That would be a problem. I saw the rigid-wing boats and thought there wasn’t a limitation…
From the comment above, it appears that all that is limited is the spar itself, fairings around the spar are allowed (?)
As you’ve noted, one key parameter is the leading-edge radius. To get any improvement that needs to be somewhat smaller than the max width of the mast/wing (i.e. the leading edge of the rig needs to look “wing like”).
One way to do this is with ribs or some other non-structural support that shapes the sail envelope in front of the (structural) mast. That gives you all be benefit of the wing-mast but still retains the 12mm dia. tubular mast. Most classes that allow sails made from more than one layer prohibit this for exactly that reason.
A much simpler alternative is to choose a non-rotating mast shape that generates the least interference.
Arvel Gentry did quite a bit of work in this area:
http://arvelgentry.jimdo.com/articles/
In particular there are three articles that discuss this problem:
[ul]
[li]Design of the Courageous Mast
[/li][li]Studies of Mast Section Aerodynamics
[/li][li]Low Drag Star Mast
[/li][/ul]
One “take home” from the Gentry articles is that an elliptical mast gives you much of the benefit of the more tailored sections.
I believe Frank Bethwaite also talks about this issue in the section on designing the mast for the Tasar in “High Performance Sailing”.
Cheers,
Geoff S.