Why wouldn't mounting a fan on a sailboat work ?

Question

Hi all...

It's like this :

"mounting a fan on a sailboat and then pointing the fan at the sail to move the boat"...

>>>Why wouldn't it work ??

I probably would get bashed by asking this stupid question.

Cheers...

Answer 1

Listen bloke, you're talking about a huge, huge fan here. Think about it: does a housefan blow you over while you're sitting there? Well you're asking a "ship-fan" to put forth a million times that pressure in order to move a boat through water. And then the size of the generator you would need to power such a huge, huge fan...and then the weight of all the gas needed to power the generator. You'd be going under before you even started, or tilted and flipped by the sheer weight of the fan on one side of such a boat.

Answer 2

It would if you pointed it the other way, like the fans on air boats, dig. with a big engine If you place the bigger fan the other way it would move the boat backards, off seting the wind going in to the sail. That like using a generator to drive a electric motor driving the generator. Yes it been tryed, it does not work.

Answer 3

Sorry friend, but there is just not enough wind from a fan to move the boat. I could list several other reasons but they'd all have to do with physics and I'm just too tired to bother a good bloke like you with that.

Answer 4

This is a fun question.  Physics textbooks for years said that this doesn't work.  Some of them STILL say this.

Here's a website that says it doesn't work - http://www.weathernotebook.org/transcrip...

But it DOES work!  It's *not* an 'equal and opposite reaction.'

Yes, the force of the fan pushing backwards cancels out the force of the air hitting the sail.  BUT there's another force that comes into play - the redirected airflow in the sail.  What you would have is a simple thrust vectoring device.  The air, after getting caught in the sail, has to *go* somewhere.  The curved surface of the sail directs the airflow again towards the back of the boat and gives forward acceleration.

Next time you see a big jet airliner landing, watch how they slow down after they touch down.  They have flap/nozzle things that fold down behind the jet exhaust.  The exhaust, which normally pushes the jet forward, is now pushing against the flap, and *the jet slows down and stops!*  It's the same thing, the jet exhaust is the fan and the flap is the sail.  The jet has redirected the thrust and gained a net force which causes an acceleration (in this case a deceleration.)  A fan on a sailboat does the exact same thing.

The most fun thing about this question is the fact that we HAD jets that did this long before the physics community realized it actually works.  It's a great example of letting our theories about how the world SHOULD work get in the way of our observations of what actually DOES work.

And yes, this can be proven in a laboratory.  You need a low friction physics cart with a sail, and a powerful fan like something off a model airplane.

It's not a stupid question as you can see, everyone who posted so far got it wrong.  Sometimes it's the seemingly simple questions that give the most unexpected answers.

Answer 5

Lets forget for a few seconds that a sail boat works by having both wind against the sail and water press against the hull of the boat.   Kind of like when you squeeze a seed between your fingers.

Oposites and equal forces cancel each other out.

Fan blows in one direction and generates force while the air from the fan pushes against the sail and cansels out the force of the fan.

Answer 6

Hi,

The sailboat moves due to air/wind pushing the sail in the direction of the movement of the boat. Note that air/wind and sail are not mounted on same body ie the sail is mounted on the boat and air/wind is not physically interlinked with the boat by any means. Actually the air pushes the sail in the forward direction and in the result the sail moves forward and as sail and boat are attached to each other so does the boat.

Now consider a fan also mounted to the boat. The fan pushes the sail in the forward direction which tends to move the ship in forward direction. But due to Newton's third law of motion (action and reaction are equal in magnitude/quantity but opposite in direction) , the sail also pushes the fan backwards with equal magnitude. As fan is mounted on the boat, thus it tends to move the ship backwards. Therefore the resultant is zero and the ship does not move.

Note: if there is no sail and the fan is mounted in such a way that it throws air in the direction opposite to the desired direction of movement of the boat, the boat will move. This is again due to Newton's third law of motion.

Hope to answer you well. Keep smiling. Bye.

Answer 7

This is a trick question. Reading the scenario I pictured a large fan mounted to the boat fruitlessly blowing on a billowing sail producing no movement. But the fan boats of the everglades fly along at high speed using nothing but a mounted fan for propulsion. All you have to do is point the fan away from the sail and movement will be produced, and maximized when the air was blown directly away from the stern