I am another victim of to much time on my hands. To be fair, most I spend refereeing my kids. But when I get time, it's BT designing and forums or Diablo3.
Hovercraft Designing. So the smallest you can make a combat hovercraft is 2 tons (.5 ton engine, internal, control, lift) without going to fractional accounting. It will have no armor, and you have to use a light or xl/xxl fusion engine and go at least 21/31. (also helps if you base your math off of the master table ... 10 rated fusion engine is .5 tons +%50 vehicle mod = .75 tons x .5 or 1/3 will get you .375 or .25 rounding to .5 which is a nice %20 of 2).
IF, you use fractional accounting and get semi-creative you can get more on the vehicle, possible an infantry scale weapon or three.
Also with fractional accounting and creative sub-10 engine ratings we can get a ONE ton hovercraft!
(note: all purely academic with the possibility of failure, I don't foresee a legitimate application for this vehicle)
For the engine I went with the protomech rules. Not sure how else to justify an engine rating below 10 using combat vehicle rules (support veh engine rules give a 2.1 engine weight which won't help).
1 ton Hover, Tech Level F (?)
Engine: ER-1 .025 (protomech engine formula), rounds up to .2 for %20
Speed: 41/61
Cruise: 442.8 kph / 275 mph
Flank: 658.8 kph / 409.4 mph
Internal: .1 (1 pt)
Control: .05 (1 Crew)
Lift: .1
Armor: .25 (4 points: 1/1/1/1)
Equipment: .3 – Seating 4 (.075 each)
I can't imagine going over 400 mph on open ground. I'd just puke and have it spray all over me and anyone else.