Your setup looks correct to me, you just need to add an expression. There are a couple you could try:
This will rotate the fins across the length of the spline irrespective of the number of evenly segment used. This could be useful if you need to adjust the number of fins but maintain the overall rotation.
This uses the current segment number and a multiplier to calculate the rotation. Notice that I've halved the overall rotation, this is because the counter seems to take into consideration the default segments, even if none are present.
I hope that helps.