Outboards vs. Inboard/Outboards: There's a Clear Winner

If you’re shopping for a boat, you may be given a choice - and it’s a pretty big one: Outboards… or Inboard-Outboards? This blog will go over each type of boat engine, their advantages, disadvantages, use-cases, and our ultimate recommendation.

Outboards

Starting with outboards, they are perhaps the most easily identifiable piece of machinery on a boat. They’re mounted to the transom of a boat and can vastly range in scale, from 2.5HP hand-controlled tillers to massive 600+ horsepower outboards with boating’s most advanced tech. As the name suggests, they sit outside of the boat and are clearly visible. They are available on virtually all recreational boats, including: pontoons, bass boats, deck boats, bowriders, and center consoles.

Outboard Pros

Outboards are designed specifically for boating, and this comes with a slew of advantages. Firstly, outboards are much more space efficient and compact. This gives you and your crew much, much more room and storage space.  

Outboard engines are light and powerful. Their compact design often requires less componentry and equipment than their I/O counterparts, which in turn allows for better performance at the same horsepower level. 

A massive advantage to outboards is their ease to work on. There are a few key reasons why they’re so much easier to work with, including:

Accessibility: Outboards are typically mounted on the transom of the boat, making them easily accessible from the rear. This accessibility simplifies maintenance tasks, such as checking the oil, changing spark plugs, or accessing the cooling system.

Portability: Outboards are self-contained units, which means they can be removed from the boat for service or repairs. The portability of smaller outboards makes it convenient to take the engine to a workshop if needed, reducing downtime on the water. Repowering is much easier for outboards as well.

User-Friendly Design: Outboard engines often have fewer systems interconnected, like exhaust or cooling systems, which reduces the chances of complex issues. They are also less prone to corrosive problems, as they are lifted out of the water when not in use.

Accessibility of Parts: Due to their popularity, outboard engines usually have readily available replacement parts and a well-established service network. As a result of this (and all of these points), service costs are often much cheaper for 

outboards! We’ll go over why I/O expenses are higher in just a bit.

Outboard Cons

Although they have a superior power-to-weight ratio, outboards don’t have enough torque for larger vessels. So - the workaround is to add another outboard, or two, or three, to get the required power! This can (of course) be costly.

Older outboard models are especially louder and less fuel efficient than newer models. This is an issue specific to older models, however - new outboards are much quieter and fuel efficient.

Of course, the outboard package is visible. Some boaters may prefer to have their engine compartment out of sight! Additionally, outboards take up a significant amount of space on your swim platform.

Inboard/Outboards

Inboard-outboards (aka I/Os or Sterndrives), on the other hand, rest inside of the boat - in a dedicated engine compartment. I/O engines use a marine-adapted automotive engine style. This engine operates a mechanism that looks and operates similar to the lower unit of an outboard. Most I/Os range from 10HP on the ultra low end, to some sailing over 1,000HP for some commercial engines! You’re mostly going to see I/Os on bowriders and mid-to-large cruisers. It’s incredibly rare to see them on anything other than that.  Some pontoon manufacturers have experimented with I/O ’s in the past in an effort to create some unique “clean transom” layouts, but seeing a new I/O in a pontoon is almost as rare as seeing a unicorn in your backyard!

Inboard/Outboards Pros

I/Os have greater bottom-end torque and good maneuverability on the water. Turning feels very responsive and on-the-dime. This is great for watersports applications - from skiing, to wakeboarding, and running around on the lake! In recent years, some newer drives come with forward-facing props which “pull” the boat through water instead of the traditional "push" style with the Mercruiser Bravo III and Volvo "Duo-props". This, coupled with the engine unit being tucked under the swim platform, allows for even more advanced wakesports!

Of course, you’re clearing up your back deck space significantly. Again, this is great for watersports, so you’ve got a clearer line of sight on who or what you’re pulling.

In terms of fuel efficiency and whether or not they are quieter, it depends on the engine. There’s no definitive answer for this point - but there are many I/Os that operate quietly and efficiently! Both modern I/Os and outboards are designed for an efficient, relatively-quiet ride that are huge improvements from previous renditions.

Inboard/Outboards Cons

The biggest downside of I/Os - and when I say biggest I’m not kidding - is their serviceability and the costs associated with that. This is due to a few reasons:

Location and Accessibility: I/O engines are located within the hull, making them harder to access. This requires disassembly of boat parts, adding both complexity and time to service.

Labor-Intensive: The confined space and complex configurations of I/O engines can make servicing labor-intensive, contributing to, of course, higher costs.

Corrosion and Saltwater Exposure: Constant exposure to saltwater can accelerate corrosion and wear on I/O engine components, leading to more frequent maintenance and potential repair costs.

Specialized Knowledge: Servicing I/O engines requires specific marine expertise, which can result in higher service rates from technicians with this specialized knowledge. In contrast, outboard service knowledge is more readily available and streamlined.

Total Loss: Unlike an outboard, a sterndrive requires you to cut a giant hole in the transom that sits below the water line. Bellows are essentially gaskets that prevent water intrusion - and if they fail, guess what? Your boat sinks.

Of course - all of these points equate to higher servicing costs and, often, more engine issues in the long run. 

Winterizing inboard-outboard engines is an essential maintenance step to protect them during the colder months. However, it comes with a notable disadvantage: the loss of access to your boat during winter. 

Limited Usage: Winterization typically involves draining the engine's cooling system, adding antifreeze, and taking other protective measures to prevent freezing and damage. These precautions effectively render the boat inoperable until it's de-winterized in the spring.

Seasonal Storage: To properly winterize most I/Os, the boat needs to be taken out of the water and stored for the winter season. This means you won't have access to your boat during the colder months, and if you decide to run your boat after winterization, you’d have to re-winterize it!

Extended Downtime: The duration of winterization can vary depending on your location and local climate, but it often means several months of downtime. This extended period without access to your boat can be frustrating, especially if you enjoy boating year-round.

Inconvenience: If you live in an area with unpredictable weather patterns, you may find yourself unable to use your boat even on unseasonably warm winter days due to the winterization process.

Cost: Of course - this is all a big inconvenience, and yes, another cost.

I/Os are on a downtrend. At the turn of the century, they used to dominate the market! But if we look at the past 20 years of search trends, I/Os have steadily declined in interest, whereas outboards are increasing. Additionally, future forecasts predict this margin widening - with outboards accounting for an increasing portion of recreational boating revenue.

This next point is a bit trickier. And that point is the price of I/Os versus outboards. A quick comparison will show you that I/Os are cheaper upfront than outboards! But it’s more complicated than that. Let’s look at Tahoe’s 210 model with an outboard and an I/O:

A base 210 S Limited (with a standard 225HP outboard engine) costs $56,240. The cost per horsepower is around $250.

A base 210 SI Limited (with the standard 250HP Alpha One I/O) costs $56,995 at about $227 per horsepower.

So - at first glance - it looks like I/Os are a better bang for your buck! But an important piece of consideration is that I/O horsepower is rated at the crankshaft, while outboard horsepower is rated at the prop. As the power from the crankshaft reaches the prop on an I/O, you lose about 15-20% of your power. So that 250HP ends up actually being around 200-215HP. Factor in the added weight of I/Os and the cost benefits quickly disappear. 

The Verdict

So - head to head, what do we recommend? Pretty easily - we choose outboards. Their reliability, comeuppance, ease of service, relatively low service costs, and compatibility with new technologies is unparalleled. Additionally, they have better mid-range acceleration and higher top speeds! That’s not to say that I/Os lose in every aspect, however! I/Os are good options for powersports, but their poor serviceability and associated costs are big flags.