Although marabou and schlappen have similar action in the water, I don't think you tie them to a hook the same at all. Granted I'm a novice tier, but here is my experience so far.
Marabou you remove from the stem and tie. Schlappen you tie the stem to the hook, then spin or palmer it like you would a regular hackle. I trim off the thickest part of the stem, and then I only spin the bottom third of the feather before I tie it off and start a new one. The bottom part of the schlappen is bushy like marabou, the top part is not (more barbules ? )