In actual reality there would be wind and water currents diverting any ship sailing that route from the depicted “line” anyway so the whole argument is pointless
The only straight line paths in the universe are followed by electrostatically uncharged non-accelerating objects in free fall in a vacuum. Or massless particles.
Spacetime is curved. Inertial paths through spacetime are straight.
Euclidean space is not the only space where straight lines are possible.