I bought a 1992 Thundercraft Express 240 I/O. The original built-in depth finder has no display, and the speedometer doesn't work. I am guessing the depth finder transducer is dirty. It has algae around it, and the little hole at the bottom of the out-drive has algae around it it as well. My boat is in a slip. I don't really want to take the boat out of the water for these 2 issues. What's the best way to clean them off if it is the problem?