I was picking up my mooring
a couple of days ago and was finding it quite hard to attach the chain to the cleat. Surely if you arranged a motorcycle type chain over a sprocket with two one way sprockets like inside a windlass
and some sort of spring the up and down motion would turn a shaft attached to a generator
the forces are quite high, more than the wind
blowing on a turbine. However I'm sure a generating device to utilise the motion of the mooring
chain is going to be far more complicated and expensive than a simple turbine so no one has done it.