It always suprises me that when every time a M20 does well in a race (not too often) that this is claimed to be the result of being an uni-rig while at the same time it is also about 150 lbs lighter then as good as all its competitors, 2 feet wider and at least 3 feet taller then its competitors. One would think that these differences make an impact as well, especially in light winds were a tall rig is many times more powered-up because of the laminair wind speed winds distribution with height. See the picture below.





Note how in laminair winds a boat with a 10 meter tall mast cat harvest 30% more energy then a 9 mtr tall rig. That is how much difference a single meter of mast length can make (in the extreme).


The only way to get a real answer on this question is to fit identical boats with these different rigs and compare them over a wide range of conditions. Actually that would require four different rigs as there four different ways how you equalize the uni-rig to a sloop rig in the important parameters.

-1- The uni-rig mainsail and mast are identical to the those of the sloop that in turn has an added jib. (Uni has less overall sail area)

-2- The uni-rig is identical in everything like the mast length but can move all area of the jib into its mainsail. (uni-rig has same sail area with same height and much more heeling moment)

-3- The uni-rig is identical in every like the mast length but with that amount of sail area added in its mainsail so that it has the same heeling moment as the sloop rig.

-4- The uni-rig adjusted both the mast length and sailarea to arrive at the same heeling moment as the sloop rig but now in the most efficient way performance wise.


Pretty much options -1- and -3- are slower then the sloop rig or at best just as fast in narrow speed grooves. Option -4- will not be much faster then option -3- at all, there is too little difference there. Option -2- will be faster in light winds (below 5 knots) but quite loose alot of speed when the winds turn turbulant (above 5 knots), it will loose more and more performance with increasing winds due to having significantly more heeling moment then the alternative sloop rig. Pointing will go out the door very quickly as well when the leech has to be slackened to depower the top of the sail.

Without a spinnaker all uni options are significantly less performant on downwind legs. This takes a large chunck out of their upwind advantage if it doesn't totally correct or overcorrect for it.

The only exceptions that can make unis more performant around a course is when the overall total amount of sail area is limited to a sufficiently low amount so that it is only practical to make one single sail out of it. Sloops really come into play when this limit is increased to a level where it is no longer practical to put all the area into a single sail.

That is the whole scientific founded story.

Wouter