Powerful fans on boat, blow to own sails, would this move the boat?

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A sail boat got stuck because there is absolutely no wind. The boat happens to have some powerful fans. Which are then bolted on deck and blow to the sails.

Would that make the boat move?
  1. When the artificial wind direction is horizontal (0 degree)
  2. When the wind direction is 45 degrees.
Would appreciate some explanation because I am not sure about the answers. I think Q1 will not move the boat. Q2 will move it, but in negligible proportions.
 
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  • #2
Trikenstein said:
Would that make the boat move?
Yes, but not in the way the wind does.
Air drawn into the fan, will mostly pull the boat that way.
The sail will deflect the blown air, and so will push the boat away somewhat, but also along.

To go faster, take the sail down.
 
  • #3
There are several demonstrations of this experiment with variations, e.g., here.
 
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  • #4
Hill said:
There are several demonstrations of this experiment with variations, e.g., here.
Thanks for the video suggestion. Now I see the importance of the curve shape of the sail. There has to be something pushing the air backward.

In my thought experiment, I simplified the problem as a person standing on the deck, pushing on the mat with a stick. Obviously the system is in equilibrium within the boat itself and would not move the boat. Kind of demonstrated in the video when the sail is perfectly flat.
 
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  • #5
Trikenstein said:
Kind of demonstrated in the video when the sail is perfectly flat.
With a flat sail you would want to blow at it from the side, at an acute angle of attack, while it is oriented to divert the air backwards. But as already said, you would be much better off using just the fan, blowing air backwards.
 
  • #7
Trikenstein said:
A sail boat got stuck because there is absolutely no wind. The boat happens to have some powerful fans. Which are then bolted on deck and blow to the sails.
Airboat go fast:
1704158978483.jpeg


Airboat with parachute pulled behind it go slow/zero... :wink:
 
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FAQ: Powerful fans on boat, blow to own sails, would this move the boat?

Can a boat move forward if it uses powerful fans to blow air into its own sails?

No, a boat cannot move forward if it uses powerful fans to blow air into its own sails. This is because the force generated by the fans pushing air into the sails would be counteracted by the equal and opposite force of the fans pushing against the boat. According to Newton's third law of motion, these forces would cancel each other out, resulting in no net movement.

Why doesn't the boat move if the fans blow air into the sails?

The boat doesn't move because the system is closed, meaning all forces are internal. The fans generate a force by pushing air, but that force is directly countered by the reaction force on the boat itself. The net effect of these internal forces is zero, leading to no movement of the boat.

Would it make a difference if the fans were placed in a different location on the boat?

Placing the fans in a different location on the boat would not make a difference if they are still blowing air into the boat's own sails. The principle of conservation of momentum dictates that the internal forces within the system (boat, fans, and sails) will always cancel each other out, resulting in no net movement.

Could this setup work if the boat were in a vacuum or if there was no external air resistance?

Even in a vacuum or without external air resistance, the boat would not move because the issue lies with the internal forces canceling each other out. The absence of external air resistance does not change the fact that the fans' force on the air and the reaction force on the boat neutralize each other.

Is there any way to use fans to propel a boat effectively?

Yes, fans can be used to propel a boat effectively if they are directed to push air backward, away from the boat. This creates a forward thrust due to the reaction force, in accordance with Newton's third law of motion. This is similar to how jet engines or propellers work, where the expulsion of air or water backward propels the vehicle forward.

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