Thanks all for your help.
We got a local man experienced and resourceful, problem was quickly identified at the output shaft, this enabled us to only take off the gear
Inside we found that the coupling nut had come a bit loose, the worst damage was the coupling fixed to the output shaft by a spline and the had been completely worn (chafed) down to nothing.
We were anchored, unwilling to use the dinghy
to push us into the mariner due to minimal keel
clearance. Feeling vulnerable.
We are repaired now and ready for expected 60 Knot
winds today on east coat of Tassy.
and chip van as mentioned by Chiefcoxain is indeed a treat and social epicentre.
Attached Image is the offending coupling.