I am struggling a bit in trying to verbalize the technique used when doing stern rudders. If you were explaining to a new paddler how to do an inside turn vs. an outside turn using the stern rudder, how do you explain the paddle position for each?
Understand and show. Visual cues convey skills much more than verbalizing them only.
Trouble understanding how to to them
or just trouble explaining how to do them?
The article referenced above is pretty good, I thought. I think front surfing on waves is one of the best ways to learn the stern pry/stern draw combo but a lot of beginners don't have the boat control to get on to a wave or stay on it long enough to try them.
If you can find a low bridge (without much traffic) or a safe place in the river in which you can stand with some nice, even current just downstream, you can attach a short tow rope onto the bow grab loop of a student's boat so that you can fix them in the current and watch as they try to angle the bow one way and the other using stern pries and stern draws. This also allows the beginner to look at their trailing paddle blade to watch the mechanics of the stroke and make sure that the blade stays close to the boat. Watching the blade (when first learning) also helps promote the proper torso rotation.
When used in this way (i.e, surfing) the strokes are largely static strokes relying on the force of the flowing water on the paddle blade to affect the turn. To switch from the stern pry to the stern draw requires little or no change in body or paddle blade position. In the stern pry the skyward edge of the immersed blade is angled slightly in toward the hull of the boat and the torso muscles coupled to the paddle shaft through the arms exerts a bit of inward force on the blade towards the hull so that the power face is loaded.
To go to the stern pry requires rolling the wrists down a little so that the skyward edge of the immersed blade is angled slightly away from the boat and the torso exerts a little outward force on the blade so that the back face of the blade is loaded.
To get into the proper position to do either stroke requires a good bit of torso rotation with the forward hand well out over the water. When the torso is rotated that much to begin with, it is hard for most folks to get a lot of force on the power face to rotate even more, so the stern draw is typically much weaker than the stern pry. The problem with the stern pry is that most beginners allow the blade to stray too far out from the boat, creating too much drag and killing their momentum or dragging them selves off the wave. It is usually better to take the paddle blade out of the water and reinsert it close to the hull if the blade has strayed more than 6" from the boat and you still need more pry.
Of course, there are times when you might want to introduce some drag intentionally, as the article suggests, to back yourself up onto a wave face or the foam pile of a wave/hole to unpin your bow. Another example would be if you want to kill your forward momentum and make a snap 180 degree turn, in which the stern pry can be brought forward as a reverse sweeping low brace, coupled with a pronounced boat heel.
Are you wanting to explain to someone how to make turns without killing forward momentum utilizing either the stern pry or stern draw? If I wanted to use a stern pry to execute a turn toward my paddle side I would simply continue a forward stroke well back to the position described in the article until the trailing blade virtually touches the hull, then execute a quick 4-6" outward pry before quickly going to a forward stroke on the opposite side (coupled with the appropriate boat heel).
To turn away from the paddle side using the stern draw I would simply heel the boat and use a forward sweep with emphasis on the last 6" of the forward sweep. The active stern draw is really just the last bit of the forward sweep anyway. When doing this I have seen quite a few beginners trip over their paddle blade, especially if they are using a heel towards the off-side of the turn (in this case, the side the draw is executed on). The stern skids out, hits the paddle abruptly, and the boat rolls over. I think that is something that just has to happen to someone a few times before they get the feel for when to end the stroke.
I have known experienced whitewater kayakers who don't really know the stern pry. The reason is obvious. As a kayaker you have the advantage of a second blade. When you are surfing a wave and need to angle the bow back toward your paddle side, it is often as quick and easier to simply take a forward stroke on the opposite side, which will also pull yourself back onto the wave trough if you are slipping back off. Whitewater open boaters don't have that luxury and have to depend on either cross forward strokes or a good stern pry.
A few videos on youtube
which may or may not be helpful to those teaching the stern rudder to others:
The first two videos emphasize and demonstrate combining stern rudders with boat edging. The last video shows the stern rudder being used without much boat heel and also demonstrates (in a somewhat exaggerated fashion) the “wrist rolling” involved in going from the stern pry to the stern draw.
I don’t agree with a statement made in the second video which in effect claims that the stern pry is one of the first turning strokes that beginners learn instinctively but that it is not very efficient. What I have seen beginning boaters (both canoeists and kayakers) use instinctively is a reverse sweep in which the paddle blade starts out too far from the hull (as a result of not enough torso rotation) and sweeps out to 90 degrees from the keel line of the boat.
IMO the stern pry, if done properly, is about the strongest stroke that can be used to yaw the bow to the paddle side for both a canoe or kayak. In a kayak, however, it is often even more efficient to simply switch over to a forward stroke on the opposite side, adding a bit of sweep component if necessary, especially if one wants to maintain forward momentum or move back up onto the trough of a surf wave. The first video sort of demonstrates this.
I am guessing the OP
wants to do/teach a proper stern draw/pry with a sea kayak.
Its one of the essentials of handling a kayak in waves and not confined to river use.