I have a 19 footer that I bought a couple of yrs ago and the bottom paint ends below the water line. Since its a 30 year old boat it appears that its always been that way. It's been moored in fresh water for the past 10 yrs and I clean the hull with muric acid and it comes out ok with effort. Starting next year we're docking it in salt water. Should I paint the bottom paint up to the water line? Is there a reason that the factory painted the bottom lower than the water line?