On the beached ship, Screwy paints a water/sky landscape on a placard to simulate the ship rocking by tipping the picture back and forth outside the porthole in order to make Meathead seasick. Watching Screwy, it is seen that he sometimes lifts the bottom of the painted placard above the bottom of the porthole window. However, when seen from inside the ship (where Meathead is), the view of the "water" (painted bottom of the placard) is unbroken.
When Screwy places the drawing of the sea that he painted on the ground, it is upside down in comparison to how he would hold it up to the porthole.