Getting back to the original question in the post:
The type 212 has a 1.7 MW Siemens electric motor. This is what's going to be driving your prop.
If we make the reasonable assumption that flank speed on a 212 will take pretty close to the max output of this electric motor, for our purposes, let's say 1.5 MW, then we need to provide that power somehow.
The first way would be with batteries. Well there's very little info on how much battery power the 212 has, so we can't say much about how long a charged battery would last at flank speed.
We do know, however, that the fuel cells can directly drive the motor, so let's look at that.
Most type 212s have 2 Siemens PEM fuel cells rated for 120 kW each, so we have roughly 240 kW to work with. Already we can see a problem here! We need 1.5 MW of power to go flank speed, but we only have 0.240 MW of electricity available, so AIP does nothing for our sprint endurance.
Ultimately, the amount of time you can sprint will depend on how much juice your batteries can store. In order to charge your batteries, your power consumption has to be less than 0.240 MW, so you have to be going slow. In fact, if you just do the math, 240/1500 = 0.1666, so if power and speed scaled linearly, you wouldn't even be able to do all ahead 1/3rd using AIP direct! Luckily though, things are much more efficient at lower speeds, so you could probably get a decent amount on AIP only, but definitely not up to sprinting speeds. So AIP will let you do stuff for a long time at slow speeds, but it doesn't help if you need to go really fast.
Which brings us back to square one. What's the sprint endurance of a type 212? Without knowing what kind of batteries it has, who knows?
