Prop Shaft

[gn7]

I think this is what Bob is saying.
Attachment 39625

Pretty much. Its not a lot different when the prop is submerged, except the top down is adding thrust. But its easy to see the effects of the lower force on the up swing.
If it was equal, there would no to very little lift because it would simply counter the down swing that creates the lift. And the prop wouldn't "swim" and there would no benefit to running a circle boat off the snout, it would be neutral.