Physics of Sailing - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > Skills and Seamanship > Learning to Sail
 Not a Member? 


Like Tree5Likes
Reply
 
LinkBack Thread Tools
  #1  
Old 12-29-2013
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,281
Thanks: 5
Thanked 27 Times in 18 Posts
Rep Power: 11
billyruffn will become famous soon enough
Physics of Sailing

Found this on a surfing expedition today. Thought it might be of interest to some in present company.


Happy New Year
Reply With Quote Share with Facebook
The Following 5 Users Say Thank You to billyruffn For This Useful Post:
arknoah (01-02-2014), Corto Maltese (12-30-2013), jagpfd (03-16-2014), robert lawson-smith (01-02-2014), sailortjk1 (12-31-2013)
  #2  
Old 12-29-2013
Member
 
Join Date: Dec 2013
Posts: 46
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 0
Torch is on a distinguished road
Re: Physics of Sailing

Good stuff, thanks for sharing.
Reply With Quote Share with Facebook
  #3  
Old 12-29-2013
Barquito's Avatar
Barquito
 
Join Date: Dec 2007
Location: Madison, WI
Posts: 1,965
Thanks: 0
Thanked 14 Times in 14 Posts
Rep Power: 7
Barquito is on a distinguished road
Re: Physics of Sailing

I really don't know anything about sail physics, but, that was pretty simplified. I think they got the bit about luffing all wrong (7:43). They said luffing is like an airplane wing stalling. I would think that would happen at a high angle of attack, not at zero angle of attack. Regardless, those are some nice shots of sailboats doing their stuff. Any boats we know in there?
nolatom and Seaduction like this.
__________________
Bristol 27
Cirque
Reply With Quote Share with Facebook
  #4  
Old 12-29-2013
Member
 
Join Date: Dec 2013
Posts: 46
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 0
Torch is on a distinguished road
Re: Physics of Sailing

An airplane wing stalls when it looses its lift. So, from that perspective a sail luffing is a good analogy. But your right that an airplane wing looses it's lift due to insufficient wind speed over it's leading edge which is not what a sail does. Most sails, unlike airplane wings, are not rigid so it's a challenge to compare the two in all circumstances.
Reply With Quote Share with Facebook
  #5  
Old 12-29-2013
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,281
Thanks: 5
Thanked 27 Times in 18 Posts
Rep Power: 11
billyruffn will become famous soon enough
Re: Physics of Sailing

Quote:
Originally Posted by Barquito View Post
I think they got the bit about luffing all wrong (7:43). They said luffing is like an airplane wing stalling. I would think that would happen at a high angle of attack, not at zero angle of attack.
I think you're right. Good catch. I think the situation they were showing in the tank was the equivalent of an over trimmed main sail, which is like a stall and nothing like a luff...where you're decreasing the angle of attack. Right?

I did like the bit about not having to understand all the physics to make the boat go. It helps, but is not essential.

Last edited by billyruffn; 12-30-2013 at 12:05 AM.
Reply With Quote Share with Facebook
  #6  
Old 12-30-2013
Corto Maltese's Avatar
Junior Member
 
Join Date: Mar 2012
Location: Spain
Posts: 13
Thanks: 7
Thanked 0 Times in 0 Posts
Rep Power: 0
Corto Maltese is on a distinguished road
Re: Physics of Sailing

Good stuff, thanks
Reply With Quote Share with Facebook
  #7  
Old 12-30-2013
capt vimes's Avatar
Senior Member
 
Join Date: Dec 2013
Posts: 611
Thanks: 7
Thanked 16 Times in 16 Posts
Rep Power: 1
capt vimes is on a distinguished road
Re: Physics of Sailing

Quote:
Originally Posted by Torch View Post
An airplane wing stalls when it looses its lift. So, from that perspective a sail luffing is a good analogy. But your right that an airplane wing looses it's lift due to insufficient wind speed over it's leading edge which is not what a sail does. Most sails, unlike airplane wings, are not rigid so it's a challenge to compare the two in all circumstances.
Stalling of a wing has little to do with wind speed as you described it...
An airplane wing stalls when the angle of attack gets to big for the speed...
What happens essentially is that the airflow separates from the upper wing, creating turbulences and thus eliminating lift, because lift is only produced in a laminar flow situation...
So the insufficient wind speed at the leading edge has nothing to do with it... Speed only factors in in terms of that the maximum angle of attack decreases with speed for a given, solid foil or wing...
SchockT likes this.

Last edited by capt vimes; 12-30-2013 at 06:09 AM.
Reply With Quote Share with Facebook
  #8  
Old 12-30-2013
svHyLyte's Avatar
Old as Dirt!
 
Join Date: Nov 2008
Location: Tampa Bay Area
Posts: 2,717
Thanks: 13
Thanked 104 Times in 99 Posts
Rep Power: 6
svHyLyte is on a distinguished road
Re: Physics of Sailing

Quote:
Originally Posted by capt vimes View Post
Stalling of a wing has little to do with wind speed as you described it...
An airplane wing stalls when the angle of attack gets to big for the speed...
What happens essentially is that the airflow separates from the upper wing, creating turbulences and thus eliminating lift, because lift is only produced in a laminar flow situation...
So the insufficient wind speed at the leading edge has nothing to do with it... Speed only factors in in terms of that the maximum angle of attack decreases with speed for a given, solid foil or wing...
Hence the old Saw: "When in Doubt, Let it Out".

Over trimming can also lead to excessive weather helm requiring a lot of rudder which can lead to stalling the rudder/keel.

N'any case, I think the film is quite interesting and informative.
__________________
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
Reply With Quote Share with Facebook
  #9  
Old 12-30-2013
Senior Member
 
Join Date: Jun 2005
Location: New Orleans
Posts: 1,869
Thanks: 6
Thanked 23 Times in 21 Posts
Rep Power: 10
nolatom will become famous soon enough
Re: Physics of Sailing

I too think of stall on, say, a jib as having too steep an angle of attack despite a nice curved airfoil, so I have to ease the airfoil out to give the wind an easier job of turning the "outside corner" of the foil just aft of the headstay.

Easing out too far and creating a true luff isn't 'stall' to me, but rather the sudden nonexistence of the "floppy foil" itself, which instead becomes a "flag/rag/drag" and no longer a foil/wing at all.
Reply With Quote Share with Facebook
  #10  
Old 12-31-2013
Barquito's Avatar
Barquito
 
Join Date: Dec 2007
Location: Madison, WI
Posts: 1,965
Thanks: 0
Thanked 14 Times in 14 Posts
Rep Power: 7
Barquito is on a distinguished road
Re: Physics of Sailing

Quote:
I did like the bit about not having to understand all the physics to make the boat go. It helps, but is not essential.
Especially since the physicists don't even agree (or know) how sail aerodynamics work. From a pedagogical perspective I think it depends on your learning style and background. It is OK with me to describe sailing with force vectors. But, for some this might result in needless blank stares.
__________________
Bristol 27
Cirque
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
The physics of a mooring ball... MedSailor General Discussion (sailing related) 11 04-01-2013 10:59 AM
IB Extended Essay on physics in sailing... help!!! yashgore SailNet FAQ 6 08-06-2011 09:31 AM
The Physics of Railmeat smackdaddy Racing 50 01-08-2011 09:33 PM
Physics of the random overhand sneuman General Discussion (sailing related) 6 03-12-2005 02:20 PM


All times are GMT -4. The time now is 08:00 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.