Seahorse Rocking Chair

Now, what does a seahorse use for a rocking chair?
It could just rock in its place--but that's pretty boring,
Especially if we want to be clever now.
So let's invent one! And give it sprockets--or maybe...
Hydraulic! Of course! And powered by ocean currents,
Using vanes that go round--and weights for the rocking!
Wow! That's an invention! We could earn cash like water!
Hey, I'll write to the Patent Office, if only
You will do up those drawings they always want.