RE: water pump
Let me try to pull up a picture I labled for you, if I find it I will edit this post to include it.
The pump works by tapping into either the carb's iso block or to the crankcase, it draws water from your water pickup pushes it to your cooling head at idle but when you get moving the flow of the water overides the pulse action and flows freely thru the entire system. I guess I should have asked you for information about your boat, pictures would also help.