A thruster has 3 fins whereas a twinzer has 2
Thats about as advanced as I can give
I'd sail like crap on either
my completely uneducated opinion is that with a thruster, the outer two fins are angled in towards the middle.
Gives you faster carves off the lip and quicker bottom turns, but slows down the straight line speed.
the new twinnies, seem to have the fins parallel to each other.
of course, I could be completely wrong, and usually am (just ask the missus
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Which one ..... Tri-fin or thruster?? 
A tri-fin should in theory be better than a twinnie... a happy medium between a single and a twinnie.
BUT if that is the case then why did starboard bring out a twin for 2009, when they were so obviously testing tri-fins for the last 18 months or so 
hmmmm
I"ve only got ancient surfboard experience, don't know how that translates to modern waveboards.
He comes my history ramble, so if you don't want to listen to an old fart's ramblings, move on now!
I modified my mal of the time to a twinny about 1967/68, at the time I hadn't heard of anybody else doing it, my reason was to try and stop spin out, (with wide back boards, on big bottom turns the fin could come too close to the water surface, losing traction), with out reducing maneuverability. Back then the solution to spin out was to use longer and longer fins, making the board harder to turn.
I thought by putting smaller fins close to the rails, at least one would be buried deep, sounds good in theory, but back then I didn't quite understand why boards turned. mounted the fins parallel to center line, (as you would) board wouldn't turn at all!! Unfortunately it just didn't occur to me to give them any toe in, or move them more inboard. Just thought the whole idea of twinnys was useless.
Over 10 years later, my eyes were opened to the benifits of "toe in" when the son of an American TV star, (Mat Dillon from "Gunsmoke") carved Bells on his twinny and I think won the Bells comp that year. Twinnys became very popular here after that, so loose, maneuverable, and no spin out.
But they had one draw back, you couldn't get any thrust out of the bottom turn.
The back just slides around following the inside fin's toe in, like doing a rear wheel drift in a car, nothing to push against.
That's when the thruster came into existence and took over, had almost as much maneuverability, and you could push out of a bottom turn and get a lot of acceleration.
So coming back to modern waveboards, ????????
hmmmm
Yeah I would believe such a thing.... considering some of the secret things I saw at undisclosed locations would suggest a very very good tri-fin was coming soon.
Alternatively: Maybe starboard were going to release a tri-fin or thruster and then they saw what Kauli was doing on a Quatro twinny ....... no point making the best thruster in the world and releasing it 6 months AFTER a pro was ripping up Cabo on a twinny and the whole world was talking about how good twins are
I postulate that Starboard's triple protos were much better than their twin protos..... but they are releasing the latter as it will make more cashola as a Quatro rider has already sold the concept on the public (baaa baaa baaa )
Discuss
i say bring on the quads.....
all the features of the twinny but with the performace of a thruster.
)
Yeah I saw hotshots rip on thrusters in 1995. Also saw Robby Naish sail a beginner's board in waves and backloop it better than me 
Anything with a good shape will be used to it's full potential by those who get to sail it daily, and they will make the rest of us look sh!te.
I'll stick with single fins.
)
i can't remember the exact explanation but it was a good one, i think it was something like this.
with surf boards. twins are really manouverable and fast but they aren't too stable, the thruster set up gives you that added stability and a little extra lift to help with the front rail.
On a windsurfer i think it's a thruster can provide great drive on a wave but you have to sail spot on, and they are a bit slow, also you have a sail and foot straps to help load the front rail.
twinz make it a it easier with the rail and turning but don't loose that much speed.
i think that's it
WAVE FINS ...... General guide
Fins deliver drive off the bottom ,carving grip off the top and increase your upwind abillity ................. but they gotta be, set up correctly ,angles to the nose,angles inwards,outwards, and then the deepth of the fins and the shape your using..... i.e....... full foil or curved inside foil.
Sounds complicated and it is ..............but specialised shapers have this information and knowledge gained through experimenting and riding different set ups.
Basically fins deliver the rider different drive and style options
1 Fin delivers to the rider One gear
2 Fins deliver to the rider two gear[
3 Fins you got 3 gears
4 Fins is 4 to da da floor.
Drag was always a factor with thrusters.........but it has NOW been converted to lift and early planning WITH OUT THE FEELING OF DRAG.
Trick ........ All 3 fins need to flex as one,,, on maxium drive.......... Thrusters should have a curved inside foil . Most efficient.
Different conbinations.........exist
Rough guide.....
M3 M5 SIDE FINS and a 210mm OR 220mm servern flex tip FOR approx.....85kg--110kg Punter riding a 80 Litres to 100 Litres of board.
110kg PLUS M7plus 220mm 230mm 100litres to 130 Litres
M3 M4 M5 200MM or 190MM 180mm 50KG ----85KG PUNTER riding a 50L TO 80Litre volume board.
You Want a board to start with that floats your weight and is balanced approx guide 1kg for every litre of volume to achive this ...........................................
so loose some weight you fat bastards.
That might of been directed at my self..........
