At anchor in our X in Poole harbour, tide approx 1-2 knots and wind 12mph. We were the only boat dancing around while all the other keel boats were standing still so I tried every conceivable combination to try sort it out.

Best solution came by partly dropping the centreboard (releasing the rope by 160mm so that the board acted as a long keel). Had the engine and one (port) rudder fully down. The anchor rope was over the bow but held to the towing eye with a snubber. The dancing virtually stopped. Dropping or raising the centreboard fully brought back the dance.

It seems that the solution is to keep the board close to the hull. I would be interested to see if anyone else can replicate this. Not sure how to solve it with an M since it has a daggerboard.