At the same time, the boat begins to move. So we can bring the same principle to the electromagnetic environment, that is, any space that carries electromagnetic waves: near-Earth space or outer space.
In your acoustic demo, the waves are traveling through mass and causing the mass to move, which propels the boat. In essence, it is a propeller with no moving parts. However, your EM version creates standing waves in empty (devoid of mass) space. How is that the same? I suppose your goal is to use EM to generate momentum, right? Has that ever been demonstrated before?
Look, it's not like you think. There are other processes there. I'll try to explain. Standing waves are created in such a way that the emitters are located at the nodes of the standing waves.
And when we shift the phase, the standing waves begin to move and drag the emitters with them. ...
Now the same principle remains to be repeated on electromagnetic waves, which easily propagate in a space vacuum and will give more thrust.
No one has ever done similar experiments before, since apparently no one could hit upon the idea of this, let's say.
Although, I don't completely understand how the acoustic version works. It seems clear that the momentum is ultimately caused by pushing against the mass of the water, which I think can be demonstrated by completely enclosing the water between the emitters.
But, in the microwave version there is no mass, so where do the momentum come from? There are ideas about creating thrust with lasers, but not in the way you are proposing.