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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1. Can a boat move forward if it uses a fan to blow air into its own sails?

No, a boat cannot move forward by using a fan to blow air into its own sails due to the principle of conservation of momentum. When the fan pushes air forward, it exerts an equal and opposite force backwards, which would counteract any forward thrust generated by the sails capturing the wind from the fan.

2. What is the conservation of momentum and how does it apply to this scenario?

The conservation of momentum is a fundamental principle of physics stating that the total momentum of a closed system remains constant if no external forces are acting on it. In the scenario where a fan on a boat blows air into its own sails, the action of the fan pushing air forward and the reaction of the boat (and the air) pushing back are equal and opposite. This balance means that no net forward motion can be achieved because the forces cancel each other out.

3. Are there any real-world applications where a similar principle is effectively used?

While using a fan to blow into a sail on the same vessel is not effective, similar principles are used in other contexts. For example, hovercrafts use fans to lift themselves off the ground by blowing air downwards, creating a cushion of air beneath them. This is a different application of air movement where the reaction force (air pushing against the ground) allows the hovercraft to float above the surface.

4. Could any modifications make this concept work for propelling a boat?

To make the concept work, one would need to alter the system so that the reaction force does not directly oppose the intended direction of motion. One theoretical modification could be to use a separate, external structure to redirect the airflow from the fan in a way that does not directly counteract the boat’s forward motion, perhaps using environmental factors like a fixed installation or another vessel. However, this would complicate the system and might not be practical.

5. What are some effective methods for propelling boats that use wind power?

Effective methods for propelling boats using wind power include traditional sails and kitesurfing rigs. Traditional sailing involves positioning sails so that the wind pushes against them, propelling the boat forward. Kitesurfing uses a large kite controlled by the rider to harness wind power and pull the rider and board across the water. Both methods effectively utilize environmental wind, rather than artificially created wind, to generate propulsion.

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