Which is better, an outboard engine or an inboard engine? It’s one of the most debated questions amongst boaters, and each has a loyal following, with owners of both adamant that their choice is the best. But as with most things boating, the answer isn’t always clear cut, and while there are definitely pros and cons to both types of engines, ultimately it boils down to what kind of boat you want, where you plan to use it and how you want use it which will determine which is the best type for you. Here we take a look at exactly what characteristics inboard and outboard engines have, and what their advantages and disadvantages are.
What is an Outboard Motor?
An outboard engine is one which is fixed to the exterior of a boat at the transom. Popular on fishing boats, recreational boats and smaller boats such as RIBs, the outboard engine has an upper section, where the power head is located, the middle section (which is bolted to the transom) and the lower section. Depending on the size of the boat the engine might have a handle grip for steering, or larger boats such as center consoles might have up to four outboards as the power level wouldn’t otherwise be enough for larger vessels. Reliable and cost effective, outboards can be can be fully lifted out of the water which makes both maintenance easy and prevents corrosion making these hugely popular choices the world over.
What is an Inboard Motor?
In contrast to the outboard engine, and as the name implies, the inboard engine is essentially positioned inside the hull of the boat. It is comprised of two main components, the power head and the drive shaft, which is attached to the propeller. Found on larger boats, watersports boats and those which navigate more tumultuous seas, the inboard engine offers a quieter ride, more cabin space and better fuel efficiency, however their downsides are that maintenance is more difficult.
There are three kinds of inboard engines:
• True Inboard engine: With a true inboard engine, the propeller doesn’t steer the boat and it’s in a fixed position. A separate rudder controls the steering. True inboards are then further categorized as D-Drive inboards, where the engine is placed in the middle of the boat, and the V-Drive, where the engine is located at the back of the hull.
• Sterndrive (inboard-outboard engine or I/O): This is where the engine is bolted to the back of the boat (but fully concealed) but the drive system (propeller and rudder) goes through the transom of the boat and sticks out the back, essentially part inboard and part outboard. Popular on fishing boats where catching and deck space is important, or on watersports boats where a swim platform can be added without an outboard getting in the way.
• Jet Drive: This is an inboard engine that does not use a propeller propulsion system, but instead uses water to power the boat. Popular on small boats (especially Jet skis) and in shallow waters.
Differences between Inboard and Outboard Engines
When it comes to comparing inboard and outboard engines we have to look at a whole host of criteria. Ultimately, there is no best option, but a best option for your boat and your needs.
When it comes to which is more aesthetically pleasing it is, as with all things boating, purely subjective. Some love the powerful, meaty look of an outboard (or four) glimmering off the stern, while others prefer the sleek silhouette that you get with an inboard engine. Design-wise, swim platforms are possible but awkward with an outboard engine in the way.
These days there is very little in it when it comes to the fuel efficiency of an inboard engine and that of an outboard. However, while that’s true at face value, in practice the weight of your boat will determine how fuel efficient it is. A heavy boat using an outboard engine will have poor fuel efficiency, while an inboard would offer more power and therefore less fuel usage. Ultimately, the inboard engine is considered to be the most fuel efficient.
Performance-wise an inboard engine generally offers a smoother ride, especially in rough water conditions, as it sits deeper in the water because of the weight of the engine in its center. However, it’s this extra drag which also means that inboard engines don’t tend to offer the same top cruising speeds as outboards. When it comes to maneuverability, the inboard takes the medal.
Maintenance and Replacement
Maintenance is a big deciding factor when choosing between inboards and outboards, especially when it comes to saltwater boats. Where there’s salt, there’s corrosion, and so being able to easily access the engine for maintenance and cleaning, as well as being able to lift it completely out of the water and store it throughout winter means the outboard is the clear winner here. Inboard engines are harder to access, and are bolted inside the hull of the boat, meaning they are more susceptible to corrosion. Having said that, outboard engines are exposed to the weather and elements, meaning they require more maintenance to keep them in good condition.
When it comes time to replace your engine, it is perhaps no surprise that outboard engines are easier to replace, as they simply unbolt from the boat. In turn, inboards require the boat to be lifted out of the water and it involves a much more complex engineering procedure to replace them.
When it comes to safety, one of the biggest risks with an inboard engine is hitting submerged obstacles as it can’t be raised the same way as an outboard can. Having said that, inboard engines have in the past been more associated with onboard fires than outboards, and as such insurance companies can often charge more.
Differently to the past, both outboard and inboard engines are equally reliable these days. However, inboard engines are able to navigate a boat through much more challenging sea conditions than an outboard can, ultimately making it the most reliable. So ultimately, it depends on what you want to use your boat for when it comes to the question of reliability.
In general inboard engines tend to cost more to buy new than outboard engines, and when choosing your boat you’ll find huge price differences between the same models with different sized engines. However, an inboard engine is likely to last longer and not need to be replaced as soon as an outboard engine.
The Boating Experience
The overall boating experience plays a role too in deciding which engine to get. If you’re looking for a quiet cruising experience with a drive akin to driving a car then the inboard wins hands down, as outboard engines are much louder. On the other hand, outboards can be raised in shallow waters whereas inboards can’t be raised, meaning adventures in shallow coastal areas, lakes, mangroves or rivers are best with an outboard. While swim platforms are possible with outboard engines, they’re cumbersome and awkward, whereas wide platforms on boats with inboards are very common.
Advantages and Disadvantages of Outboard and Inboard Engines
Advantages of Outboard Engines
• Easier to perform maintenance on
• Lower maintenance cost
• Can be raised out of the water in shallow conditions
• Can be removed and stored during winter
Disadvantages of Outboard Engines
• Less fuel efficient
• Can’t have a large swim platform
• Always visible
• Generally have less longevity than an outboard
Advantages of Inboard Engines
• More fuel efficient
• Can accommodate a swim platform
• Smooth, car-like driving experience
• Are fitted in the boat and therefore more aesthetically pleasing
• More reliable in rough sea conditions
Disadvantages of Inboard Engines
• Takes up more internal space in the boat
• Not easy to maintain yourself
• More expensive to maintain/replace
• Can’t be used in shallow waters
• Can’t be removed and stored in winter
What Boats Usually Have an Inboard Engine?
You will usually see inboard engines on large boats, bowriders, ski boats and medium to large cruisers. They offer more seating, can have swim platforms and are better geared to watersports as they create a more suitable wake. Any boats navigating open oceans or rough conditions will tend to have inboard engines too, as these are the most reliable. While almost any boat can have an inboard or sterndrive engine, it is rare to see them on certain styles of boats including small RIBs, Jon boats, pontoon boats and bass boats.
Photo credit: Chaparral Boats
What Boats Usually Have an Outboard Engine?
As we’ve just seen, it is common to have outboard engines on smaller boats such as small RIBs, Jon boats, pontoon boats and bass boats because the weight to power ratios work best. Having said that, large center consoles, fishing boats and some large RIBs can have up to four outboards to provide sufficient power and speed.
Photo credit: Valhalla Boatworks
What are Popular Brands of Inboard and Outboard Engines?
Inboards and outboards are very different, not just in their placement but in their engineering. Technology is changing quickly and there are more and more hybrid engines hitting the market these days (offering a combination of electric power and combustion engine), however some of the most reputable brands of outboard engine manufacturers include Suzuki, Mercury, Honda, Yamaha and Evinrude. Popular brands of inboard engine manufacturers include Scania, Volvo, Mercury Mercruiser, Beta Marine and Aquamot.
And the Winner is…
As with many things boating, there is not a clear winner and ultimately the size and style of your boat, as well as what you want to use it for, where you plan to store it and the conditions you want to use it in will decide whether an outboard engine or inboard engine is the best choice for you.
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