The following video is an excellent explanation on how ships sink below the horizon. It is based on mirroring. The further a ship is over the horizon the higher the mirror-line gets. This certainly is suggesting a continuation of a plane and not a globe. The author of this video forgets to mention that from our point of view the line of sight actually cuts of the underside of the boat. The further the more it cuts of... Over this mirrored line of sight everything that is above that line of sight will be mirrored over that mirrored line of sight. This works as shown in the following impression.