A quick - very quick check revealed that three bolts holding a collet supporting the mast at deck level had sheared, leaving the mast waving merrily at the passing waves. We rapidly brought down all sail to prevent a rig collapse and surveyed the damage. Clearly, competitive sailing was out, so sadly, our race was over. We discussed the possibility of a repair at Kinsale, but it looks like a mast-out job and, since the boat is on charter, with the owners on another boat, we were not in a position to get agreement for repair.
So, we are now retired from the race, slowly motoring our way back to plymouth - probably via Penzance to pick up more fuel.
The crew have been brilliant - although everyone is clearly disappointed, spirits are good as we work our way through Emily's cake.