Difference Between Inboard And Outboard Boat Motors

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For the uninitiated, there is no difference between an outboard and an inboard engine. They simply believe that you can use any of these engines as long as they propel the boat forward.

Outboard engines have an appealing look and make the boat look “sexier” and for this reason, people tend to use these on their boats.

If someone has a large boat, the preference seems to be to add two outboard engines, to propel the huge boat, rather than have an inboard engine.

What is the difference between an inboard and outboard motor? An inboard motor is permanently placed inside the boat and helps power a prop shaft through the hull. An outboard motor is placed outside the boat, generally hung by clamps at the stern of the boat.

We'll have a look at images below to help illustrate this more visually.

From an engineering point of view, the tiny propellers on an outboard engine, even a pair, would never generate enough grip on the water of a large diameter wheel on the inboard shaft driven by a classic electronic common-rail.

As a result, the outboards end up using more fuel, ruin the balance of the boat and may eventually blow up as they try to propel a huge hull.So what is the true difference between an outboard and an inboard engine?

What are their performance parameters and which is suited to large or small sized boats?

This article will go through several aspects of outboard versus inboard engines so you can make the right decision when choosing an engine for your boat.

Before delving deeper into the nitty gritty of these two types of engines, you must first know the difference between an engine and a motor.

·        Boat Engine – this is a combustion engine, which uses diesel fuel to generate energy to propel the boat forward.
·       Boat Motor – this uses electrical energy, such as a battery, to generate the required power to propel the boat forward.

These terms are generally used interchangeably, but it is good to know the basic difference between an engine and a motor.

Some boats use a combination of both; this is found on big boats, ships, and even submarines, which can easily switch from fuel engine to  electric motor to turn the propeller.

Well, let us not digress. What is the true meaning of an inboard and outboard engine?

This article covers everything in dept.

  • Inboard Motor Defined
  • Outboard Motor Defined
  • Inboard & Outboard Motors (Aesthetics,Performance and Safety)
  • Inboard & Outboard (Saltwater Problems)
  • Inboard & Outboard Motors (Fuel Economy)
  • Inboard & Outboard Motors (Maintenance)
  • Are inboard motors bad?
  • Advantages Of Outboard Motors
  • Inboard & Outboard Motors (Highlights)
  • Examples of Outboard Motor Boats
  • Examples of Inboard Motor Boats

Inboard Motor

In basic terms, an inboard engine is that which is placed INSIDE the hull of the boat. It is made up of two main parts.

The first is the power head, which is much similar to the engine of a car. In fact, there have been instances where a car engine is removed, and after minor changes, is used to drive a boat.

The second is the drive shaft, which is the metal shaft that is attached to the propeller.These two work together to propel the boat forward.

This may seem to be quite straight forward,right?

Well, there are three different kinds of Inboard engines:

·        The true inboard engine
·        The inboard/outboard engine(also known as I/Os or Stern drives)
·        The jet drive

THE TRUE INBOARD ENGINE

A true inboard engine is that which is fully placed in the hull of the boat. However, the true inboard engine can further be divided into two categories depending on where it is placed within the hull of the boat.

1.             The D-Drive
– This is the engine that is placed in the middle of the boat, and the propeller is directly at the end of the drive shaft.

inboard motor

Image courtesy of Used Boat Warehouse

2.             The V-Drive – This is the engine that is placed at the back of the boat, with the shaft creating a“V” shape so that it comes to the propellers at the back of the boat. Think ofthis as a bend, like you would bend your arm at the elbow to rub your nose.

difference between inboard and outboard motors

Image courtesy of Used Boat Warehouse

The direction of the transmission is the one that determines whether the boat moves forward or backwards.
There is a rudder placed behind the propellers, which changes the direction of the water flowing from the propeller in order to steer right or left.

THE INBOARD/OUTBOARD ENGINE (STERN DRIVE)

inboard/outboard engine

Image courtesy of Used Boat Warehouse

This is the engine that is bolted to the back of the boat with the drive system going through the transom of the boat.

The drive system is made up of two parts,the upper and lower units.The upper unit changes the spinning motion of the engine from horizontal to vertical, and this enables you to propel the boat forwards (horizontal) and backwards (vertical), as the motion is transferred to the lower unit.

To explain further change of orientation from horizontal to vertical changes the spinning motion of the driveshaft in the lower unit to change the spin of the propeller from clockwise to counterclockwise, hence the change from forward propulsion to backwards.

The I/O engine has the ability to turn the full drive system from left to right, allowing you to change the direction of the boat. This is why the I/O engine does not have a ruder like the true inboard engine.

The I/O engine also has the ability to change its trim, allowing you to lift the hull out of the water and thereby increase the speed of the boat.

A true inboard engine cannot adjust the trim.Before we leave the I/O engine, let’s talk about the Pods

What is a Pod?

This is an I/O engine but it is not a stern drive. Why?The stern drive is attached to the transom of the boat, whereas a pod is attached to the bottom of the boat.It is as simple as that.

Okay, now we can move to the final type of inboard engine.

THE JET DRIVE

jet drive inboard engine

Image courtesy of Boaterrific

This is an inboard engine that does not depend on the propeller propulsion system, but instead uses water to power the boat forward.

The engine “sucks” up water from beneath the boat, and then pushes it forcefully out the back, using an impeller.

The jet of water then moves the boat forward. In reverse, it sucks water from the back, and pushes it out the bottom, allowing you to move the boat backwards.

The jet drive is great for small boats and it suitable for super shallow waters.

However, it does not work very well on large boats since it cannot generate enough power.One of the most common uses of the jet drive is on the super-fast jet skis.

Inboard engines, just like car engines, get very hot and require a cooling system. Here is a look at the cooling systems of inboard engines.


Inboard engine cooling systems

There are two main coloring systems for inboard engines.

i)                   Closed Cooling
ii)                  Raw Water Cooling

Both of these use water as the cooling medium, but it is the system which makes them different

The closed cooling system is similar to the cooling system of a car, only that the car engine uses air to cool, while the boat engine uses the water around the boat.

The closed cooling system has tubes which come into contact with the water, so the water can “cool” the coolant running through the tubes.

This system is also called the heat exchanger system. The tubes run around the engine, picking up the heat, and then into the heat exchanger, which is in contact with the water,and after the heat is exchanged, the coolant goes back into the engine and cools it down.

The raw water cooling system simply runs raw water around the engine, without having a heat exchanger.

This system is not preferable, since it brings in dirt and other contaminants into the engine.Now that you know much about the inboard engines, let’s move on to the outboard engine.

Outboard Engine

outboard motor

Image courtesy of boat-ed

As the name suggests, the outboard engine is one where the entire engine is bolted on the EXTERIOR at the transom of the boat.

These engines come with the drive systems mentioned in inboard engines, with the main difference being that they are bolted on the outside of the boat.

They have the upper section, which houses the power-head, the middle section, which is bolted to the transom using 4 to 6 bolts and the lower section.

INBOARD V OUTBOARD ENGINES (AESTHETICS, PERFORMANCE & SAFETY)

The advantages of either of the two engines will generally boil down to how you want to use your boat.

You should know about the true difference in the performance of the two engines in order to decide which is best for your boat.When it comes to aesthetics, the inboard engine is preferable to the outboard.

This is because the inboard is hidden and this allows you to have a boat that is aesthetically pleasing. You can have a design that you want and make it appealing to see.

The outboard engine, on the other hand, can seem like an eyesore as it sticks out at the back of the boat.When it comes to performance, there seems to be very little difference between an inboard and outboard engine.

However, the inboard engine allows for a better ride and trim, creating a different wake. The inboard motor creates better tow and is easy to maneuver.

When it comes to safety, the inboard motor can be a bit challenging given that you have to be very conscious about the depth of the water.

It is very easy to damage the inboard engine system, by hitting unseen rocks. Inboard engines are not suited to shallow water.

Outboard engines can be lifted higher so you do not hit rocks and other obstacle at the bottom. The only way to damage an outboard engine is to run aground at very high speeds.

Inboard v Outboard Engines (Saltwater)

There is a big preference for outboard engines when it comes to saltwater applications. Saltwater boat owners tend to like gasoline driven engines, and this applies to outboard engines.

Most inboard engines run on diesel.Apart from the fuel types, the main issue when it comes to saltwater applications is the issue of corrosion and the ease of dealing with it.

Saltwater will corrode your engine, which is the truth, no matter what kind of engine you use.

However, when it comes to the outboard engine, it is much easier to simply clip off the cover and do some cleaning to minimize corrosion.Inboard engines are bolted to the inside of the boat and are difficult to clean and maintain, and are therefore more susceptible to corrosion

.When corrosion renders the engine unusable,an outboard engine is easy to unbolt and replace. It will not require you to even take the boat out of the water.

When it comes to inboard engines, you will have to remove the boat from the water, and go through a complicated engineering process in order to replace the engine.

Storage is another issue when it comes to saltwater applications. If you are not using the boat, you can easily unbolt an outboard engine and store it safely away from the corrosive saltwater. The inboard engine remains on the boat and is therefore exposed to corrosion.

If you do not want to remove the outboard engine, you can simply trim it out of the water to reduce corrosion.

Outboard vs. Inboard Engines (Fuel Economy)

In the past, inboard engines used to guzzle more fuel when compared to outboard engines. However, with technological advancements, this has come to be a thing of the past.

Today, there is very little difference between the fuel economy of inboard and outboard engines.

However, there are various factors that will affect just how efficient your engine will be when it comes to fuel consumption. The type of fuel you use will affect the fuel efficiency.

For optimal performance, you should use REC 90 fuel, but in some places, this is not available, forcing you to use ethanol blended fuel.

This is not good for modern boat engines and affects the fuel economy, no matter which engine you use.

Another aspect that will affect the fuel economy of your engine, whether inboard or outboard is the combination that you use.

If you have a very heavy boat, and then you use an outboard engine, then your fuel economy will be terrible.

It is preferable to use an inboard engine in such a case, which produces more power for every unit of fuel used.

As a general rule of thumb, given optimal boat/engine combinations, the inboard engine has been found to be more economical when it comes to fuel consumption.

Inboard v Outboard Engines (Maintenance)

When it comes to maintenance, as mentioned in the section about saltwater, it seems like the outboard engine has lower maintenance costs when compared to inboard engines.

Well, let’s delve deeper and find out.In terms of performing maintenance tasks,it is much easier to service an outboard engine than an inboard engine.

All you have to do is remove the cowling and the full engine is exposed and maintenance can easily be done.

When it comes to inboard engines, the process is much more complicated.The frequency of maintenance also differs;inboard engines are somewhat protected by the hull of the boat.

They are safely tucked away, and you do not have to perform frequent maintenance tasks.Outboard engines, on the other hand, are exposed to the environment and require more frequent maintenance tasks, thereby driving up maintenance costs.

The costs of engine parts also differs between these two engine types. It may be difficult for you to believe this,but inboard engine parts are cheaper than outboard engine parts on average.

The average costs of inboard engine parts ranges from $200 to $500, while that of a 4-stroke outboard engine ranges from$300 to $1,000.

When it comes to replacement, it will cost you more to replace an inboard engine as opposed to an outboard engine.

The costs here may not relate to the engine per se, but to the actual operation of removing and replacing the engine.

As mentioned earlier, you simply unbolt and outboard engine and replace it with another, as opposed to having technical engineers coming in to help you remove an inboard engine from within the hull and replace it with a new one.

Here's an example of how to service an outboard motor.

Inboard vs. Outboard Engines (Longevity)

Once again, there was a time when inboard engines lasted much longer than outboard engines. However, that is no longer the case.

This may be due to the reason that it is much easier to maintain an outboard engine than in inboard.

Today, outboard engines last for about 8,000 to 10,000 running hours, while inboard engines last about 6,000 running hours.

By happenstance, outboard engines are mainly used for recreational boats which are rarely used. Inboard engines are used by boats that travel long distances and are used more frequently, thereby affecting their longevity.

Suffice it to say that use and maintenance are complimentary when it comes to the longevity of a boat engine, whether inboard or outboard.

Without proper maintenance, any of these engines will be rendered obsolete within 6 to 7 years of use, but with proper maintenance, they can last almost double that time the more frequently you use an engine, the more you should perform maintenance so it can last longer.

In one of the boating forums, a user says that he used an engine without an impeller for about 7 years. When complications arose, he added and impeller to save the life of the engine.

It took close to 12 hours of labor; the power-head had to be removed to replace drive shaft seals which had been corroded, increasing the bill further.

In the long run, he spent about $6,000 more. Regular maintenance would not have come to such a cost.

With proper maintenance, the longevity of an engine can range anywhere between 15 to 30 years.

The moral of the story is that the longevity of an engine is directly related to the number of hours that you use it, and how many times you maintain it.

Inboard vs. Outboard Engines (Reliability)

inboard and outboard reliability

Image courtesy of boat-ed

When you consider the reliability of inboard engines versus outboard engines, once again, this becomes a thing of the past.

Competition among engine manufacturers dictates that they produce the most reliable engine that they can. However,when run under the same conditions, inboard engines can be said to be more reliable than outboard engines, especially when it comes to power output.

An inboard engine will go through very challenging environments, where an outboard engine will fail.

For example, if a boat with the same weight and carrying capacity was fitted with the two engines for comparison, and then taken through a storm, the inboard engine will be more reliable.

The outboard engine may stall or blow out,while the inboard engine chugs along comfortably.

Therefore, if you are running a boat that goes for long distances and moves through the challenges of the high seas, then using a inboard engine will give you better reliability than an outboard engine.

As a rule of thumb, you need to know the purposes of the boat and then decide on which engine will be more reliable.

If you just want a recreational boat to run along the harbor over the weekends,then go for an outboard engine.

If you are a commercial fisherman who spends a lot of time out in the water under tough conditions, then go for an inboard engine.

Are Inboard Motors Bad?

In order to properly address this question,let us look at some of the basic and important aspects of inboard motors.

a)     Performance

Inboard motors tend to perform better than outboard motors when it comes to propulsion power per unit of fuel used.

This is one of the main reasons why large boats are fitted with inboard motors. An inboard motor will propel a boat through tough water conditions where an outboard motor will not.

On the other hand, since the weight of the engine, especially when located in the middle section, makes the boat sit deeper in the water.

This produces a higher drag and affects the cruising and top speed.

b)     Maintenance

Maintaining an inboard motor is difficult and costly. This is mainly due to the positioning of the engine. It is costlier to maintain an inboard motor, although this cost is alleviated by the cheaper costs per part.

c)      Aesthetics

On this aspect, inboard motors are the best, hands down. They are fitted in the boat and do not affect the outward appearance of the boat.

d)    Longevity

When you look at the running hours of an inboard motor vs. outboard motor, all other things kept constant, the inboard motor will outlast an outboard motor.

e)     Safety

An inboard motor requires much more attention from the pilot when it comes to safety. The fact that it cannot be trimmed out of water means that the pilot has to be very careful when sailing through shallow waters, or else he risks running the propellers into rocks.

An outboard motor can be trimmed and is therefore much safer in shallow waters.

f)      Storage

In this case, the inboard motor is at a disadvantage.The motor is perennially bolted to the inside of the boat and cannot be removed for storage when the boat is not in use.

This means that during winter, it will be exposed to ice. When in saltwater, the motor will be exposed to the corrosion of the salt.

g)     Cockpit space

In most cases, the engine will be situated in the middle section of the boat. The engine box will therefore take up a lot of cockpit space.

So weighing up the pros and cons of both inboard and outboard motors, one would have to say the inboard motor is better than an outboard one (however, this is based on particular circumstances.

ADVANTAGES OF OUTBOARD MOTORS

As we have seen through this article,outboard motors have certain inherent advantages and these are:

a)    Maintenance

It is much easier to maintain an outboard motor when compared to an inboard motor. You only have to remove the cowling to expose the motor and you can easily maintain it.

The inboard motor requires a much more complicated process.

b)     Safety

Thanks to the ability of trimming the motor, the outboard motor is safer to use in shallow waters when compared to outboard motors.

The only thing required is to know how much trim is required and you can trim the motor. This also allows outboard motor boats to sail through shallower waters than inboard motor boats.

If you are operating on a river, then this is the motor that you should have.

c)     Speed

Perhaps it is because outboard motors are used on smaller boats, but they tend to propel the boar faster than inboard motors.

This is further supported by the fact that you can trim the motor so that it lifts the hull from the water, reducing the drag and making the boat speed along at a faster clip.

d)    Storage

During winter, or when operating in saltwater, storage is crucial to the life of the motor. An outboard motor can be trimmed out of the water, or removed entirely and stored safely away from saltwater or winter ice.

Inboard motors have to remain on the boat, exposing the engine parts to the saltwater and winter ice, and this makes them corrode much faster.

e)    Cockpit space

The engine is located at the transom,thereby leaving a lot of space for the cockpit. The cockpit can therefore be used for various reasons, such as storing fishing poles, etc.

INBOARD AND OUTBOARD MOTORS (HIGHLIGHTS)

Here are some of the highlights of these two engine types:

Inboard Engines
·        Inboard engines have a higher fuel efficiency
·        Properly maintained, the engine can have an average life of more than 6,000 hours
·        When drifting, the engine weight, centering and location makes the boat more stable, even when drifting
·        For people who fish, the boat can carry more weight in the lower transom areas
·        Inboard engines have a higher initial cost
·        The weight of the engine makes the boat sit lower in the water, thereby producing more spray and also slowing it down to a certain extent
.·        The boat has a low cruising and top speed
·        The engine box will take up more space in the cockpit
·        Complex maintenance repair and storage
·        The engine requires a trolling valve

Outboard Engines

·        Outboard motors have a lower initial cost
·        The boats have a higher cruising and top speed
·        The boats have a larger cockpit suitable for variable uses
·        When properly maintained the engine has a life of more than 6,000 hours
·        The engine is easy to maintain,repair and store
·        The boat has a great Zip wake-trim, which lifts the boat from the water improving performance and comfort
·        Having two outboard engines on the boat reduces redundancy Low Points
·        Outboard motors have a lower fuel efficiency
·        They do not need a lot of servicing like their inboard counterparts
·        You cannot store a lot of fish around the transom

After getting to know some of the basics of inboard and outboard motors, it is high time that you got to learn more about the motor boats that these engines drive. Here are some examples:

EXAMPLES OF OUTBOARD MOTORBOATS

1)      Sea Pro 239

outboard motor example

Image courtesy of Popular Mechanics

Suzuki is popularly known to produce outboard engines of note. The DF350A is one of their flagship outdoor engines,ranging high in the horsepower game.

It has a huge 4.4 liter naturally aspirated V6, having a pair of counter-rotating propellers to increase the grip on the water and reduce negative torque effects.

For all single-engine boats,the negation of negative torque is very relevant and the DF350A excels in this aspect.

The Sea Pro 239 uses the DFA350A, which push the boat to speeds of up to 54.2 mph, with 3.35 miles per gallon consumption when at cruise speed in the high 20s.

An Aluminum Gaudet 38 was propelled by Quad 350s to speeds of 65.8 mph. In keeping with the Suzuki modusoperandi, the DF350A has a lot of power per buck used.

The MSRP goes for$31,565, while the DF350A has been offered at $24,000

2)      Scout

are outboard motors bad ?

Image courtesy of Popular Mechanics

It has now become the norm for outboard motorboat designers to stretch the center console quite a bit. Some go as far as 50 feet, with battle-wagon express boats being converted from inboard engines to outboards.

In order to cope with this growing trend, Yamaha went and designed an engine that can propel a boat of 50 feet or more.

This is the 425 horsepower XTO Offshore. This is a 5.6 liter V8, having direct fuel injection for extra power whenever you need it.

The XTO is a giant, with an integrated power steering, and weighs at about 999 pounds – a single pound short of 1,000 pounds.

However, some builders, as seen in the Scout shown above, have gone ahead and hang up to 5 of these big fellas on the stern.

Yamaha says that quad XTO configuration can propel a 41-foot

Regulator center console to a max speed of 63.7 mph.

One the other hand, you can opt for a single XTO having 200 horsepower twins; a single XTO will propel a 25-foot Sportsman boat at speeds reaching 55 mph and consume fuel at a rate of 2.83 miles per gallon at a steady 29 mph cruise.

3)      Dinghy and Small Sailboats

outboard engines

Image courtesy of Popular Mechanics

Torqueedo is a company that specializes in making outboard engines for dinghy’s and small sailboats, even if it has a few large engines for big boats.

These small engines are targeted at the rich billionaires who have a Yacht or two or those who are in the import-export business and might need a small dinghy or sailboat to carry their wares.

While the big Deep Blue engines together with a battery pack developed by BMW are pretty pricey, coming in at a cost of $50,000, the Travel 1103C costs $2,699 and can propel a boat with a maximum weight of 3,300 pounds.

The 1103 comes with a 915 WH lithium battery and can go for a full 6 hours when running at half throttle. This means that you can travel 18 miles on water, using an average weight dinghy.

Although the Torqueedo is ideally targeted at dinghies and small sailboats, it can also be ingenuously used as a kicker for a small powerboat or a trolling motor.

It is quite silent, emitting only 33Db of noise. It weighs less than 40 pounds so you can easily carry it along. If you want to go for long distances, pack a solar panel and use it to charge the battery as you go along.

EXAMPLES OF INBOARD MOTOR BOATS

1)      The Sea Ray Range

inboard boat examples

Image courtesy of Boats.com

Does anyone doubt the Sea Ray? Actually,the brand is one of the most sought-after, according to the Ranker List.

It outranks other huge manufacturers, such as CSI, Product Quality, J.D. Power& Associates, NMMA and many more.

Another indicator of the popularity of this inboard motor boat is that the dealers rank among the top 100 dealers in the world.

They produce inboard motor boats ranging from the 19-foot Bowriderall the way to huge 65-foot Yachts.

2)     Chaparral

chaparral outboard motor

Image courtesy of Boats.com

Chaparral is another brand that makes boats with inboard motors. They have 38 different models ranging from 11’ to 42’.

It has a long and reputable history, earning the name of the “unsinkable Legend”.

Apart from the craftsmanship of the boats, the company insists on having the best engines running in the belly of the boat.

Chaparral has collected 15 consecutive Consumer Satisfaction Index Awards, and the NMMA Innovation Award.

As far as inboard motor boats go, this is one of the best that you will find on the market. It has a high resale value, with some 20 year-old models selling at above $60,000.

3)     MasterCare

Image courtesy of Boats.com

It’s now time to think about inboard motor water-sports boats, with very few brands topping the princely rank of  MasterCraft.

This marvel occupied the 6th position on Ranker’s. It has won several engineering and innovation awards, taking the helm in 5 of the awards for the last 6 years.

Their manufacturing plant in Vonore, TN has even won awards for the use of advanced technology in manufacturing.

MasterCraft also gives customers a 5-year MasterCare warranty, covering the boat from stem to stern. The warranty is fully transferable to another model from the same company.

CONCLUSION

The inboard vs. outboard argument is one that has been going on for years.

Every model has its own fans, for whatever reasons.Take the example, where a couple removed their inboard engine and converted the boat to have a transom to fit in some outboard motors, just because they love the roar of the engines.

Many stories abound, but common sense dictates that one should carefully weigh a lot of factors before deciding on using an inboard or outboard engine.

When you truly think of having a custom boat, you should be careful about this combination.

On the other hand, you may take the safer route by deciding on the type of engine that you want, and then letting the manufacturer give you the best combination.

It all depends on your preferences.After having gone through the article, you are now properly voiced with the important aspects of the inboard vs. outboard discussion


Paul L

I enjoy blogging, business & sailing. From Ireland, I've loved sailing from a young age and love to hit the waters whenever I have time. You can check out more info in the about us section. Hopefully you're enjoying the site and if you have any questions, you can reach out (just subject the email with my name) so it'll get sent to me and I'll happily get back to you. Feel free to share photos and stories of your sailing experiences with us too

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