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 Post subject: how sails work project
PostPosted: Wed May 14, 2014 3:59 pm 
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I am getting my us sailing instructors license and I have to do a chalk talk, land drill and a water drill about how sails work. the chalk talk part is easy enough but I'm having a hard time thinking about what I can do for the land and water drill part. do you guys have a idea about what land and water drill I can do to show how sails work?
thanks
angelo

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PostPosted: Wed May 14, 2014 6:56 pm 
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How old is your target audience?

That will determine how complicated / sophisticated the drills are.


Last edited by MBounds on Wed May 14, 2014 7:27 pm, edited 1 time in total.

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PostPosted: Wed May 14, 2014 7:01 pm 
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It's an airfoil, with similar (yet different) foils in the water (rudder and dagger board). Look up aircraft wing and go from there. It's pretty much the same thing.


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PostPosted: Thu May 15, 2014 6:19 am 
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They are adults and teenagers.

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PostPosted: Thu May 15, 2014 8:04 am 
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Take an electric fan, use a 1/4" dowel as a mast, use a snorter piece as the boom, make you a sail. Hold it in front of the fan aiming towards the fan, no reaction, then start to turn it, and see the reaction............. get my point.


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PostPosted: Thu May 15, 2014 6:17 pm 
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Sounds like you need some prop ideas: fly a kite, remote control model sailboat, paper airplanes, balsa wood airplane glider. Just trying to add to the pool of Ideas.

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PostPosted: Sat May 17, 2014 6:09 pm 
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Tom Kirkman wrote:
It's an airfoil, with similar (yet different) foils in the water (rudder and dagger board). Look up aircraft wing and go from there. It's pretty much the same thing.
Technically, a sail is not an airfoil - a sail is a camber line.
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One thing you could demonstrate is Bernoulli's principle - hold two pieces of paper close together and blow between them - get people to guess what will happen.
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The papers will come together, not blow apart.


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PostPosted: Tue May 20, 2014 10:47 am 
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Just tell them that main sails work due to magic and rudders and jibs use magnets. Mentioning the Coriolis effect will get you bonus points.

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PostPosted: Tue May 20, 2014 12:26 pm 
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Probably the most useful tidbits for me are the way the sails and hull shape/keel/dagger boards work together to get motion, like squeezing a watermelon seed between your fingers to shoot them across the room. A sail without anything to press against under the water gives you no forward progress, you need both to move in any direction other than just downwind.

Another thing that really surprised me was how much of a shape you created in the sail and how that pulls you forward. Before realizing that, I thought that the sail was just flat.

I have to believe that there are great youtube videos now that really show you whats happening.

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PostPosted: Tue May 20, 2014 4:15 pm 
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ASDASC wrote:
I have to believe that there are great youtube videos now that really show you whats happening.
Do a Google search for "sail computational fluid dynamics."
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Check out the vortex created by flow escaping under the boom. Vorticies = induced drag.


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PostPosted: Tue May 20, 2014 4:22 pm 
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MBounds wrote:
Check out the vortex created by flow escaping under the boom. Vorticies = induced drag.



Not to highjack another thread... IMO this is also one of the reasons a low profile raked rig is faster on a H16... :) My theory is the tramp acts as a winglet of sorts from the jib being run so low, and helps clean up the air flow around the front crossbar and gets the boom into already disturbed air instead of giving it clean stuff to mess up.


Off to teach upwind sailing to newbies tonight at a Fleet 297 Hobie U! Armed with a piece a paper.. :mrgreen:


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PostPosted: Tue May 20, 2014 5:14 pm 
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ronholm wrote:
MBounds wrote:
Check out the vortex created by flow escaping under the boom. Vorticies = induced drag.

Not to highjack another thread... IMO this is also one of the reasons a low profile raked rig is faster on a H16... :) My theory is the tramp acts as a winglet of sorts from the jib being run so low, and helps clean up the air flow around the front crossbar and gets the boom into already disturbed air instead of giving it clean stuff to mess up.
Minimizing the space between the boom and the trampoline reduces induced drag, but the jib really doesn't come into play WRT that.

Google "end-plate effect" - NASA did studies on this in the 1950s.


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PostPosted: Tue May 20, 2014 8:04 pm 
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Thanks Matt. Googling now!

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