Thanks Wunderer - plenty more coming from Omen!
That’s a great question and there is indeed a torque being induced about the centre of gravity from the off axis downforce generated by the stab.
In a well balanced foil system though, that moment generated by the stab is exactly equal and opposite to the pitching moment from the front wing + the total drag of the system about the centre of mass. So with these moments balance out in level flight the change in the effective COL over the speed range of the foil is very subtle.
Of course, the complication is that for an imperfectly tuned foil system the rate of change of these moments changes at different rates relative to speed. So for most foil setups that are not well tuned the rider will have to shift their weight around to compensate for these different moments.
To get really nuanced there is also a small pitching moment being generated by the stab but fortunately that works in the opposite direction of the front wing’s pitching moment - so it ends up helping stabilize the system along with the stab’s downforce. To really consider foil dynamics I think one needs to shift their thinking from analyzing a static problem to a “set” of problems with variables changing with respect to speed. It’s rather simple as far as calculus goes but the tricky part is not so much the math but actually visualizing and working on these problems over a continuous speed range.
All this to say is that yes, you are correct you when analyzing a foil the torque/moments need to be considered. BUT, for a perfectly tuned system these moments all sum to zero so do not need to be taken into account when thinking about mast position. If your foil is not tuned as such, my goal would be to adjust the tail shim or change your tail to get as close to this point as possible. I think of this as a separate tuning operation from track position, but as you pointed out everything is connected so if your stab tuning is way off there is no “perfect position” for your mast in the tracks since the effective centre of lift wanders aggressively with speed changes.