Overpowered Broad Reach Causing Lee Helm

With my boat overpowered on a broad reach I am experiencing extreme lee helm. Normally, the boat has just the right amount of weather helm.

The wind conditions were in the low 20's during gusts, and I am pretty sure I was burying the lee bow, at which point the helm bias suddenly toggled, pulling to lee.

Any comments on the physics/cause? With the bows going under, the rudders are lifting out of the water, and the boat should want to pivot around the front, pointing to weather. Could this be cavitation or turbulence coming off the centerboards?

Thanks,

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Dan Peake
2003 H17SE
2005 FX1

This would be easier to explain if I knew how to post diagrams but I’ll try. Lee helm occurs when the center of effort for whatever reason moves forward of the center of lateral resistance. When the bow of your boat pitches down as you described the sail plan moves forward. It is also true that the center of lateral resistance will also move forward but you have to consider the direction the force vectors are acting. When sailing down wind the force vectors are acting in a more fore and aft direction than side to side. Viewed from this more fore and aft perspective the center of effort and the center of lateral resistance “appearâ€

Other thoughts:

Where was your crew weight positioned?
What kind of mast rake do you have?
How loose are the side stays?

I recall being on a getaway that had serious lee helm, as soon as the wind came around the back she was ready to spin out and gybe. It was a rental though so I have no idea if it was a set up issue or just something the boat design is prone to in stronger winds.