Inboard Vs. Outboard Motor: What Are the Differences, and Which is Better?

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When it comes to boats, there are a lot of technical things you have to look into. From the size of the boat to the best fishing spots, opinions can vary greatly. Inboard vs outboard motor is a frequent debate among the boater community. So what are the difference between the inboard and outboard motors? 

You don’t exactly need an engineering degree to know which one is better. If you know the pros and cons of each type, you would be able to judge better which one is more suited for you. After all, when it comes to boats, technical details aside, you have to listen to your gut. 

But before you listen to your gut, let’s just look at why this choice is so important and what each of them offers.

Understanding Boat Motors

If you just walk down your local watering hole and ask some boat owners the same question, you will get multiple answers. Their answers, even though conflicted, are not all wrong. The thing is there is no easy way to answer whether the inboard motor is better than the outboard. 

Boats use engines or motors to run. Motors are powered by electricity, whereas engines are powered by fuel. It can be confusing at times to determine whether a boat is equipped with a motor or an engine. This is because boaters often use the terms interchangeably.

The motor is what moves the boat on the water. So you can guess how important a motor is for a boat. It’s just like the engine of your car, except it is designed to be suitable for marine conditions. 

When buying a boat, you can start by finding the correct size of the motor that will allow you to maximize your boat’s performance. Furthermore, the weight and the horsepower of the engine holds the same level of importance. Hence, deciding on the make, type, and manufacturer of the motor will be important decisions. 

Inboard Motors

An inboard motor or engine is the one located inside the boat. Just how your car engine moves the wheels, the inboard motor moves a different type of wheel. This is the propeller which runs the boat. 

The motor has a powerhead that is attached to a drive shaft. This shaft is essentially part of a drive system that runs the propeller. The propeller can drive the motor forward or backward. The boat’s operator uses the drive system to control the boat. 

This motor is bolted in the middle of the boat or at the back. Since it’s on the boat, hence the name inboard motor. Even within the inboard category, you have an option to choose from different types. 

In order to better compare it with the outboard engine, we have to look at the different types.

Types of Inboard Motors

The distinguishing part between the different inboard motors is the drive system. Even though boaters use the general term inboard motor for virtually all of them, they are quite different in terms of performance. 

Here are the three types of inboard boat motors:

True Inboard

The True Inboard motor or engine uses two types of drive systems. When we say the system, we mean the drive shaft, propeller, and engine all included. So the two drive systems are D-Drive (Direct Drive) and V-Drive.

In the D-Drive, the engine is in the middle of the boat. The shaft is coming out the back of the engine. It uses a transmission system that engages the shaft into the water, with the propeller at the end of it. 

The V-Drive is the true inboard placed on the back of the boat. The difference is that the shaft is coming out of the front of the engine. The transmission on this has V-shape, with the other end of the shaft heading out at the bottom of the boat. The propeller is at the end of the shaft. 

The transmission is inside the boat in both the drive systems. The rudder behind the propeller changes the direction of the boat. 

Inboard/Outboard (I/O) or Sterndrives

This type of inboard engine is placed at the back of the boat. The drive system on sterndrive goes through the transom of the boat. This system consists of two parts: the upper unit and the lower unit. 

These two units are essentially the transmission of the engine. The upper unit is responsible for changing the spinning motion from vertical to horizontal. This spinning motion goes to the lower unit, and the unit spins the propeller in a clockwise or counterclockwise rotation. 

What makes this system different is that it does not have a rudder. Since the entire drive system can turn left or right, there is no need for a rudder. Additionally, it can trim the drive system up. As a result, more of the boat is above water, which allows for higher speed. 

You can read more about the differences here

Jet Drive

This is completely different from the other two types. However, it’s still a type of inboard engine because it’s found inside the boat. It uses water from under the boat and uses an impeller to create a jet. 

When the water comes out forcibly, it pushes the boat. It’s basically how a jet ski operates. The principle is followed on a boat, much bigger than a jet ski. 

This type of system is not as common as the other two. However, it’s gradually making its way thanks to technological advancements. It can deliver quite high speeds for a lightweight boat. However, it does utilize a lot of power. 

Pros & Cons of Inboard Motor

To make it easier for you to understand the inboard motor, here is the detailed look into the limitations and benefits it offers.

Pros

The biggest advantage of an inboard engine is its drive system. The engine is hidden, which keeps it protected from moisture, dust, and water. Since it’s hidden, it does not show, and the boat’s overall appearance is a lot cleaner.

Inboard motors are generally high-quality, and therefore long-lasting. These engines use diesel, which has a longer life. On sailboats, a diesel engine can run up to 30 years. This is why these are more expensive too. 

With the engine inside and in the middle, the boat is more stable. You do not have to worry about losing the balance of the boat. In smaller boats with the engine on the outside, balance can be a problem for a beginner. 

Cons

A boat with an inboard motor will cost. However, given that the maintenance is low, it will not cost you a lot of money in terms of maintenance. 

Another disadvantage of an inboard motor is that it acquires space on the boat. This leaves little room for the interior of the boat. This is not such a significant problem with bigger boats, but with smaller boat space can be an issue. 

Lastly, repairing these can be a nightmare. Since the engine is hidden in the hull, cutting through it is a hassle. Even when you do get to it, there is not much room to work on it. 

Outboard Motors

Outboard motors are bolted to the transom of the boat and located entirely on the exterior of the boat. They are a self-contained package containing everything, including engine, propeller, cooling system, and gearcase. 

The powerhead is at the top section while the middle section attaches to the boat. The lower section is the drive system. Two-stroke engines are the most common for outboard boats. These use oil for lubrication as well as fuel.

Many newer boats are using a four-stroke design. Even the ones with two-stroke are using direct-injection that is cleaner in terms of fuel burning. You steer the outboard boat by tiller or steering wheel that makes the entire engine swivel. 

Outboard motors are a huge market. These are generally more popular for fishing and recreational boats. It’s a lot easier to handle. Replacing it is also easier as it’s on the exterior of the boat. 

Pros & Cons of Outboard Motor

Here is a quick look into the pros and cons associated with an outboard motor.

Pros

The small size and portability of an outboard motor make it ideal for some boats. You can easily remove it when it’s time for repairs, and you can tilt the entire engine to maneuver the boat. 

You can trim the boat up, so it does not hit the bottom of the water. So this makes this motor ideal for saltwater. 

It can also deliver good speed, especially for a small boat. Since it’s on the exterior of the boat, you have more space on the inside of the boat. 

Its main advantage is its low cost. Even though you will have to replace it sooner, the overall cost would not be so high. 

Cons

The disadvantage of an outboard motor is that its visible. If you’re all about the looks of the boat, an engine stuck outside the boat is not the most appealing look. 

Also, there are some safety hazards. If the fuel tank is not placed properly, it can prove dangerous. Similarly, if the engine size does not fit well with the weight of the boat, it can become unbalanced and can tip over. 

This kind of boat engine does not have a high power to weight ratio. Simply put, it does not have enough torque to withstand a lot of cargo. You can add more motors, but that will be a lot of work, not to mention additional costs. 

Inboard Vs. Outboard Motor: Comparison

Now you know what each type of motor is and what its pros and cons are. It’s time to compare the two directly. This will help you compare the two kinds of motors in different aspects. At the end of the day, it will boil down to your own boating needs. 

  • Cost

Inboard motors are way more costly in comparison with outboard motors. The one-time purchasing cost for outboard motors is low. However, it does incur maintenance and replacement cost. 

An inboard motor can give you 1500 hours, while an outboard motor will give you 750-900 hours. After these hours, you will have to complete the required maintenance for the engine. Inboard motors generally last longer, so you will not have to replace one anytime soon. 

You should also factor in insurance costs. Since inboard motors are more expensive, their insurance is costlier too. 

  • Maintenance

Aside from the one-time buying cost, you also have to consider maintenance costs. Generally, inboard motors have higher maintenance costs as compared with outboard motors. However, the low frequency of maintenance or repairs offsets this cost.

Sterndrives are most expensive to fix as the engine is placed in an enclosed space. Outboard motors may be cheaper to repair and maintain, but they do not have a life as long as their inboard counterparts. You can do small repairs by yourself to save money.

Inboard boats are also susceptible to issues because of their positioning. They can be difficult to open because of a small hatch in the housing. Once you open, water and moisture can cause damage. 

  • Water Activity 

The water terrain you take your boat on influences the life of your boat. Saltwater is corrosive for most materials present in the boat and engine. However, you can prevent it by trimming the engine off the water.

The outboard wins the race here, as it is easy to maintain and trim. Whereas, an inboard system is left out in the water for the corrosion to grow. Even though the hull protects the engine, it eventually needs repair, which is expensive for inboards. 

  • Safety

When it comes to safety, the discussion is quite straightforward. The design of inboards makes them safer than outboards. As the fuel tank is secure inside the hull its less likely to get damage, leak, or burst. However, if you design the boat better, you can prevent this from happening in an outboard. 

  • Fuel Economy

Today’s boat engines are a lot more efficient in terms of fuel consumption. With climate change becoming a major threat, companies are moving towards even better engines that produce less carbon footprint. This essentially requires less fuel usage. 

If we simply compare numbers, then the outboard motors offer a better fuel economy. This is simply an advantage because of their low weight and faster speeds. But in terms of weight to power ratio, the inboard comes out on top. 

Fuel economy is very subjective and may vary by the particular motor model, whether it’s inboard or outboard. Generally, the older the motor is, the higher its fuel consumption gets. Also, If there is a lot of weight on board, it will consume more fuel. 

  • Power

Inboard motors’ directional thrust and integral skeg make them easy to maneuver at low speed. As a result, it’s easier to dock such boats. The opposite is the case with outboard motors. 

The outboard motor needs thrust to steer. So you need more power to maneuver it. But more power is not ideal when you have a small boat. 

Which One Should You Choose?

If you’re confused about whether you should go for inboard or outboard motor, just evaluate your purpose. You can weigh the pros of each against one another in the context of your boating needs. 

Inboard motor may have more pros, but in some cases, the outboard motor is better. For smaller boats, the outboard motor is better. It can deliver the speed you need. It will keep the engine out of water when you trim it. Also, it will not cost you a fortune. 

For bigger boats that you use quite often, especially if using commercially, an indoor motor would be the right choice. It will deliver the performance you need. Also, you can put more cargo and people on the board. Most importantly, it would not wear down so easily. 

Most experts say that inboard motors are more reliable. However, that is changing now. Outboard motor manufacturers are producing high-quality motors that are cutting in close in terms of reliability. Yes, you will make repairs often, but the motor will last longer.

Another important and perhaps deciding consideration is your budget. Are you a serious boater who does not have any budget restrictions? Are you an occasional angler who does not have a big budget? This should help you make a decision too. 

In case you didn’t know, you can convert an inboard into an outboard too. You will need to hire a professional to do that for you. 

Conclusion

This is just a broad description of each type of boat motor. When buying a boat or just the motor, you have to focus on the exact model. Research thoroughly about that particular engine. When you decide which one you want, you can start looking for the best one you can get within your budget. 

With time you will learn things yourself. Whether you’re buying a boat for fishing or just going out on the lake or sea, it would not matter so much once you’re on the water. Nevertheless, always prioritize safety. You do not want to compromise on safety and quality.