Because while boat props just push the boat through the water, airplane propellers not only push the plane forward but also create lift by forcing air over the wings. That having been said, there *are* rear prop planes that are just less common.

Boats are also more likely to come into contact with miscellaneous materials or creatures in the water than planes are in the air and putting their props in the back let the hull clear a lot of that out of the way. Finally, a boat’s prop being near its rudder allows its steering to be more effective for similar reasons to why locating planes’ props on the front of their wings generates slightly more effective lift.

Editing to add the ELI5 major factor in the location of props and the engines that drive them and most of the comments are pointing out: **Balance.** Hydrodynamics, especially on the surface are very different from aerodynamics. A boat benefits from pitching back a certain amount in the water and so the weight and thrust are often best located toward the back. An airplane needs to delicately maintain very close to perfect balance in the air and so their fuel and engines are most efficiently located the wings. Thanks everybody!

some planes do have the props behind, it really doesnt matter to them. the front is better since it pushes air over the wings even if the plane isnt moving, so the control surfaces still work (ish)

Boats though, have the engine in the back since, when they go fast, the front end rises out of the water. Its basically pushed out by the fast “moving” water. If the engine was on the front it would stop working, but since its on the rear it keeps working.

Boat engines are water cooled and thus can be placed anywhere convenient. The stern is generally better than the bow because that way you’re not sitting in the exhaust and noise. It’s not uncommon to see trolling motors mounted on the front, as they don’t have exhaust and locating them there makes them easy to operate by hand.

In contrast, aero engines are (today at least) universally air cooled and/or turbines, both of which desire large volumes of clean airflow. The best place to get that is on the front of the plane or the front of the wings.

It is certainly possible to make pusher prop planes, as the B-36 or Long EZ demonstrates. But generally this is more difficult as it gets more turbulent airflow and you need to design to that. Using a puller prop also leads to some issues as the now high-speed rotating air interacts with the rest of the plane, but after a century of trying we know how to deal with those issues.

There are also design constraints that apply to planes that don’t with boats. For instance, the BD-5 had a pusher that was located above the bulk of the fuselage. If you increased the throttle it would push the nose down.

If you are coming into land and you notice you are a little low, you want to add power to flatten out the path. So you increase throttle and… the nose is jammed into the dirt. The first three completed all killed their pilots on their first landings.

In contrast, in a Cessna the engine is slightly above the fuselage midline, deliberately, and on the front. So increasing the throttle pulls the nose up – which is precisely what you want.

You can design this out too, say by putting a pusher prop lower than the fuselage, but again, it’s just more work and things to consider.

A rear prop on a plane is subject to FOD. Anything kicked up by the wheels on a runway gets sucked right into the prop. Whoopsie.

Depends on the design. Most propeller driven aircraft are configured in a tractor configuration (prop pulls the surface it is mounted to). Some are configured in a pusher configuration (common for single engine amphibious aircraft) like the the X/YB-35, and then there are they hybrids which utilize push-pull configurations such as the Cessna 336/337 Skymaster, the B-36 Peacemaker (which uses inboard radials in a pusher config and outboard turbojets in a tractor config though all engines are wing mounted), etc. As for boats, most are configured in a pusher configuration however there are exceptions with some push-pull used on bay ferries and then the weird Voith Schneider Prop design that some tugs and fireboats use…not even touching on azimuth/pod thrusters and the weird places you are beginning to see those.

Lots of good reasons here but an another is that planes have to point the nose up a bit when taking off and landing. With the nose up it means the tail is down and with the prop in the back there is more danger of hitting in on the ground or debris kicked up from the tires. This can be overcome but it’s just easier and more practical to put it up front.

Plane propeller locations can be either in [pusher (back of plane)](https://en.wikipedia.org/wiki/Pusher_configuration), [tractor (front of plane)](https://en.wikipedia.org/wiki/Tractor_configuration), or [both](https://en.wikipedia.org/wiki/Push-pull_configuration). There’s engineering tradeoffs for all of those decisions, but of note, the first airplane was a pusher airplane (wright flyer) as are [Reaper drones](https://en.wikipedia.org/wiki/General_Atomics_MQ-9_Reaper). In general, in an airplane, having a tractor configuration in the front of the plane can be more efficient, in that the air is undisturbed by the aerodynamics of the plane – at the expense of having a heavy object in the front of the plane (and for warplanes, being in the way of cockpit mounted guns).

Boats as others say, benefit from the change in weight distribution for a smaller boat with a rear mounted outboard motor. But you do see bow mounted trolling motors, and very large ships often have many [thrusters](https://en.wikipedia.org/wiki/Azimuth_thruster).

It really comes down to engineering benefits of engine placement, how you get power from the engine to the propeller, and the turbulence/efficiency of the propeller placement. The purpose and use of a boat or an airplane also factors in. For example, if you need guns, but want a propeller, that will influence positioning. Propellers on wings for planes create drag, and there’s less drag with a center mounted engine.

For most simple purposes, the more efficient place to put a single propeller+motor in a plane is the front, and the most efficient place to put a propeller+motor in a boat is in the back.

There are aerodynamic and design considerations that favor pusher style planes with the propeller at the rear.

However this usually required putting the engine in the back and the pilot in front of it, which in a crash landing could cause the pilot to be crushed by the engine.

Keep in mind back when prop planes were still the peak of plane design, wind tunnels were not nearly as common or plentiful so planes had to be developed based on inherited technical know how and painful repeated testing. This lead to a strong bias towards existing designs and concepts. Still planes of this type were developed.

Such as the J7W, which is one of the fastest warplanes to ever make use of propeller based propulsion.

https://en.wikipedia.org/wiki/Kyushu_J7W_Shinden

Not all planes, piaggio p.180 Avanti has rear facing props, and a fair few planes had engines at the back in the 70s/80s but central like all modern planes, the importance of engine placement on planes is particularly due to weight distribution also, a boat is shaped to float so anything at the front wouldn’t work either

Aircraft propellers usually last longer if they are ahead of the landing gear, rather than behind them.

When an airplane takes off or lands, sometimes the landing gear kicks up bits of debris from the runway.

Preferences in performance characteristics and trade offs, as well as inertia of design conventions.

You can have front, rear, and even mid mounted prop engines for either boats or planes.

Planes operate by lift, the location of the source of proportion affects the flight characteristics, but the type of propulsion whether props, or jets, or even rockets don’t matter. You can find videos of the Air Force test launching a C130 with rocket boosters for a very short runway. While the engines if the plane are front. mounted on the wings, the rockets are mid mounted just behind the wings iirc.

And this is also a useful distinction. For larger cargo and passenger planes, the source of propulsion is usually mounted on the wings, with is close to the center of mass, while the directional controls are usually focus on the tail section. This is to improve stability in flight, but makes the plane less maneuveable. Fighter jets have their jets along the full body, but the thrust comes out the rear of the plane. It gives them a lot more instability, but that instability provides manueverability. There is a trainer plane, called the Fantrainer that has a mid body propeller which was designed to provide similar manueverability to a fighter jet, when jets were new.

For boats you can likewise mount your propulsion anywhere along the body. Boats float, which is they displace more water mass than the mass of the boat. Where and what type of propulsion has to be balanced with the the fact that boats navigate mostly in 2 dimensions, and have to contend with the much greater friction of the hull. Common rowboat the propulsion is mid mounted, Sailbots their propulsion is above the water. Some fishing motors may have a Lower power trolling motor mounted to the front of the boat. Proper design of a boat takes into the forces from propulsion and accounts for the different rotational forces from the fiction, and bouyancy and propulsion forces to keep movement along the plane of the surface. When those aren’t balanced, you can have a boat drive itself underwater, roll over, or even fly into the air (motor racing boats have this problem).

For most boats the tiller is placed in the rear of the boat in a dragging orientation: the “blade” of the tiller extends backward from the direction of travel from the fulcum point it’s source of rotation. This allows a tiller with no other forces to be corrected back to a center position as it balances the flow of water across its two sides. If the blade was leading it’s fulcrum point, it would be unstable and as it stats turning more force would keep it to one side or the other. This applies for planes and boats. You can mount a tiller with a rearblade at the front of the boat. And it works fine. However it’s more likely to get damaged, and you won’t be able to beach the boat without damaging it.

On a plane, the prop can go on the front or the back.

On a boat, you’re rather have the back of the boat in the water than the front.

🙂

Because planes need to be PULLED through the air and boats need to be PUSHED through the water.

Can I just say, to me, this is a great case example of a question for ELI5. And that is a compliment.

Easy answer is that the engines are mounted in the front so that the center of balance of the aircraft is also forward. Meaning the nose of the aircraft is heavier than the tail. This configuration keeps the aircraft pointed forward. Think of it like a throwing dart. How well would a throwing dart fly if most of the weight was at the back? It wouldn’t do well. It would flip around and fly backwards.

With the (heavy) engines near the front, the aircraft tends to point in the direction of flight. As others have said, it also contributes to lift in many aircraft. The weight being forward also makes the aircraft tend to nose down if you let go of the controls, which increases velocity and lift, helping it to fly again if for some reason it stalls. This also helps the control surfaces actually work so that the pilot can make corrections. When things start going bad with an aircraft, a good pilot typically pushes the nose down to give him more control.