Hello, I live in an area with large tides averaging 15 ft, twice daily. The city has a huge floating dock system in a large harbor held in place by fixed steel pilings. I have no idea what the weight is but it is a huge harbor housing a large fishing and personal use fleet. The docks are wood and concrete are obviously enormously heavy. Heres the question. It would take a lot of power to lift and lower this huge mass up and down 15 ft (4.72M) twice daily so could that energy conversely be harnessed? So far as I can tell, all ideas for tidal energy are essentially versions of underwater wind farms, with many inherent limitations such as salt water corrosion and marine wildlife mortality. What I am picturing here is a small power plant on each or many of the fixed pilings with all mechanics out of the water. The question is, is this physically possible harness electrical energy from a large mass moving at a VERY slow pace? Any ideas? Is this an impossible thought. I am a layperson (healthcare worker) so answers in dummy speak or direction to resources would be helpful. I fully expect someone to say this would require mile wide cog or something but I have to ask. Thanks!