Since the boat has just been sitting at the dock for 6 weeks, yucky slime has grown at the waterline.  I finally decided it was time to bite the bullet and go scrub it off...

Easy peasy.  The bottom paint we applied last fall is doing well - no barnacles at all, just soft slime-algae.  It brushed right off.  I was in the water just about an hour to scrub the entire waterline.  Looks good for now.  I guess I'll be doing this every 6 weeks now!