Is there a boat/ferry from Zhuhai to Guangzhou?

I'm afraid there is no ferry service between ZH and Guangzhou now. If your destination is Lianhuashan Port, you can take a bullet train at ZH Railway Station near Gongbei to Guangzhou South first. Then walk to the nearby South Bus Station to take bus Pan 100 to Xinghai Park, where transfer to bus Pan 92 Long Line to Shilou Police Station stop and then walk there. If your destination is other place in Guangzhou, you are advised to make full use of the metro system, bus and taxi to reach upon arriving at the South Station.

Beth gave you a good way, but if you really wish to travel by ferry, there is a method for you. At Jiuzhou Port of ZH, you can take a ferry to China Ferry Terminal in HK. There you can transfer to another ferry to Guangzhou Lianhuashan and the ferries are scheduled at 07:50, 09:00, 10:50, 14:00 and 18:20 . In this way, you may need to consider the visa matter I'm afraid.