Hovercraft - what happened to them?

[rickshaw]

[PR19_Kit]

He's preaching to the converted in my case, I loved travelling on them and think they've been badly treated by many.

[frank2056]

I think the fact that eels were attracted to them caused their demise...

[PR19_Kit]

Eels? 

[frank2056]

[steelpillow]

Tear off the skirt, fit wings and call it an Ekranoplan?

[Weaver]

"You are hereby charged with publishing an English to Hungarian phrasebook, with intent to cause a breach of the peace."

[Captain Canada]

So cool. The Canadian Coast Guard uses a few Hovercraft. Griffon Hoverworks is now designing some new ones for them as well.

[Nick]

The wonderful RNLI use hovercraft for rescues in shallow areas with mudflats and quicksand. Morecambe Bay is one, also Southend and Hunstanton on the east coast.

https://rnli.org/what-we-do/lifeboats-and-stations/our-lifeboat-fleet/rescue-hovercraft

[Andrew Gorman]

There are some still in use on the North Slope in Alaska.  Very handy to be able to travel over water, ice, and broken ice.
https://info.lynden.com/blog/hovercraft-teams-provide-essential-services-in-alaska

[Weaver]

The answer to the question is really: "they found their niche".

Unfortunately for them, it's not as big a niche as proponents of them were claiming in the 1960s and 1970s. Hovercraft running costs and maintenance schedule are closer to those of an aircraft than those of a normal ship and they're more affected by bad weather too, so if a ship can do the job it's usually cheaper to use one, even if it's a bit slower and has to sail a bit further to reach a proper port. Commercial operations tend to be more cost-sensitve than time-sensitive. Most of the litoral sea/swamp/ice regions where hovercraft show an advantage in flexibility don't generate enough economic activity to pay for them.

The military has really only found them useful for amphibious landings and patrol. They're too weather-sensitive to use as open-ocean patrol/fast attack craft. Some experienced military designers believed (and still do) that hovercraft could be useful for minesweeping work, but the high operating costs have put most navies off: it's the equivalent of running the US Navy's MH-53E Sea Dragon helicopters.

That just leaves civilian rescue, where again, running costs and weather sensitivity mean that a lifeboat or coastguard cutter is more use in most situations. It's only in oddball local conditions like Morecambe Bay that hovercraft show an advantage.

Hovercraft can travel on land in principle, but they're very bad at climbing gradients or stopping suddenly, and they don't work at all on broken ground that causes air to leak out from their skirts. Those same skirts are very big relative to the weight of the craft, which means they don't mix well with other traffic, and they also blow up prodigious amounts of dust or sand when used on those surfaces. Again, there's no compelling reason to use them that outweighs their disadvantages.

Another issue with all hovercraft niches is that in many cases they tend to get smaller, or even disappear, over time, due to what you might call "gentrification of habitat". That is to say, if you have an area that's economically viable to cross, at hovercraft prices, where cheaper vehicles can't operate, and that situation goes on for long enough, then sooner or later someone will build roads across that area so that you CAN use cheaper vehicles, and then the hovercraft will be out of a job. It's a situation somewhat analogous to that of civil STOL aircraft: runways only ever get longer over time, not shorter, to the point where you don't need STOL any more.

[PR19_Kit]

As with many technologies, the negative, and positive, aspects of the stuff don't really show up until some practical examples have been built, tested and tried in service.

[Weaver]

As with many technologies, the negative, and positive, aspects of the stuff don't really show up until some practical examples have been built, tested and tried in service.

Indeed, and as with many technologies, in the early days you'll get staunch traditionalists claiming that it's absolutely useless and ardent converts claiming that it's going to change the world. The truth is usually (but not always) somewhere in-between.   The question is where...

[steelpillow]

I still think that racing hovercraft round a track with banked corners would be fun. Brooklands, Monza, Sitges-Terramar, Indianapolis - a fine racing season.

Talk about not grounding the suspension!

[Weaver]

I still think that racing hovercraft round a track with banked corners would be fun. Brooklands, Monza, Sitges-Terramar, Indianapolis - a fine racing season.

Talk about not grounding the suspension!

That needs some head-scratching to figure out.

The point of banking with wheeled vehicles is to redirect some of the cornering forces down through the tires to increase grip, thereby countering the rest of the cornering forces that are trying to push the vehicle sideways to the outside edge of the track. However a hovercraft has zero "grip", so generating downforce does nothing, except make the left fan work harder and/or reduce the ride height. I guess you could say that the tendency of a hovercraft to fall down the slope towards the middle of the turn under gravity counteracts the cornering force trying to push it up the slope towards the outside? The maths is above my pay grade, so I don't know what that does to the neccessary geometry of the track, but I'll bet a small amount of money that it'd need to be different from a standard car racing track.

Then again, would you even need to do that? When you watch hovercraft racing, the craft turn sideways towards the exit of the turn well before they get there but continue with their original velocity vector until their original momentum bleeding off is replace by their new momentum in the new direction, in other words they turn in a huge "skid" more like a speedway bike than a racing car (but don't push the analogy too far). Ironically, this means that higher power:weight ratio allows the hovercraft to make tighter turns, since it can accelerate in a new direction faster.