I had a convex mirror on my boat but still had blind spots on both sides that compromised safety in the busy channel I frequent.  This mirror is actually 3 separate mirrors. Once you've adjusted the center mirror as you would the rear view mirror on a car you can then adjust the two side mirrors individually as they are mounted on their own ball sockets.  All of the adjustments are somewhat stiff but that's a good thing as the adjustments stay in place even when bouncing through some chop.