Probably like you, I am tired of birds using my boat as a restroom.
I have found what is turning out to be a terrific, easy and low-cost solution.
I purchased some bird chaser tape (bird scare flash tape) on the Internet and mounted a 3-foot piece to a boat hook, and placed the boat hook in a rod holder. I attached a piece of the tape to the hook with a spring clip. Small pieces break off in the wind so I replace it about every two weeks or so as it gets too short.
Amazing! As far as I can tell, I haven't had a single bird land on my boat (during daylight hours and when the sun is out). This stuff really works. It is incredibly shiny so I guess the noise and flashing scares them away. Made me put on my bell bottoms and Saturday Night Fever on my stereo.