Whether the Earth is sphere, or flat and round, circumnavigation is not an issue here. Think of a needle going around on a record player.
“Circular sailing no more proves the world to be a globe than an equilateral triangle. The sailing round the world would, of course, take very much longer, but, in principle, it is exactly the same as that of the yachtsman circumnavigating the Isle of Wight. Let me give a simple illustration. A boy wants to sail his iron toy boat by a magnet, so he gets a basin, in the middle of which he places a soap-dish, or anything else which he may think suitable to represent the Earth, and then fills the basin with water to display the sea. He puts in his boat and draws it by the magnet round his little world. But the boat never passes over the rim to sail under the basin, as if that were globular, instead of being simply circular. So is it in this world of ours; from the extreme South we can sail from East to West or from West to East around it, but we cannot sail from North to South or from South to North, for we cannot break through intervening lands, nor pass the impenetrable ramparts of ice and rocks which enclose the great Southern Circumference.” -David Wardlaw Scott, “Terra Firma” (68)
“A very good illustration of the circum-navigation of a plane will be seen by taking a round table, and fixing a pin in the centre to represent the magnetic pole. To this central pin attach a string drawn out to any distance towards the edge of the table. This string may represent the meridian of Greenwich, extending due north and south. If now a pencil or other object is placed across, or at right angles to the string, at any distance between the centre and the circumference of the table, it will represent a vessel standing due east and west. Now move the pencil and the string together in either direction, and it will be seen that by keeping the vessel (or pencil), square to the string it must of necessity describe a circle round the magnetic centre and return to the starting point in the opposite direction to that in which it first sailed.” -Dr. Samuel Rowbotham, “Zetetic Astronomy, Earth Not a Globe!” (226)