If you're asking the difference between the ARC boats and the Nacra boats, there is plenty. Beam width (12' for ARC 20 and 22 vs. 8'6" for Nacra) immediately comes to mind. That's huge when it comes to handling weather, as well as square footage for the family (cooler, radio, etc.). The only drawback is that you can't trailer something 12' wide, so you would have to assemble it if you travel a lot.

As you can see, a well sailed ARC is competitive (BRoberts won Steeplechase two weeks ago) in distance (and has a "sweet" rating), and is (according to the designer's view) built solid (the hole in that red one at Steeplechase notwithstanding - no boat is bulletproof).

Not much of a fleet of ARC here in FL, but they are out there...