I now know several ways in which rope belts don't work, and none in which they do.
Last week and a half I've been trying to attach the turbine to the alternator in a way which is a) not going to slip, b) runs smooth and easy, and c) isn't going to chew holes in itself. There's several ways I've found which will satisfy any two of these, but none that'll do them all.
So I've pretty much given up on that, and have gone for what I should've just done from the start, and used a bike chain. Or at least, one and a half.
I didn't want to do this for the two reasons that it's a little more resource intensive than I'd like (but at this stage, screw it), and that the smallest sprocket I can use, the one off the derailleur, only gives a gearing ratio of 15:1 from the turbine's bike wheel rim, and I was under the impression I've been needing at least 25:1 to get the alternator up to speed and kicking in at a low enough wind speed.
However some actual research has revealed that most car alts come in around one thousand to fifteen hundred rpm, not the twenty four hundred I was led to believe.
So 15:1 is actually perfect and I can use the chain after all. It's definitely and by far a more robust solution.

So that's all in place in terms of the benchtop test rig, which tomorrow I'll get the vacuum cleaner motor back on (after it rather catastrophically failed on the first firing up and sent a length of rope at my fathers head with not inconsiderable speed, luckily he's got fairly snappy reflexes) and we can get the thing tested before strapping it all on the back of the car and doing some actual power output runs.

That'll have to wait a week tho, as I'm off to Nelson on Sunday to get the construction workshop prepped for the following Saturday. Then it's back here for a week or so, then down to Christchurch for similar, then flying out to Perth.
Busy busy.
As according to the universal constant I've got exactly half done of what I'd wanted to, but it's all good. Just glad to be getting anywhere at all, really.