Rotating About a Curving Axis

I’m trying to make a gradually-widening spiral that rotates about a curved axis, as if it’s a rope that you attached to the propeller of a boat that’s turning, thus both twirling and curving to the side if that makes sense:


The animation needs to be Unity-exportable, such that you can average its right-bending twirl animation halfway with its left in a blend tree, the result twirling straight up and down:


Pending a way to also rotate around that nurbs spine, I for the time being abandoned the bone constraint and procedurally arranged a string of bones into the spiralling shape, which appeared more plausible as it will also need to undergo other dynamic motions.

While I can pose it alright as you can see, the mathematics of rotating it correctly and blending it properly in Unity are getting hairy.

Any ideas?

Can you use Bézier curves in Unity, if so that would be my preferred method, you can then use this curve to distort a mesh or provide a path for a mesh to travel down.

Cheers, Clock-down-under.