Zipper - by William D. Jackson. Zipper rides like a pair of water skis except that you can maneuver like a star in a water thrill show by gently nudging the tiller bar with your feet. Your hands are free to operate the throttle and apply plenty of body-english to your turns. Speeds up to 36 mph are possible with 18-hp motors, but even a little 5-hp kicker will perform to please the most jaundiced boating fan.