I was playing 17w47b, and when I sailed in a boat I could move forward just fine. But when I turned the boat, the rotation visual looked like the game was playing at 20 frames per second (fps). If I turn my head while in a boat (move the mouse left and right) then I can see left and right normally. But if I turn the boat (use arrow keys to turn the boat), my view with the boat rotation looks like it's happening at 20fps. It's as if my view is updated at the same rate as the server code, instead of having linear interpolation performed in the client code to smooth my view.