Wash switches his grip from the rail by the door to the one above it. He then pulls himself up, using his flight ring so his back is pressed against the ceiling. In terms of getting maximum force into a single blow, it's either this or a shoulder tackle, and it's going to be damn near impossible to stay in the ship if he opts for the latter option.

"Three. Two. One."

He deactivates the flight ring and pushes off from the ceiling, swinging forward, legs out front. The split second before his boots connect with Robbie's back: "Mark!"

And Robbie goes, and Wash has to cling to the bar pretty damn hard to keep momentum from carrying him out with Robbie. He reactivates his flight ring, hauls himself back in the ship, and slams on the button to close the door. If this works, then the fight's going to be mostly over by the time he can get down there; hopefully this will have been enough.