George,
Aft-raking the masts might be a mixed bag. The benefits would be
more clear-cut on a cat where you can balance out all the forces,
but less clear-cut on a proa where aft one one shunt is fore on
another.
You could definitely get a great sailboard-like sail shape, but
the build cost would be higher than a straight circular mast, and it
would be harder to trust the boat to tend to itself while on the
hook in a gale.
The bigger issue with moving the COE aft, though, would probably
be rounding up.
Since the boat has to go in both directions, it's useful to move
the COE closer to the center in order to keep the forces on the two
rudder/foils more equal. That would result in better flow over both
foils and cut down on weather helm (and the rudder needed to counter
it).
This is particularly noticeable when going to windward at low
speeds where the foils don't have much to work with. At some point
the forces causing the boat to round up overwhelm the rudders and
the boat stalls.
There's an extensive discussion of this in the forum from
2011.12.30 through 2012.01.10. Rick actually found it was better to
sail with the windward hull to leeward in extremely light winds
because of the rounding up due to: a) Rig COE being aft of the
boat's CLR, and b) drag from the windward hull.
I can see that having mast weight aft would help raise the "bows",
and the canted masts would do this, but I'm not sure that would be
worth moving the COE aft as well.
- Mike