I've never heard of these before! They work by sitting on 'ground effect', the cushion of air between the wing of a plane and the ground. Apparently over water, the ground effect is strong enough to hold up some real monsters!
The fact that they are a cold war era obsession of the Russians makes them even more delightful.
Comments
Ah the old caspian sea monster invented by the father of the modern hydrofoil Rostislav Alexeyev
there was a very good program about these a few years back
it was an episode of equinox in 1998 might be torrentable somewhere
http://ftvdb.bfi.org.uk/sift/title/600266