A sail can't run directly upwind because the air flow is collinear to the direction of travel so there is no percentage of force available to propel the boat directly up wind but mine can sail at around 3/4 of true wind speed at an AOA of 30° to apparent wind.
My thinking is.
The land yacht changes the AOA over the propeller by altering the mechanical drive by 90°, and then again with the pitch of the propeller.
I have waterflow at 7.5° to the direction of travel. I was hoping in a dense fluid like water, 7.5° might add a knot or two ?