Actually sail interaction is quite complex issue. If you want to study the issue read Arvel Gentry's work at www.arvelgentry.com and especially the article "The Aerodynamics of the Sail Interaction". His finding was that the jib provides more lift than main since the slot between sails slows the airflow between sails and makes the air move faster on the windward side of the jib. At the same time the slowed flow in the slot makes it possible to sheet the main harder and still keep the flow attached.
Arto
BTW the article was published in 1971 and still most sailors explain the slot effect based on exactly opposite theory not supported by wind tunnel tests.
From: Rob Denney <harryproa@gmail.com>
To: harryproa@yahoogroups.com.au
Sent: Saturday, August 27, 2011 8:54 AM
Subject: Re: [harryproa] air and fore and aft sails
To: harryproa@yahoogroups.com.au
Sent: Saturday, August 27, 2011 8:54 AM
Subject: Re: [harryproa] air and fore and aft sails
My understanding is that the trailling boat is sailing in turbulent air, which has had a significant amount of energy removed and has been altered in direction causing the trailling boat to sail in a header. This is also the case with a jib, but perhaps because of the proximity to the main, this adds to drive. No idea when the seperation becomes enough to lose the slot effect, but pretty sure it is less than a boat length. I am sure Tom or Rick can explain it better.
rob
On Sat, Aug 27, 2011 at 8:35 AM, LucD <lucjdekeyser@telenet.be> wrote:
Intuitive physics of air plays tricks on us and our explanations. It is often cause for unfounded disagreements. I do not see a fundamental difference between the interference between two consecutive sail surfaces except that in some configuration and orientation to wind and windspeed, the interferences are positive or negative compared to some other configuration. I can imagine two boats following each other at the right configurations strengthening each other's performance just as the main and jib can influence each other positively. Of course, the former will be more difficult to demonstrate consistently in free sailing circumstances. Or does my intuition play tricks on me?
Luc
--- In harryproa@yahoogroups.com.au, Rob Denney <harryproa@...> wrote:
>
... On the schooner rigged
> Elementarry, the front rig was much more powerful than the back, same as a
> main/jib. This is either because they help each other (same as main and
> jib), or because the aft one is in bad air, same as when you follow another
> boat close astern). I suspect the latter, but hope for the former, so put
> them close together.
>
...
>
> rob
>
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