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.
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
>