You guys are getting really deep with the sinking masts. One of the most basic principles of perspective is called the vanish point. Those disappearing or sinking masts magically reappear upon the surface with the help of a telescope... and if they can reappear on the surface with a telescope.....then what surface are they on?     

http://www.theflatearthsociety.org/tiki/tiki-index.php?page=Ships+appear+to+sink+as+they+recede+past+the+horizon