to their low cost, ease of maintenance, and versatility. They are not designed for a specific purpose, but their maneuverability makes them a preferred choice for casual boat enthusiasts.

Runabout boats can be powered by inboard engines

Runabout boats are small motorboats that can accommodate four to eight people. They are usually designed for all-around use and are easy to manoeuvre, making them a popular choice for casual boaters. Runabouts can be powered by inboard engines, which are mounted within the hull of the boat.

Inboard engines have the engine block permanently fixed inside the hull, with a drive shaft and a propeller underneath to drive the boat forward. A separate rudder is used to steer. This is in contrast to outboard engines, which are external motors that combine the engine, gears and propeller in one unit, and are mounted on the transom (back) of the boat.

Inboard engines have several advantages. They are similar to automotive engines, so people who are used to working on cars will find them familiar and easy to maintain. Inboard engines also allow for a large swim platform to be attached to the transom, and a sunpad to be placed on top of the motor box.

However, in recent years, modern outboard engines have become more popular. These tend to be cheaper, more reliable, and quieter than inboard engines.

As well as inboard and outboard engines, runabouts can also be powered by jet drives or inboard-outboard (stern drive) engines.

They can also be powered by outboard engines

Runabout boats are small motorboats that can accommodate four to eight people. They are usually powered by sterndrive or outboard engines, but can also be powered by outboard motors.

Outboard motors are steerable external drive motors that contain the engine block, linkage gears, and propeller within a single unit. They are mounted to the transom and steered by a remote system connected to a wheel mounted on the boat's console. Modern four-stroke outboard motors are gaining popularity due to their exceptional reliability, quiet operation, and smooth performance. They also tend to be more affordable than sterndrive options.

The first runabout boats, which date back to the 1920s, were designed to take advantage of the power of outboard motors. The introduction of the first Evinrude outboard motor in 1909 played a significant role in the development of these boats.

Today, outboard engines remain a popular choice for runabout boats. They offer advantages in terms of cost, reliability, and performance, making them a preferred option for many boat owners.

Or, you could opt for a hybrid inboard-outboard engine

Runabouts are small motorboats that can accommodate between four and eight people. They are usually used for pleasure activities such as boating, fishing, and water skiing. They can be powered by inboard engines, outboards, jet drives, or inboard-outboard (I/O) drives. Inboard-outboard drives are a hybrid, with an engine block mounted within the hull, linked to a pivotable lower drive unit that steers the craft, similar to an outboard motor.

Benefits of a Hybrid Inboard-Outboard Engine

A hybrid inboard-outboard engine combines the benefits of both types of engines. The inboard engine is easy to work on and maintain as it is similar to an automotive engine. It also allows for a large swim platform and a sunpad atop the motor box. The outboard engine is steerable and more powerful, making it ideal for larger boats.

Downsides of a Hybrid Inboard-Outboard Engine

However, there are also some downsides to a hybrid inboard-outboard engine. The inboard engine may require more maintenance, especially in cold climates where the cooling system needs to be flushed with antifreeze. The outboard engine, on the other hand, is easier to service since it is located outside the boat.

Hybrid Electric Propulsion

Another option for runabout boat engines is hybrid electric propulsion, which combines electric and fuel-powered sources. This system offers a clean, powerful, and silent motor with the familiar thrust of a traditional engine. The electric motor can be used for peaceful cruising, while the combustion motor can provide more power when needed. Electric sailing is also more comfortable due to the lack of vibration from a combustion engine.

Factors to Consider

When choosing between a hybrid inboard-outboard engine and other options, it's important to consider factors such as cost, maintenance, performance, and intended use. Inboard-outboard engines may be more expensive and require more maintenance, but they offer better performance and are suitable for a wide range of activities. Ultimately, the decision depends on your specific needs and preferences.

Jet drives are another option for runabout boats

Jet drives are used in everything from personal watercrafts (PWCs) to runabouts and commercial ferry boats. They are versatile, perform well in shallow draft applications, and can use reverse thrust as a braking system. However, they do not perform well in low-speed environments and are not suitable for applications where torque is more important than horsepower.

A jet drive uses an impeller instead of a propeller to move water and create forward thrust. The impeller is enclosed inside a pump cavity, which, along with the stator vane, increases the efficiency of the system by focusing the energy of the thrust. This is why jet drives have such great off-idle acceleration.

When considering a jet drive system, it is important to keep in mind that they do not have a true neutral gear. This is because the impeller is connected directly to the engine, so when the engine is running, the impeller is moving. Engineers have worked around this issue by creating a neutral setting that employs a combination of forward and reverse thrust.

Another drawback of jet drives is that they need thrust to steer. This means that if you chop the throttle, the boat will not steer. Some manufacturers have made rudders that mount to the bottom of the jet nozzle to improve steering off-throttle.

Engine type will depend on the boat's purpose, e.g. watersports or cruising

The engine type for a runabout boat depends on its purpose. Runabouts are small motorboats that can hold between four and eight people and are used for pleasure activities like boating, fishing, and waterskiing. They are also used as ship tenders for larger vessels or in racing.

If you are using a runabout boat for watersports, an inboard engine is a good option. Inboard engines are mounted inside the hull and are preferred for watersports due to their predictable wake. They are also used on vessels where more horsepower and torque are needed. Inboard engines are four-stroke automotive engines that have been modified for use on the water. They power a drive shaft connected to a propeller, with a separate rudder for steering.

If you are using a runabout boat for cruising, you might prefer an outboard engine. Outboard engines are mounted outside the hull and are known for their agility and ability to power smaller boats efficiently. They are steerable external drive motors containing the engine block, linkage gears, and propeller within a single unit, taking the place of a rudder. Outboard drives are mounted to the transom and steered by a remote system leading to a wheel mounted on the boat's console.

Another option for a runabout boat is a sterndrive engine, which combines features of both outboard and inboard engines. Sterndrives provide the power and torque needed for pleasure boats, with the added benefit of agility in manoeuvring and docking. They are mounted inside the hull and attached through the transom to a drive unit that resembles the lower gearcase portion of an outboard.

Finally, a jet drive engine uses water to propel and steer the boat, offering high performance and safety benefits in shallow waters due to the absence of exposed propeller blades. Jet drive engines are commonly used for personal watercraft, but many boats also feature jet propulsion systems.

Frequently asked questions