I used to bolt a chunk of brass to the base of my Leica when I shot theatre. Worked as described.

Helen: I was kidding about the gyro stabilizer.
Peter: I was kidding about the gyro stablizer.

There is always a place where it pays to change film size. When the water's too deep to sink legs, then 120 gives you almost two stop of shutter speed, which gives you 1/4 the motion blur.

On the other hand, with judicious development, in particular reduced agitation, you can always push TMY 2 stops ! No real grain increase, while keeping a long straight line !