The mussels in I-Bay were exceptionally bad this year. I've seen numerous boat bottoms completely covered with an inch of them if they weren't bottom painted. I have an outboard so haven't had an issue, but I did find transducers, trim tabs, outboard motor bracket and three water intakes all loaded up. Several Muriatic acid sprays and power washes did the trick. Bottom paint helps but only on flat hull surfaces. Not outdrives it seems.