The earliest ferries I remember were "Cowes Castle" and "Noris Castle", and the high speed service was then run by hydrofoils - Shearwater 3 thru to Shearwarer 6.
I believe all three ferries - Coews Castle, Noris Castle & Netley Castle were all sold to a Croation company.
You can fine loads of images of them (and others) here: http://www.simplonpc.co.uk/RedFunnel.html (http://www.simplonpc.co.uk/RedFunnel.html)