Like squeezing a wet pumpkin seed, a sailboat goes to weather
when it can resist the sideways force of the wind
. So a keel
of some sort is required: without it, a hull can't go any closer to the wind
than the old Galleons could. It just blows sideways.
But that was good enough for the Conquistadores.
A junk rig has less healing force because it's center of pressure is not as high as a sloop
rig might be. That just says the middle of the sail is lower.
So: yes you can put any kind of sail you want on a 'cabin cruiser' and it will go down wind. Of course. it will go downwind without a sail, too. If the sail is bigger than a kite, it may make the boat flop all over the place, and the tiny rudders on a lot of power boats won't work very well, they were meant to operate in the high-speed flow of the propeller(s).
Add a keel
to resist sideways motion, more rudder
area to work in slow speed water
, and a mast
that can stand a lot of wind force, and you have a sailboat, but one that will fall over on its side because it doesn't have ballast or outriggers to keep it upright!
Okay, add a mast
, a heavy keel, a rudder
, some winches to deal with the really big loads, and you have...
A really ugly sailboat! And you've spent a ridiculous amount of time and money
to get one that doesn't sail worth a tinker's damn because the hull shape is wrong.
Morale: If you want a sailboat, buy or build one. If you have a 'cabin cruiser' and you want a sailboat, sell the cabin cruiser and buy or build a sailboat. If you like the look of a junk rig, get a junk rig. If you want to sail upwind better, buy a better sailing rig. There is a reason why motor-sailors look more like sailboats than motor
boats, and it has to do with suiting the design to deal with what Mother Nature provides for free rather than trying to beat Mother Nature into submission in a cloud of fumes! In the end, Mother Nature wins.