Okay, sailorboy1, no airline blindfolds for you!
A friend of ours who is an architect, placed (probably used 4200 or local equivalent) "L" shaped plastic rails above and below the portlight. Then he had fabricated some white, but translucent panels
shaped like the portlights
, and slid them in as needed. He extended the rails to where he just slides them back and forth, not removing them each time.
It avoids the "frilly" look in a no-nonsense boat. But if you prefer curtains, usually you need something top and bottom to keep them tidy, as they will obey gravity when the boat is heeled. Stick on cuphooks with dowels can work. Painted to match or finish the dowels bright, if you prefer, then slide the curtains open and pull 'em closed.
Or, self adhesive
velcro dots on the outermost edges, and fabric
of choice with the other gender velcro in its corners. You will need to stitch the velcro to the cloth.
Or, learn to wake up to the sun, and enjoy the extension of your day. Give yourself a treat on arising.