JW is right .. I forgot about the twisting that goes on sometimes.
for a permanant mooring I had:
A plough with a bouy to surface on its tail.... 6 meters of chain to a mushroom ...6 more meters of chain to a swivel block in which was threaded a circular loop of rope (to which there was an eyelet that the boat was tied to) that went to shore, and was fixed there. Sometimes after some heavy tides and winds the pulley would have switched sides so often the boat was hard to pull in as the swivel rotated several times and spiralled the rope, and with a 1" rope.. you needed your weetabix sometimes to haul it in