I can remember being told early in my paddling career, "NEVER, EVER use a back stroke of any kind. They will only slow you down." However, there are times when I need the power of the reverse sweep to change my direction - without slowing the speed of the boat. That's when it's great to have an effective pry. Done well, this most powerful turning stroke does little to slow the boat, changes direction quickly, and lets me get on to paddling forward in my chosen direction (rather than paddling faster in the wrong direction!).
Let's take a look at the pry on flatwater. You'll find you know this stroke and use this in other places on the river. It is the stroke used to initiate stern squirts. It is the first few inches of the reverse sweep. It is the rudder you use while surfing.
Sitting upright, twist until your chest if facing the side of your boat. Your paddle is parallel to the side of the boat and your hands frame your chest. The back elbow is bent and low, which keeps your blade angle effectively vertical in the water. This, combined with a front hand that is out over the water, maintains a streamlined blade position, one that can initiate a change in direction without slowing you down.
WITHOUT MOVING YOUR FRONT HAND, without bending that front elbow, push your hip away from the back blade. You'll find the length of this stroke is limited. That's ok. The powerful turning portion of the stroke is found in these first 8 or so inches. In physics-speak, you are applying force in a way that results in the boat purely spinning. You have done nothing to add or detract from the speed of the boat. If you don't pay attention though, and THE ELBOW BENDS AND PULLS THE FRONT HAND IN, the orientation of the blade changes to create a strong braking force. This is the traditional reverse sweep. The key to a gliding pry is knowing that less is more! Eight inches is enough!
This is the most powerful turning stroke because the chest is totally wound up in the direction of the desired turn prior to initiating the stroke. That's pure, potential energy waiting to be unleashed. As soon as the paddle anchors in the water, BAM! -those abdominal muscles, twisted like rubber bands, unwind, driving the boat with the legs into the turn!
It takes mental control to choose the best stroke for the job. Many paddlers in the crux of a move who realize they need to change their angle, unconsciously stick the blade in the water out from the hip in a flurry of activity. The thought is, "HURRY! HURRY!". With no pre-leading chest to give power to the stroke, it can take 2 or 3 of these inefficient turning strokes to get the boat to respond. While this frantic jabbing may change the direction of the boat, it also slows or stops the speed. This can lead to instability. By then, anxiety is high, the move is past, and often the boater is up-side-down!
With mental control, knowing that faster isn't faster, taking the time to choose the best stroke for the job, winding up fully in the direction of the turn, and using only that first 8 inches there is success! The boat turns while still gliding forward as you slice the blade from the pry into a forward stroke and continue toward your destination!