With respect to the Atlantis paper-

The selected statement on the Cl of sloop rigs is simply wrong.  Cl of a sloop rig can be 1.6 or more.  Also it is not evident that the authors have applied an aspect ratio correction for their sections.  XFOIL is a 2D analysis program so it needs aspect ratio correction.  A NACA 4 series 20% section is capable of a Cl of 1 at an L/D of 50 or a CL of 1.6 at an L/D of 14 as a 2D element having infinite span - these values are similar to the figures given in the paper.  However for an aspect ratio of 3.7 for the wing as fitted to Atlantis the values for a NACA 20% section are Cl of 0.7 at an L/D of 10 and it cannot achieve a Cl of 1.  I expect their ugly section with its flap will be similar once the AR correction is applied.

The rigid wing I tested was a 20% NACA 4 section with an aspect ratio of 4.  The only white knuckle part of using that was trying to get out of a rhythmic roll when tacking in light wind.  The rest of the time I was sitting around similar to the crew on Atlantis in their photo.

Have a look at this video:

Same boat as Atlantis but with useful size sails.  The size of the waves and the lack of cresting indicates wind below 5m/s (10kts).  Now compare that with the photo in Figure 1 of the paper.  Clearly there is a fresh breeze as their charted 6m/s indicates but the boat speed is hardly white-knuckled excitement.  That is the result of thinking that a wing 1/3rd the area of a a sloop rig can achieve the same results - it is laughable. 

Anyone set on using a wing on a cruising boat should plan on carrying two or three of them, maybe of different sizes, and have a system to easily drop them onto the deck in a secure position that does not add substantially to the windage of the boat once they are stowed. 

 

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