Another one for the physicists

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jimboalee

New Member
Location
Solihull
Twas on the good ship Venus,
By God you should have seen us.
The Boatswain's name was Carter,
'Carter the farter'.

When the wind didn't blow,
and the ship wouldn't go,
it took Carter the farter to start her.


This is crap because if the source of the air's movement is standing on the same object as the sail ( the boat's deck ), forces cancel and there is no movement.
 

slowmotion

Quite dreadful
Location
lost somewhere
Piemaster said:
As above its all about vectors. .

I can see that a yacht can go faster in the direction it is going than the velocity component of the wind in that direction. For example, if the wind is coming at right angles to the boat's heading, there is zero velocity component of the wind in that direction, but the boat still moves ahead while reaching. What confuses me is this...can the boat go faster than the windspeed itself? My guess is that it can't.

I may not have expressed this very well.
 

slowmotion

Quite dreadful
Location
lost somewhere
Piemaster said:
As above its all about vectors. Think about the wind blowing on the sail, the pressure on one side is greater than the other. Pressure=force /area (of the sail). So what could be a relatively small pressure differential on the sail area can produce a large force which is converted into forward motion by the shape of the hull.
BTW land and ice yachts can achieve 5-6 times the wind speed.

Sorry Piemaster, I reread your post, and I can sort of see the concept.
 

slowmotion

Quite dreadful
Location
lost somewhere
Coco said:
click on my second link above for a child friendly explanation. :laugh:

I feel suitably chastised! Naughty Step for me, I guess.

OK, this a bit OT, but that link does kind of suggest that a glider with large aerofoil wings could make progress over the ground even when presented with a headwind. That is counter-intuitive. Would it have to swoop up and down to do that?
 

Coco

Well-Known Member
Location
Glasgow
Do you mean wing as in horizontal aerofoil? If it was placed in a headwind then it would generate lift and go up the way, not forward. But don't forget that gravity has a big influence on gliders :laugh:
 
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^
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Here is a boat heading east with the wind blowing up from the south. The sail is running from say 11 to 5 on a clock

Wind will be faster than the boat as at that angle (disregard drag on the boat) the wind will travel up faster than the boat goes east.

Now imagine the sail at a steeper angle of say 10 to 4 on a clock.
Assuming the wind blows the boat without any other loss the boat will move more east than the wind move up.

Then once it is moving at a decent speed the angle can be increased further.


On the point of the wind being behind you, dont they just head in a different direction off to one side then the other. The increase in speed should more than make up for the greater distance.
 
slowmotion said:
I feel suitably chastised! Naughty Step for me, I guess.

OK, this a bit OT, but that link does kind of suggest that a glider with large aerofoil wings could make progress over the ground even when presented with a headwind. That is counter-intuitive. Would it have to swoop up and down to do that?

There are a few boats that use a rigid aerofoil as a 'sail' such as the 'sailrocket'. Not a conventional boat, but it floats, and has a sail of sorts so guess it counts.
 

slowmotion

Quite dreadful
Location
lost somewhere
Blooming Heck! I'm still lagging on the physics front, but that looks like a whole lot of fun. Maybe I could rig a huge kite to a 22 foot Hurley, and look "well hard" off Falmouth.
 

Fnaar

Smutmaster General
Location
Thumberland
Coco said:
Do you mean wing as in horizontal aerofoil? If it was placed in a headwind then it would generate lift and go up the way, not forward. But don't forget that gravity has a big influence on gliders :smile:

What if it was a proper plane, rolling along on a treadmill? Would it take off?* :smile::biggrin::smile::biggrin::smile::smile::tongue::smile::tongue::smile:;):smile:


(*one for the Cycling Plus renegades)
 
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