Is it possible to restart a PhD due to issues with supervisor (and should I do it)? I am a PhD student in Europe and I am in the state of permanent crisis because of my PhD supervisor. He is a very nice person, who is very active with public engagement, very successful at grant applications and all that. But the problem is, it turns out he does not know the subject. Now I realize this is a very arrogant thing to say. However, for a very long time I refused to believe it and thought that there was some problem with me. Now all evidence (corroborated by others) shows that he really is incompetent. He somehow manages to pull it off, getting on other people's papers and so on.

The fact that this takes place in Europe is significant: I had to choose someone from the start of my PhD and the time is extremely limited. Also, I am not sure, but I have an impression that you will not be able to get funded, if you quit your PhD and start over. Is this so? Also, there is a very small number of people doing similar things around and none in the same institution. Additionally, it seems very likely, that no one would support a rebellion (i.e. switching a supervisor), because of politics.

I have a very good track record, I finished at a top American university with very high grades, and most importantly I do want to do research. So this situation makes me very unhappy. I can't see any way out, but maybe there is someone who can? I will consider changing the field somewhat (but not too radically) and starting over, but it seems like the funding will most definitely not be available. Or maybe it will?
Adding a student's perspective to Pete's answer:

My advisor told me at the being of my master thesis, that soon I would know more about my particular area of research than him. At the time I didn't believe a word he said, but at our third meeting I was already explaining stuff to him and by the fifth I started to feel irritated that I had to explain stuff to him which I didn't have to explain to his PhD student whom I collaborated with.

But then I realised that I worked on this topic all day every day, my collaborator worked on a related topic and discussed my research with me several times a week but my advisor only got to spend time on this topic every other week when we met with him, because he had plenty of other students to advise in the meantime and also had his own research, teaching and some administration to do.

So from the sixth meeting on it became a habit for me to open the meeting with a quick catch up on my topic and my progress before diving into the details. And from that meeting on I always got great advice from him.

I think you need to think about whether you have given your advisor a fair chance to help you when you were stuck and whether he has been able to help in that regard, because that's his job and knowing all the details about your current topic is your job.