That the one from Weymouth? Condor? I used that and was good. All depends on the weather.
The most bouncy trip I had was when my mum and I dropped my Aunty off at Dover to a ferry where her son would meet her at the other end. Whilst at the port, saw tickets for a round trip over the channel on the Hovercraft (didn't get off in France, just turned around and got your Duty Free allowance. Good value for a Fiver
Those Hovercrafts were choppy old things and way more than the Fast Ferries. Shame they stopped the service but not sure if I would have been happy taking a car on one?