You posted....
Well at the risk of being modded:
JP seems to suggest 50N/m2 is the same as 33lbf/ft2. By inspection it is not. 50N/m2 is in fact 1.04lbf/ft2. Best not to use pounds as one may be confused by pounds mass, pounds force and poundals.
If you know the force in Newtons required to move your yacht you may then work out the sail area required if a force of 50N/m2 is applied to the sails (in simple terms that is). If however you apply a force of 50N over and area of 1 m2 of the stern it will not move unless the required force to move it is 5.05 kgf which by inspection seems unlikely.
Sails are similar to curtains...you wouldn't need much sail...the genoa alone would be fine...to get underway in a light to moderate breeze...
I did indeed and you posted:
50 newtons is a reasonable force...
I said (roughly) 50 Newtons is a piddling little force.
You said it (50 Newtons) could move a 40ft yacht.....it can't.
However you and JP then drifted off into pressure (force per unit area) which is summat different.
Let's close this off.
50 Newtons can move a mass of 50kg at 1m/s
2 (it does become a bit more complicated in applied mechanics but I can't be arsed at this time of eve and it is well off topic)
50 N/m
2 will give a resultant force which is the product of the force and area it is applied over.
1 N/m
2 = 1 Pascal (unit of Pressure) which is so piddlingly small the usual unit is kPa which is till pretty small.
So back to the curtains! What is their mass?