To close this off
I launched the 6.4m Pilothouse on a twin axle roller trailer at Newquay. 1.5hr after high water, from the slip in the harbour. Its not a big slip, which turns into beach pretty quickly. The sand is fine to drive on. The slip is cobbled and not particularly steep so your good for most sized Ribs, cars etc.
Didn't need to get the car wet, any later and I'd have no option but to. There was a hose to wash down after. Access was down a steep hill, exit would be back up this, which may pose a problem for smaller cars etc, especially if met with traffic.
Overall not too bad and a delightful place to be.
Peter @ Boatsandoutboards4sale