Few questions regarding cruise

Hi, I'm interested in taking cruise or raft from Guilin to Yangshuo and I have read that foreigners have to go to some other harbor which is located out of the city of Guilin, but here you write that I can go from downtown? Is it really hard to get tickets, do I have to book in advance or is it OK if i buy ticket on spot. I f I would like to travel by raft (I read that it's possible) where I could take it? As I understand it's pretty easy to go back to Guilin from Yangshuo.