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The largest one that I am aware of used to be the SRN4, that used to cross the channel from Dover to Calais (we used to use it regularly, and we mourn its demise greatly - but for many years it was becoming apparent that Westland (which bought out BHC, the company that originally manufactured them), was no longer providing spare parts for them, so they were being run by cannibalising some of the craft to keep others going, until ultimately it was no longer possible to keep this up).http://hovercraft-museum.org/http://www.jameshovercraft.co.uk/hover/mainpages/gallery-srn4.htmhttp://www.dover-kent.co.uk/transport/hovercraft.htmI don't know if the smaller SRN6 that used to run to the Isle of Wight still runs, although I believe the SRN6 still is used by varius coast guards, and naval forces. The SRN6 cannot carry vehicles.http://www.hovercraft-museum.org/srn6-tech.htmlhttp://www.jameshovercraft.co.uk/hover/mainpages/gallery-srn6.htmEssentially, at a very crude level, there is a similarity between the hovercraft and a helicopter, in that both rely on pushing air down in order to lift them off the ground. As I said, this is a very crude similarity, because whereas the helicopter relies on the constant downward thrust of air to keep aloft, the hovercraft has a massive skirt around its underside that traps the air, and maintains the pressure of air within that skirt (even that is a simplification).The great thing about a hovercraft was that since it rides on a cushion of air, rather than actually being on land or water, it can ride over any terrain, so whereas most ships will travel across water, and then have to carefully place themselves alongside docks on the waters edge, the hovercraft skimmed over the water, and then skimmed as easily over the tarmac runway it would come off the water onto, and just park itself anywhere on that tarmac apron, and the cars could just spill out onto the tarmac - it made loading and unloading exceptionally fast. The travel times were also very fast (very comparable to the eurotunnel, but the loading and unloading times for the eurotunnel are far inferior, and that capital costs of the eurotunnel were horrendous, as is the amount of land they have required to use for the terminus and associated track).
Yes the big difference between a helicopter and a hovercraft is that a helecopter is being held up just by the thrust of it's rotor, where as a hovercraft is basically sitting on a big leaky lilo (it doesn't have a bottom, so it has to keep pumping more air into it.