Why are props at the back of a ship but at the front on a plane?

[JasonDS]

I'm interested in humorous and technical reasons. I'm no engineer (as you can tell) but don't hold back on the technical reasons, I can always look up big words.
Has anyone ever build a ship our boat with the main drive at the bow (not counting bow thrusters) ?

[newhaul]

Pusher aircraft are still around
https://en.m.wikipedia.org/wiki/List..._configuration

And they are more efficient than traditional prop configurations
https://aviation.stackexchange.com/q...e-still-around

Hope this helps your curiosity. (In reference to aircraft) also crosses quite well to vessels )

[JasonDS]

Ship OR boat

[atoll]

try running aground in reverse in your dinghy,you will find the outboard is unable to kick up before the propeller gets chewed up..........

however i would surmise, since the propeller is a relatively new invention for propelling sailing vessels i would guess it was easier to drill a hole in the stern post and cut out the rudder than in the bow.......it also would help avoid damage to the propeller when launching or beaching in traditional boats with a semi or full keel.

not to mention the benefits of prop wash over the rudder for steerage before the boat has any way on.

a boat with a propeller in front,and rudder on the stern would be unable to steer untill the rudder had sufficient water passing it,assuming the propeller in the front was fixed.

[Steadman Uhlich]

I like ATOLL's answers.

______________

You all might find this thread intersecting....or interesting.
It describes and shows a new ship (and others) that use "AZIPODS" and in one case the use is for the boat to "go in reverse" a long, long way, with what appears to be the stern of the boat actually going first. See the link for more.

http://www.cruisersforum.com/forums/...ml#post2464367

[atoll]

Originally Posted by Steady Hand

I like ATOLL's answers.

______________

You all might find this thread intersecting....or interesting.
It describes and shows a new ship (and others) that use "AZIPODS" and in one case the use is for the boat to "go in reverse" a long, long way, with what appears to be the stern of the boat actually going first. See the link for more.

http://www.cruisersforum.com/forums/...ml#post2464367

modern tug's, use this system where the 360 degree steerable propeller is mounted mid ships, but not much use on a sailing vessel!

[Suijin]

I expect there is an efficiency issue as well, where a prop forcing disorganized water flow over the hull surface leads to poorer efficiency...or even pushing water against the hull which reduces the efficiency of the prop itself.

And unless the prop shaft was straight and level, it would be pulling the bow of the boat down...and also lead to an exposed prop when making headway into larger seas.

[Panope]

AIRCRAFT:

-Propeller in front has better ground clearance with shorter/lighter landing gear legs.
-Propeller in front is damaged less from objects (rocks) being kicked up by wheels.
-Propeller in Rear is damaged by ANY object that departs the aircraft in flight (nuts, bolts, gas caps, etc,) (lives have been lost due to this).
-Engine in front of passenger cabin is safer in crash.
-Engine in front of passenger cabin is closer to aircraft C.G.
-Engine in front of passenger cabin is closer to the fattest part of the aircraft. (fuselages are pointy in the back. Drive lines that extend the prop rearward are heavy, complicated and problematic).

There is a slight, theoretical efficiency advantage possible with a pusher propeller. Yes, the accelerated prop-wash does not have to be blown past the fuselage. However, the air that a pusher propeller receives is "dirty" having already passed by the fuselage, thus negating most of the efficiency gain.

BOAT:

-Prop in rear is protected from floating object and grounding damage by the keel and hull.

Steve

[sailstoo]

Where's Bob Perry when you need him?

[bobnlesley]

Originally Posted by Panope

AIRCRAFT:
-Engine in front of passenger cabin is safer in crash.
Steve

How/why? Surely it would sting a bit whether you slammed into the back of it, or it slammed into the back of you?

[Flyingriki]

Mine's in the back...!

[Suijin]

Originally Posted by sailstoo

Where's Bob Perry when you need him?

Over at Sailing Anarchy after he got kicked off here lol. He's salty

[model 10]

Originally Posted by bobnlesley

How/why? Surely it would sting a bit whether you slammed into the back of it, or it slammed into the back of you?

Airplanes are not designed to crash. The Long EZ in the post above is about as dangerous as it get's, but who cares?

[newhaul]

Originally Posted by Flyingriki

Mine's in the back...!

Good looking lil canard. Where is she ported? (Would love.some stick time )

[Hydra]

The main reason for having the propeller at the stern of a ship is efficiency.
1 The friction of water on the hull creates a "boundary layer" where the flow is slower. This slower flow feeding the propeller gives more thrust.
2 The propeller provides thrust by accelerating the flow. If the hull were in this faster flow, the friction would be increased, resulting in a loss of useable thrust.

The second reason is seakeeping: in a seaway, it is not uncommon that the whole stem comes out of the water. If the propeller were there, big trouble would result.

Steering effectiveness wasn't a primary reason: in the past, many ships had 2 propellers but only one rudder.

Alain