Why I chose a DUO 660

Start with the understanding that there is no better all around boat. Certain boats may be better for certain uses, so the place to begin in choosing a boat design is to be honest about how you intend to use the boat. Not so easy since sailing for me is aspirational and spiritual so how can more not be better.

So here are my considerations:
My family likes boats if they can jump in the water and play. They will tolerate me simply enjoying to relative silence and peace for awhile (not long).
We like to go crabbing in the summer, but don't like hauling the inflatable and rowing to the crabbing grounds.
Puget Sound is always cold to the touch.
My wife is prone to seasickness, although she is getting better.
I harbor a deep and abiding animosity for convention.
We still have to pay for three college educations so the bank must not be broken
Need to carry the family and hopefully a guest (6 persons although many are small)

So going from considerations to requirements I came up with the following:
Seasickness: Means it needs to either be a catamaran or a trimaran.
Capacity: Trimarans are not much better than monos for people carrying so it pretty much needs to be a catamaran.
$:Besides the build cost the truly scary cost to consider is moorage. In Seattle the sailing season is relatively short. So to avoid paying for moorage in the winter, the boat must be trailerable. That way I can store it either in the driveway or in a much less costly storage yard.
$: Building the boat myself saves money in two ways. First the labor is "free" but also commercially available catamarans seem to be either not trailerable or beach cats. It seems the only way to get the boat I want in the first place is to build it.  Also building myself also has the benefit of spreading the cost over time.
Convention: I really like the bi-plane rig. It puts the structural loads in the place that makes the most sense and is apparently easy to sail with no jib to mess around with when turning.  Ease of sailing is also of great benefit when sailing with only mildly alert kids.

Going from requirements to design selection:
I tried to treat the bi-plane rig as a bonus rather than a requirement since that would have severely limited the choices. Actually it came down to selecting either a Richard Woods or Bernd Kohler design.  I chose Bernd for a few reasons; his designs seemed to weight ease of build more than the Woods designs, he has an easy to detect reputation for after sale support of his designs, and his designs are more unconventional. He has Gunther, Biplane and even "A" frame mast rigs in his stable. With Bernd I could get the right sized, trailerable, easier to build, Bi-plane rigged catamaran and get awesome support.

Other notes:
The 660 uses anti-vortex panels instead of a centerboard or daggerboard.  I read Bernd's paper on them and everything I could find online.  The physics make sense and I think the trade off is that you are accepting a bit more wetted surface area (vs board up) for alot more simplicity. Given that this light catamaran should already be plenty fast I think it is a good trade.

Biplane rig. The reason this is so cool (besides the  easier structure on the boat) is that it allows for a lower heeling moment on the boat for the same sail area.  Basically more of the force on your sails can be put to work propelling the boat instead of tipping it over.

Radical Bay: Schionning Designs of Australia has a Biplane Rig design. While I like the thing I think there are issues. It is too beamy, its been thousands of years of testing that has shown a 2:1 length to beam ratio works for a sea-kindly catamaran.  Not sure why they chucked that out the window.  That is my main complaint, as for my build it is too long for me to build at home and uses strip plank construction. Stip planking while not impossible, is more difficult than I want to deal with now.