[Sammi]

What type of mechanical wear are you thinking of?

I can think of a propeller and generator, but those are solved problems. This is just a boat with a propeller. Only instead of using the generator as an engine to spin the propeller, the tides spin the propeller which generates power in the generator.

Steering is also a solved boat problem.

Then there's the tether and anchor. This is the reason it swims in a figure 8, instead of it just being a propellar anchored straight to the seabed. So the "pulling" force is actually mostly to the sides instead of directly on the tether and anchor.

[DrNosferatu]

That swinging tether immersed in saltwater(!) will have to work miracles.

[Sammi]

I'm trying to see what prior art we can find on the internet on tethers and anchors used in fish farming and offshore oil industry, but I'm not finding many sources.