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11-02-2013, 09:31
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#16
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Moderator
Join Date: Jul 2007
Boat: Bestevaer.
Posts: 14,678
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Re: Settle an argument
Quote:
Originally Posted by Bash
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?
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A winged sail would be a good comparison.
These are not flat, but are a symmetrical aerofoil, which has equal camber on both sides, like flat sheet.
You could build a winged sail out of a flat sheet, I am not sure why you want too, but sometimes in settling an argument reason does not play a role
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11-02-2013, 09:31
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#17
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Marine Service Provider
Join Date: Oct 2006
Location: Eastern Shore, MD
Boat: Camper Nicholson 44 Ketch
Posts: 2,060
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Re: Settle an argument
Is your FIL a member of the Flat Earth Society??
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11-02-2013, 09:35
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#18
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Registered User
Join Date: Nov 2012
Location: North Florida
Posts: 104
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I should clarify we are discussing sailing into the wind not a down wind run.
Tom
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11-02-2013, 09:37
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#19
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Registered User
Join Date: Aug 2006
Location: Skagit City, WA
Posts: 25,477
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Re: Settle an argument
Never argue with the FIL, even when he's wrong as in this case!
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard
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11-02-2013, 09:53
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#20
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Registered User
Join Date: Dec 2006
Location: Seattle
Boat: Cal 40 (sold). Still have a Hobie 20
Posts: 2,944
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Re: Settle an argument
Quote:
Originally Posted by Tscott8201
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
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If a curved wing surface is required to make lift in one direction explain to me how planes fly upside down.
Arvel Gentry, Boeing Engineer, sailor, using a flat plate to explain how lift is generated.
The Origins of Lift
Proper wing shape important, yes. Proper trim important, yes. But we're underpowered half the time due to lack of wind. Also, trying to sail upwind most of the force of the sail is pulling us in a direction we don't want to go, so doing everything possible to maximize the lift to drag ratio makes a big difference in how well you go to weather. You would still go to weather with a flat plate, just slower.
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11-02-2013, 10:09
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#21
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,420
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Re: Settle an argument
Quote:
Originally Posted by Adelie
Sailing dead downwind, FIL is 70% right, a cupped shape will provide more drive downwind than a flat plate.
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Not if their areas are equal.
b.
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11-02-2013, 10:12
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#22
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 20,489
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Re: Settle an argument
Quote:
Originally Posted by barnakiel
Not if their areas are equal.
b.
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Even with equal areas and the same projected shape the flat plate will have less drive than the cupped plate.
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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11-02-2013, 10:19
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#23
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Registered User
Join Date: Dec 2008
Location: St. Georges, Bda
Boat: Rhodes Reliant 41ft
Posts: 4,131
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Re: Settle an argument
F-104 Starfighter.
__________________
so many projects--so little time !!
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11-02-2013, 10:22
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#24
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 20,489
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Re: Settle an argument
Quote:
Originally Posted by Blue Stocking
F-104 Starfighter.
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Huh?!?
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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11-02-2013, 10:23
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#25
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Registered User
Join Date: Dec 2012
Location: New Orleans
Boat: Bruce Roberts 44 Ofshore
Posts: 2,842
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Re: Settle an argument
Downwind, with a perfectly flat sail, airflow would just burble around the edges. With some curve, you will get a small amount of laminar airflow. The more, the more. Look at a spinnaker as an example.
Want to test it? Make a plywood sail, with 2x4 strongbacks to keep it flat. The boat will sail but in a pretty sucky fashion. Performance will be abyssmally underwhelming at any point of sail, worse in some than others but always awful.
Wing, schming. Don't think wing-shaped. Think SAIL-shaped. But it still needs shape.
__________________
GrowleyMonster
1979 Bruce Roberts Offshore 44, BRUTE FORCE
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11-02-2013, 10:24
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#26
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 20,489
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Re: Settle an argument
Quote:
Originally Posted by barnakiel
Not if their areas are equal.
b.
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A thin disk has a Drag Coefficient of 1.1 vs a hollow semi-sphere cupping the wind which has a Drag Coefficient of 1.42. It is reasonable to assume that a slightly cupped disk has a Cd greater than 1.1 and less than 1.42.
Drag Coefficient
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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11-02-2013, 10:27
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#27
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Registered User
Join Date: Dec 2006
Location: Seattle
Boat: Cal 40 (sold). Still have a Hobie 20
Posts: 2,944
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Re: Settle an argument
Quote:
Originally Posted by Blue Stocking
F-104 Starfighter.
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That's cheating. It's almost a rocket with a pilot and control surfaces strapped on. I remember that they had covers for the knife edge leading edge to not hurt people.
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11-02-2013, 10:35
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#28
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Registered User
Join Date: May 2011
Location: Lake Ont
Posts: 8,547
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Re: Settle an argument
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11-02-2013, 10:36
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#29
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Registered User
Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,420
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Re: Settle an argument
Quote:
Originally Posted by Adelie
Even with equal areas and the same projected shape the flat plate will have less drive than the cupped plate.
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Proof?
b.
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11-02-2013, 10:40
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#30
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 20,489
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Re: Settle an argument
Quote:
Originally Posted by barnakiel
Proof?
b.
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Two posts further along: http://www.cruisersforum.com/forums/...ml#post1154286
__________________
Num Me Vexo?
For all of your celestial navigation questions: https://navlist.net/
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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