4 Common Types Of Propulsion For Boats

Boats seem simple, they float and move you’re across the water, right? Well, it can be just a little more complicated than just that.  Let’s take a look at those 4 common types Of propulsion for boats. I’ll review the Pros and Cons for each type to give you a good idea about each.

Outboard Motor

Outboard motors are likely the ones you think of when you think of a small powerboat.  They are by far the most common type when it comes to freshwater small boats from fishing boats to pontoon boats.

Outboard motor placement is typically mounted to the rear transom, or rear ‘wall’ of the boat.  The motor is completely contained, save for the gas tank which is external to the motor. This type of propulsion for boats is very common.

When operating, the steering of boats that utilize outboard motors is done by moving the entire motor itself.  There are many different types, sizes and so on of outboard motors, but let’s take a look at a few of the key good and bad points for each type.

PRO – Outboard

• Easy to get into a shop if repairs are needed.  As these units are mounted externally, you don’t need to bring the entire boat to a repair shop.  Nor do you have to call a mechanic to come out to your boat at the marina. That’s a bill you don’t want to have to pay, believe me.
• Relatively easy to maintain.  Due to the ‘open concept’ motor placement, it is one of the easiest motors to do maintenance in terms of accessibility.

CON – Outboard

• Noisy.  These motors are not enclosed within any kind of soundproofed enclosure, so they are typically quite loud.
• Inefficient.  Due to an open propeller blade design, these types of motors are not the most efficient out on the water.
• Dangerous.  Again, due to the open propeller blade design, these types of motors can be dangerous to swimmers and marine life alike.  Just watch a documentary about whales or dolphins. You can usually spot the one that rubbed up against a boat and discovered the propeller. Shivers just ran down my spine at the thought.
• Pollutes.  Take one out for a spin and you’ll notice the trail of oil these motors leave behind.  If it’s water-cooled, it leaves the oil in the water. I’m not so happy about this one, to be completely honest.

Inboard Motor

The Inboard Motor is usually mounted inside the hull, in the front or middle of the boat.  The engine turns a drive shaft, which turns the propeller. These types of propulsion for boats are usually visible, as they are often encased within the hull, out of common sight.

Boats that use inboard motors do not turn the motor in order to steer.  The motor, driveshaft, and propeller are typically fixed in position. These boats utilize one or more rudders for steering.  Let’s take a look at the pros and cons of inboard motors.

PRO – Inboard Motor

• Quiet.  These motors are usually quiet when compared to outboard motors.  This is because they are usually mounted within the hull. The engine compartments are typically vented, but also they are often sound-proofed to some degree.  The concept of these propulsion setup types is to conceal the motor and drive components. The idea is for the mechanics to be out of sight and mind. This is why many luxury watercraft use this type of setup.

CON – Inboard Motor

• Difficult Access.  These motors are mounted in a concealing manner.  Therefore, they can be hard to access to do regular maintenance.  They can be even more difficult to work with if you need to do any kind of serious repair.  
• Lack of Efficiency.  This type of motor setup loses power as the motor transfers its force through the drive shaft.  It’s not much loss, but its a loss none the less.
• Steering Power.  Many of these types of setups utilize a rudder or multiple rudders.  This can decrease the turning ability as the rudder is, to some minor effect, working against the motor and propeller as these are fixed and the force vector is always directly ahead.  This means that turning under power is guaranteed to be an inefficient use of energy.

Sterndrive 

Sterndrives are also known as inboard/outboard or I/O drives for short.  A sterndrive setup is very similar to the inboard motor setup in the sense that again the motor is concealed as well as fixed in position.  The difference is that, as the name implies, the motor is mounted at the rear of the boat, but in front of the transom. This is where it is similar to an outboard motor, by being at the rear of the boat.  The difference is however again pronounced by the fact that the sterndrive motor is fixed in position and again does not move to steer as the outboard motor does. However, the propeller portion of the drive does move to act as a rudder, just like with an outboard motor.  So, the sterndrive is sort of a hybrid.

PRO – Sterndrive

• More Power.  The sterndrive typically delivers better performance than both inboard and outboard motor setups.  This is because the motor has more of a direct, and short shaft to turn compared to inboard which is a long driveshaft, and outboard which has to work through two angles to deliver power out the base of the motor assembly at the propeller.  That’s because the propeller of the outboard motor is not ‘in-line’ with the turning shaft of the motor.
• Turning Ability.  Like the outboard, this motor has a decent ability to turn a boat because the propeller itself turns.  This forces the water in the direction the propeller is facing and thus does not require a rudder as an added steering component.

CON – Sterndrive

• Difficult Access.  Like the inboard motor, these boats can be difficult to access the motor to do maintenance.  A lot of the newer models of sterndrive boats solve many of the access issues, but these boat motors will never be as accessible as an outboard motor.
• Dangerous.  Again, we have a powered open concept propeller.  This could harm swimmers or marine life.
• No Saltwater.  These types of drives are not recommended (typically) to be used in saltwater.
• Higher Cost To Maintain.  Because these motor setups use a shaft to go to a separate propeller assembly, there are greater chances of mechanical malfunction.  Also, due to the concealed nature of the engine, the cost of maintenance is usually higher for sterndrive boats as well.

Jet Drive

Ok, so the jet boat doesn’t actually use a jet engine.  Too bad, that’d be cool, right? They do use a motor and propeller (impeller) which is mounted inside the boat, in a special chamber.  The idea here is that there is an inlet for water and the water passes through a chamber where the impeller is mounted. The impeller speeds the water up, blasting it out the back.  This causes a forward pushing force on the boat.  

This type of propulsion for boats is typically used on the widely known personal watercraft ‘jet-skis’.  There are some pretty decent boats that also use this type of motor setup. These boats are usually used for water sports where speed and quick maneuverability are strongly desired.

PRO – Jet Drive

• Safety.  Being that the impeller is contained within a chamber in the propulsion system, a swimmer or marine life is not likely to get an injury from the propeller.  Not like with an outboard or sterndrive where a swimmer who gets too close to a moving propeller could be seriously injured or killed even.
• Powerful.  This type of propulsion for boats typically delivers a lot of kick.  That means that these boats and watercraft can really rip across the water.
• Low Maintenance.  Although the motor is concealed, these types of drive setup usually require much less maintenance.  This is due to a lack of extra parts. No need to raise or lower a propeller assembly with these types of boats and watercraft.  So, the maintenance required is usually considerably less than the other main types of boat motor types.

CON – Jet Drive

• Expensive.  This is probably the most expensive form of boat you can buy for the size of the boat.  They are not usually cheaper than outboard or inboard. Sometimes, prices are similar to sterndrive boats, but from what I’ve seen Jet Boats are the most expensive.
• Noisy.  If you’ve ever been out on the water relaxing when a jetski has torn past, then you’ll know they sound like the loud go-carts of the sea.  But when you’re ripping around on a jet ski, it’s too much fun to care about the noise, right?

And those are the 4 common types of propulsion for boats.  Each having a different use and different pros and cons to each.  Depending on what kind of boat you have, you’ll likely be running one of these propulsion types. 

If you’re doing research on what type of boat to get, check out my article on different boat hull types.  I go through all the basic hull types and differences with benefits to each type. Don’t forget to leave me a comment about your boating experiences.

Bibliography

• wikipedia.org
• hagadonemarine.com
• boatus.com
  

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