b/ no, they are not connected
c/ I see a torque, but it's not possible in fact, because we don't give energy to the system but we can recover energy. I thought about the weight but the thread can be with weight near 0 N because we use pressure of water (it depend of altitude) not the weight of water.
Note: the space between square thread and grey thread is for example at 1Ám but the surface is equal at the up (or down) surface so the torque is high on the up surface (or down). Sure the anlge phase is not very important torque but it seems to exist. I don't find where's the problem ?