No, I am talking about an orbital polisher, not a rotary sander. As I understand it, the drive unit in the orbital polisher uses two different mechanical actions to spin the buffing pad when polishing the applied wax. The orbital polisher's action causes the pad (or in my case since the pad is a POS in the cheap units, the microfiber cloth) to both rotate in a circle and at the same time the pad oscillates in an eccentric pattern inside this larger circular rotating pattern of the polisher. Unlike the old style rotary buffers which you definitely do not want to use on a boat, orbital polishers are much safer and won't instill swirls or burn-through gel coat simply because of the slower speed of the rotating action as well as the buffering-effect the oscillating action provides. If you step up to a more expensive orbital polisher (which I think is over kill) there is a clutch which stops the pad from rotating if too much pressure is applied while performing the polishing. With the dual actions, you basically pay for this clutch that the more expensive orbital polishers have. This clutch in the DA's and the more expensive orbital polishers make both safe to use because the clutch should stop the action when too much pressure is applied to the surface. Both the $20 orbital polisher as well as an expensive dual action polishers oscillate rather than rotate so it will be pretty difficult to eat through the gel coat with either machine - it's just with the higher power of a DA, I don't want to take the chance because remember - and here is the caveat - what is safe on a auto finish may or may not be as safe with a gel coat finish depending upon how careful you are. What if that clutch doesn't engage before the gel coat is damaged? I do not want to take that chance, that is why I use the cheaper orbital polisher. That is my concern. A DA is great for a car finish as well as a gel coat if you don't slip up and the clutch works as intended. Personally, I'd rather have the slower speed of the orbital polisher when working on my gel coat. I simply prefer the cheaper product because it does oscillate at a slower (but highly effective) speed and the $20 model does not need a clutch because it moves at such a slow speed no damage will be caused. The DA's with a clutch will stop you also, hopefully, before you have burned through the gel coat. Once you learn what that "tolerance" is when working on gel coat, you are fine with a DA. The over-riding consideration of both effective products is your personal risk aversity when considering the difference between the hard surface of a car versus a soft gel coat surface of a boat. For me, the $20 orbital polisher has served me well and the proof is in the appearance of my boat.