Now, we have fitted the propeller. Propeller basically is a hydrodynamic device which pulls water from ahead and throws it back like an axial fan. The water flows fast the propeller impacts energy to the water. So, water flows at a higher velocity around the ship. Now, we have seen that the velocity of water is related to resistance of the ship. So, when the propeller is moving behind the ship due to change of velocity of water in the stern part, there will be a change in the force required to push the ship forward which will be higher. In other words, the thrust that the propeller would give would not be equal to the resistance of the ship, but will have to be higher than the resistance of the ship. Can you understand that?