[Karen W. (OP)]

I  know very little of these and how they work. I have played with a couple toy ones but don't undersand!

[another_someone]

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.htm

http://www.dover-kent.co.uk/transport/hovercraft.htm

I 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.html

http://www.jameshovercraft.co.uk/hover/mainpages/gallery-srn6.htm

Essentially, 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).

[daveshorts]

Appartently the Russians built a larger one:
http://foxxaero.homestead.com/indrad_068.html

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.

[Karen W. (OP)]

The Zubr is really big. That is a very cool picture and information. Thanks dave!

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.htm

http://www.dover-kent.co.uk/transport/hovercraft.htm

I 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.html

http://www.jameshovercraft.co.uk/hover/mainpages/gallery-srn6.htm

Essentially, 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).

Thanks for all the information George!

[another_someone]

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.

I think the added complication is that a hovercraft also benefits from a ground effect (i.e. air is directed at the group, and then bounces back up to the hovercraft).  Helicopters can use this effect also when they are very close to the ground, which is why a helicopter has higher altitude limits within ground effect (e.g. when hovering above a mountain) than it does when it is hovering in free air, and well away from the ground.  Since a hovercraft is always near the ground, it always has the benefit of ground effect.

[Karen W. (OP)]

Hey George What do they use to power a hovercraft? Fuel wise that is? is it completely out of the question that they will ever be used for more private modes of transportation? Do you think that they are just way to pricey and maybe not as practical.. It would surely cut down on road maintenience don't ya think! Is it plausible that business traffic like semi's could be diverted to more vehicals such as those? LOL I don't know sometimes It just seems they could make use of a technology like this for more then military purposes etc.

[daveshorts]

It depends what kind of engine you put on them, a petrol engined hovercraft will be powered by petrol, a gas turbine (jet engine) powered hovercraft will use kerosene.

Hovercraft are not very fuel efficient compared to something with wheels on a road at the best of times, but they are also very very bad at going up hill, especially slowly, as they are essentially blowing themselves up hill. If one was sitting still on a steep slope it would need to be at full throttle all the time just to stop it sliding back down. If they are to work on water they also need a very large surface area, so a 30 tonne hovercraft would need to be much larger than a 30 tonne truck. So they are unlikely to be used on land in a big way any time soon.

Hovercraft are however quite efficient on the flat, and the flatter the ground the less air you tend to loose out the side, so the less you have to pump in. They are used for moving heavy things around warehouses and factories and even for moving buildings and very heavy loads a short distance.

[Karen W. (OP)]

Moving Whole buildings??? Wow! I think they sound very interesting and I had never thought about going uphill. sounds like my rider lawn mower, it doesn't like hills uness you go really fast and get a running start at the hill!