Not on the 40.3, but on a Catalina 42. Talks to lots of folks before, and my personal experience is you must have one. Some designer said the three go slows on modern boats are shallow keel, roller furling mast, a fixed prop. I used a Maxprop on two boats. It increased boat speed by 1/2 knot, and equally importantly, let the boat back straight. Can get all the info you need from www.pyachr.com. I just ordered a 42ds and you can bet one is going on it.