Oh and the coin idea would be great, if it weren't such an engineering challenge to create a transparent material strong enough to hold back an ocean of water from flinging into space.
And I don't know if such a boat would float like earth ships, because unlike earth, the deeper in the coin ocean you go, the stronger the centripetal force. I wonder if such a force would practically suck ships down.
Imagine the fish in such an ocean... stuck to the bottom because it takes effort to "climb" up. Swimmers would sink faster than they can float... and boats would have their fishing lines be the straw the breaks the camel's back and starts a chain reation that sucks the whole ship down to the bottom with increasing velocity. Not to mention the force of such a slam on the transparent plating holding in the water.
Sounds like fun!