Because of our relatively slow hull speed and the benefits gained from the Humbolt ocean current, an interesting situation developed. Let me explain. That theoretical speed over time is known as engine distance. In reality of course, you never actually go that theoretical distance because of external and environmental factors. The actual distance you go based on real world observations is known cleverly enough as observed distance.
Observed distance is almost always less than the theoretical engine distance.
This makes sense. Also, a ship s hull moving through the water has a resistance to it. Intuitively, we know that. That resistance is known as drag. A ship s total drag coefficient is the combined resistance of both the hull through the water and the superstructure through the air.