Slot effect is indeed a myth in the way many people understand it, much like "maximum hull speed". But there is indeed an interaction between the jib and mainsail that is positive. Surely enough the mainsail is less powerful with a jib in front of it. But the mainsail allows the jib to operate very efficiently at surprisingly low angles of attack. As a result the loses in the mainsail are more then compensated by the gains made by the jib. Another effect of adding the jib is that it makes the mainsail less sensitive to stall. It is easier to keep both jib and mainsail in the groove then just the mainsail. This too is an performance enhancer.

For the remainder I too refer to other posts and threads on this subject. Otherwise book and documents from Arvil Gentry, Frank Bethwaite and Marchaj are a good read. Maybe you can get them at your library ?

The most convincing real life argument that I came across was sailing the F16's myself. I sail and race these both 1-up and 2-up = as a uni-rig and sloop. Interestingly enough the difference between either mode is to small to determine which mode it favoured. But the 2-up have added 60-80 kg to the total weight the boat needs to carry and transport at speed, something must have increased the saildrive therefor and the only difference between the two setups is the jib.

Pointing, speed, distribution of efficiency and other things may well be different between both setups but the end result is surprisingly similar.

I also confirm what Timbo and PTP are saying I too feel that the unis can easily fall of their groove and that the sloop power ahead mostly by speed and despite lower pointing.

Wouter