In smooth waves coming from the side, rudder down should not affect you negatively in the general case. It certainly should not cause you to roll over - the contrary, a nice rudder in the water increases stability as it slows down the rolling motion.
Where a rudder might cause you to go over is if you are being pushed from the side by a foam pile - the rudder might dig in the green water and flip you sideways. Edging will not help much if the rudder is still in the water.
Front-surfing with a rudder is easier if the rudder is in the water, as long as you keep straight enough and don't let the bow burry too deep. If the bow locks-in deep and causes you to beginto broach sideways to the wave, the rudder will not have enough power to slide the stern around to correct - in such casese youmight be better off without a rudder as you might beable to slide the stern with "stern rudder" paddle strokes more effectively.
You can still edge and stern rudder along with the kayak's rudder, as long as you are not fighting the kayak's rudder with your edging and stroke efforts - the rudder will just help your efforts be more effective or eliminate the need for wasting your efforts on steering altogether -;)
Rudders will make your kayak more affected by moving water, but again, once you get used to how they do get affected, you can use them to steer your kayak more effectively thanwithout them (as long, again, as you stay within the effective zone of the rudder and you are not fighting it).
Touring Kayak Paddles
Bent Shaft Canoe Paddles
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