Robert Biegler: Page 2 of "Twin Foils Experiment" from Messing About in Boats

I'm tempted to ask "Why?" As in "What is the advantage over a conventional proa or catamaran?" Especially at dinner-time at sea.

I only uploaded the second page because I needed that to illustrate a comment was making. The first page states: "The idea originated about three years ago with speculation about how to eliminate totally the heeling moment in sailboats, permitting designs with no need for ballast and with minimal displacement (zero displacement if one could build it) and big, efficient sails standing upright to the wind. In the ideal case, a design might be engineered to produce the world's fastest sailboat."
Note that if you inclined both the leeboard and the rig so that they would be roughly parallel, you would end up with a balance of forces similar to Sailrocket 2. However, there would be a problem with pitch stability of the leeward hull. So I think if high speed is the point, then either the leeward hull and rig should be replaced by a kite, or the windward hull and foil should be replaced by a paravane. The latter would produce a configuration similar to the boat of the Swedish Speedsailing Challenge: Zero displacement is possible of you replaced both hulls and suspended the sailors in between kite and paravane, what Hagedoorn called Ultimate Sailing (see AYRS booklet 114 Ultimate Sailing: Booklets – Amateur Yacht Research Society https://www.ayrs.org/booklets/). This has been put in practice just a few years ago:
Replacing the lines by beams allows the use of more efficient hulls because neither hull needs to stay upright on its own, so I think the practical applications of this configuration would be very limited. One possibility is if you travel with two canoes, you want the option of sailing, but without carrying beams with you. This configuration might be lighter (though I think it would still need some reinforcement where the lines, the rig and the leeboard attach), easier to rig than beams if you are already on the water, and provide more power than putting a sail on each canoe and sailing each as a monohull. Other than that, I see it more as an interesting curiosity.