As you can clearly see in this photo below, there are no mussels attached to the rudder or propeller.
Actually, you can't see any such thing in this photo. But take my word for it there are no mussels. Or rather, some seaweed is growing on the rudder and propeller -- it's amazing how fast it grows -- and I'll have to get the boat out for a run to swish off the seaweed so I can see underneath. But I'm still feeling hopeful.