I totally agree with Revo on this subject. I purchased a 2010 Oasis last May and initially had the same issues you described. It took a few trips, a few peddle adjustments and readjusting the way I was making the strokes to finally figure it out. Even now when I go out and start slapping the bottom with the fins, I readjust my foot position to get the stroke I am looking for. I found not bringing the fin all the way up gives you far better propulsion, hence more speed and less effort. Keep experimenting. You will find the right techniques to give you a wonderful result. This is an amazing drive system!

Roger