Thanks for your comments. The rig design, with its significantly swept spreaders, is already a compromise in order to achieve a stiffer mast. With the mast set so far forward, the slot is miniscule and tacking any sail through it would be highly undesirable from a number of perspectives. The inner stay is there to fly heavy weather sails and to oppose its pull with the runners. The rig is ì runner independent ì according to the manufacture.

A Baby stay would be more acceptable but at days end, I believe this is mainly about the mast sections lack of stiffness and perhaps harmonics due to poorly chosen wire fixing locations.

I agree that the lack of forward lowers is contributing to the instability. I would wonder why any designer would not use split lowers except to save cost or for interior space issues associated with a second chain plate.

If the observed motion was only in higher sea conditions my concerns would be elevated. Seeing the mast pumping away in a one foot chop tells me there is something seriously wrong with this rig.