I've sailed from South America to Australia, crossing the pacific.

The flat earth theory doesn't make sense to me based on this experience. Here are my two main objections:

I. Nautical navigation
Judging from the top picture it would be impossible to travel from Panama to Brisbane setting a direct course. A sailor would constantly have to steer his boat towards starboard in order to avoid the ice wall.

Sailing from Galapagos to Australia me and my shipmate more or less kept the boat moving in a straight line for months. We relied on GPS-signals, compass, maps, but also the stars to keep a steady course.

If the world looked like the picture in this post we would have crashed directly into the ice wall before even reaching French Polynesia.

II. The horizon.
Sailing on the sea we could only see so far over the horizon, If we climbed the mast we could see further. Standing on top of a mountain in Nuku Hiva I could see far across the ocean, but I think I would have been able to see a lot further had the earth been flat.