Motion compensating ship personnel transfer gangway - GIF

[mklotz]

I have to agree that the cup is secured to the barrel in some manner. Perhaps they're not trying to show how the cup is balanced on the barrel but rather the fact that the water in the cup doesn't slosh about with the movement of the ship.

MD is dead on with his observation that the viewer should be able to see the ship's deck/gunwale moving about the barrel for it to be impressive. They should have chosen a time when the ship was corkscrewing or at least rolling or pitching.

I spent some time on the bridge of the USS Boston during a gunnery exercise and I can verify that watching those rotationally stable barrels while the ship rolls and pitches around them is a guaranteed method for giving yourself the worst case of seasickness imaginable.