Phils Rig School continued...

How precisely do you plan on transfering the load between the two tubes? I'm strugling to picture exactly what you mean if I'm honest, but unless the two are bonded together you will not get any load transfered between them until they touch, and then you will have to find a very cleaver way of them not chafing through one another over time.  (I can't quite remember but I think there is something similar explored in 'High Performace Sailing', one of Frank's NS14 experements - I'll look it up tonight)

Really could do with some pictures to help with this one.  It sounds like you are trying to have a one size fits all outer and just swap the middle for different boats (am I right?).  If so, why? Surely, you of all people would want something that was designed from the outset to be bespoke foor your type of boat?

As for your comment on 49er rigs, I take it you mean the old ones with the glass-fibre top sections, and for you to say they 'bend curves are all over the place' is something that I would take some exception to.  But it is an argument we have had before and there is no need to repeat, I will agree to disagree with you there. 

It sounds a bit like you have missed the point of rigging.  Why go to the effort of designing two masts when you can have only one and then use a few bits of string (wire) to stiffen it up externally.  The further the support is from the centre of the structure the more efficient it is, so it can ber lighter and thinner, to create an inner mast tube which "is restrained from bending in any other direction than fore and aft" is in the real world impossible, the heeling force from the rig is far higher than the driving force (upwind at least) so short of using a solid scaffolding bar how do you plan on stopping it bend to leeward? 

I don't think tuning a rig is difficult, I know exactly what I am looking for when I do it, and no on my boat where I have shrouds, caps, forstay, heel position, and chocking to play with, as well as spreader lengths and deflection I have it set up with one position for winds of 0-25knots (I rake the mast back a touch beyond that, but rarely use it).  What you are trying to achieve is a neutral helm, can you sail th eboat upright, upwind, in a straight line without having to steer? all you are trying to do is balance the rig and foils.  Chapter and verse has been written on how to go about doing this already, by far smarter people that I, the basic principles are the same on all boats, the implementation changes due to sail plan and deck layout, but it is just variations on a theme.