Hi i am trying to join friends on the ferry that departs from (Hong kong)Kowloon to Zhongshan

Is there many passenger ferry services in Kowloon ? or is there 1 main ferry service?

do you know what the website add is .I am hoping to purchase tickets online prior to travel....
Or is it easy ,guaranteed to be able to purchase tickets on the day...We are leaving 20/04/15.


Appreciate your response in this matter.