Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 11-02-2013, 06:54   #1
Registered User
 
Tscott8201's Avatar

Join Date: Nov 2012
Location: North Florida
Posts: 104
Settle an argument

Ok, had a friendly argument with my father in law this weekend. Last time we rented a sailboat for a day the instructor commented on the importance of sail trimming due to the fact the sail is basically a wing. Later on that day my father in law brings up that he believes this is all mumbo jumbo and that the "wing effect" is basically oversold. He claims that a perfectly workable sail could be made out of a flat solid sheet of material with no curve and you would get decent performance out of it. Not as good a a curved sail, but almost as good. I told him it might work but would basically be crap and give little to no forward thrust. Who is right?

Tom
__________________

Tscott8201 is offline   Reply With Quote
Old 11-02-2013, 07:04   #2
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 9,662
Re: Settle an argument

Quote:
Originally Posted by Tscott8201 View Post
Ok, had a friendly argument with my father in law this weekend. Last time we rented a sailboat for a day the instructor commented on the importance of sail trimming due to the fact the sail is basically a wing. Later on that day my father in law brings up that he believes this is all mumbo jumbo and that the "wing effect" is basically oversold. He claims that a perfectly workable sail could be made out of a flat solid sheet of material with no curve and you would get decent performance out of it. Not as good a a curved sail, but almost as good. I told him it might work but would basically be crap and give little to no forward thrust. Who is right?

Tom
There are always two sides to a story .
Beating to windward, FIL is 100% wrong
Sailing dead downwind, FIL is 100% right
Anywhere in between, well he is a bit right and a bit wrong.
__________________

__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is online now   Reply With Quote
Old 11-02-2013, 07:32   #3
Registered User

Join Date: Sep 2011
Location: Germany
Boat: secondarily boatless
Posts: 180
Re: Settle an argument

Tom,

2/3 of a sail's force is created by the leeward side, 1/3 by the windward side. That is, if you have laminar flow on both sides. Hence on anything from 40 to about 100 degrees apparent wind it will make a huge difference. Anything above that angle - as the previous poster said, it does not matter as much.

If you are out there you can experience it first hand: Let your mainsail out with wind in the 130 to 150 degrees quadrant. Now if you slowly turn to windward you will experience a very nice kick in the butt the moment the leeward wind goes laminar, and your boat will accelerate a lot (at least mine does). This effect you would be missing.

Another way to convince him: Look at the speed polars of boats. On most of them, you will see a significant increase in speed at the angles listed above.

...if he's still not convinced, ask him to take his next flight in a plane that has flat wings without profile. Unless you power it with a rocket it won't get off the ground...

Oliver
Oliver L. is offline   Reply With Quote
Old 11-02-2013, 07:48   #4
Long Range Cruiser
 
MarkJ's Avatar

Cruisers Forum Supporter

Join Date: Dec 2007
Location: Australian living on "Sea Life" currently in England.
Boat: Beneteau 393 "Sea Life"
Posts: 12,827
Images: 25
Re: Settle an argument

Its a wing.
__________________
Notes on a Circumnavigation.
OurLifeAtSea.com

Somalia Pirates and our Convoy
MarkJ is offline   Reply With Quote
Old 11-02-2013, 07:50   #5
Registered User

Join Date: Apr 2011
Location: vancouver, canada
Boat: hunter 376
Posts: 623
Re: Settle an argument

Hold a teaspoon upside down with a faucet running, then let the outer curve of the teaspoon contact the flow of water. There will be no mistaking the effect, the spoon will be pulled towards the flow. Now try it with a butter knife.
shorebird is offline   Reply With Quote
Old 11-02-2013, 08:14   #6
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Boat: Bestevaer.
Posts: 11,652
Re: Settle an argument

A flat solid sheet with no curve will still work as an (inefficient) wing, developing lift due to the angle of attack.

Directly downwind there is no "wing" effect, but on other points of sail the lift developed by the sail is important.

Its worth rembering that sailboat foils ( keel and rudder) also work primarily as "wings" and many unfortunatly are simple flat plates.
noelex 77 is online now   Reply With Quote
Old 11-02-2013, 08:23   #7
Registered User

Join Date: May 2009
Location: Massachusetts
Boat: 40' Silverton Aftcabin with twin Crusaders
Posts: 1,757
Re: Settle an argument

Quote:
Originally Posted by shorebird View Post
Hold a teaspoon upside down with a faucet running, then let the outer curve of the teaspoon contact the flow of water. There will be no mistaking the effect, the spoon will be pulled towards the flow. Now try it with a butter knife.

THAT SIMPLE TEST IS IMPRESSIVE!

Foggy
foggysail is offline   Reply With Quote
Old 11-02-2013, 08:26   #8
Registered User
 
Tim R.'s Avatar

Join Date: Jul 2012
Location: Portland, Maine
Boat: Caliber 40LRC
Posts: 604
Re: Settle an argument

My FIL is a pilot and we debate many things. This would not be one of them.
__________________
Tim R.
Our Carina is sold
1997 Caliber 40LRC
TKR on a Boat Website
Tim R. is offline   Reply With Quote
Old 11-02-2013, 08:28   #9
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Boat: Bestevaer.
Posts: 11,652
Re: Settle an argument

Quote:
Originally Posted by shorebird View Post
Hold a teaspoon upside down with a faucet running, then let the outer curve of the teaspoon contact the flow of water. There will be no mistaking the effect, the spoon will be pulled towards the flow. Now try it with a butter knife.
That is at 0 angle of attack.
A flat, or symmetrical, plate will still generate lift at a positive angle of attack. If if did not our sailboat rudders would not work.
noelex 77 is online now   Reply With Quote
Old 11-02-2013, 08:35   #10
Registered User
 
stevensuf's Avatar

Join Date: Dec 2010
Location: Algarve, Portugal
Boat: Gib sea 43
Posts: 937
Images: 10
Re: Settle an argument

To those who think the leeward side does work, think again, it goes along with the urban legend that a vacuum sucks the sails along, well sorry a vaccum cannot exert a mechanical force on an object, the pressure difference is what does the work and creates the force.
__________________
http://nicnsteve.blogspot.com/

If the pen is mightier than the sword, then my keyboard must be a nuclear missile!
stevensuf is offline   Reply With Quote
Old 11-02-2013, 08:49   #11
Moderator Emeritus
 
HappyMdRSailor's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: North Mississippi
Boat: 48 Wauquiez Pilot Saloon-C22 Chrysler Sunpiper- 19 Potter-Preparing to cruise w/my girl
Posts: 5,975
Re: Settle an argument

**** SIGH****

Life is too short for silly arguments...
__________________
In the harsh marine environment, something is always in need of repair...

Mai Tai's fix everything...
HappyMdRSailor is offline   Reply With Quote
Old 11-02-2013, 08:51   #12
Moderator
 
carstenb's Avatar

Cruisers Forum Supporter

Join Date: May 2012
Location: At sea in the pacific
Boat: Jeanneau Sun Fast 40.3
Posts: 5,125
Images: 1
Re: Settle an argument

Not quite flat but the guys on mythbusters once built a sailboat entirely from duct tape. They welded up an aluminum frame, covered it with duct tape ..result it was waterproof. Then they raised an aluminum mast and boom and made a sail from duct tape.

Damn thing sailed along quite nicely.

But the rest of the posters are correct. The closer you sail to the wind, the more profile you need
__________________
I must go down to the seas again, to the lonely sea and the sky,
And all I ask is a tall ship and a star to steer her by

www.svcapri.com
carstenb is offline   Reply With Quote
Old 11-02-2013, 09:04   #13
Moderator Emeritus
 
Hudson Force's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Lived aboard & cruised for 45 years,- now on a chair in my walk-in closet.
Boat: Morgan OI 413 1973 - Aythya
Posts: 7,994
Images: 1
Re: Settle an argument

Quote:
Originally Posted by stevensuf View Post
...............with the urban legend that a vacuum sucks the sails along, well sorry a vaccum cannot exert a mechanical force on an object, the pressure difference is what does the work and creates the force.
Sure it's an airfoil or "wing". .....it's also the partial vacuum that is responsible for a degree of the pressure difference dependng upon the point of sail. There's nothing inappropriate with the "suck" description as it identifies this pressure difference,- no urban legend, just semantics.
__________________
Take care and joy, Aythya crew
Hudson Force is offline   Reply With Quote
Old 11-02-2013, 09:22   #14
CF Adviser
 
Bash's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: sausalito
Boat: 14 meter sloop
Posts: 7,260
Re: Settle an argument

Quote:
Originally Posted by CaptForce View Post
Sure it's an airfoil or "wing". .....it's also the partial vacuum that is responsible for a degree of the pressure difference dependng upon the point of sail. There's nothing inappropriate with the "suck" description as it identifies this pressure difference,- no urban legend, just semantics.
The minute you start talking about a partial vacuum, you've entered the rhelm of physics. It doesn't take a great intellectual leap to go from being a creationist or a climate science denier to claiming that a flat sail would work aerodynamically.

The real question isn't science--it's engineering: just how are you going to keep a flat sail flat?
__________________
cruising is entirely about showing up--in boat shoes.
Bash is offline   Reply With Quote
Old 11-02-2013, 09:24   #15
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 9,051
Re: Settle an argument

Quote:
Originally Posted by Wotname View Post
There are always two sides to a story .
Beating to windward, FIL is 100% wrong
Sailing dead downwind, FIL is 100% right
Anywhere in between, well he is a bit right and a bit wrong.
Sailing dead downwind, FIL is 70% right, a cupped shape will provide more drive downwind than a flat plate.
__________________

__________________
Num Me Vexo?
SailboatData
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
Adelie is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Advertise Here


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 04:53.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
×

ShowCase vBulletin Plugins by Drive Thru Online, Inc.