An increase in propulsion efficiency can be derived by extending the outlet of the propeller tunnel with a horizontal panel over the rudders. This so-called Flow Extender Plate shifts the mixing point of different water velocities further behind the ship. The higher outflow velocity of the propeller that is obtained leads to more effective propulsion as higher thrust is delivered at the same level of engine power.

The gain in propulsion efficiency is about 15%, but strongly depends on the aft ship geometry and hydrodynamic conditions of the propeller. For that reason the dimensions and shape of the panel are to be determined by means of computational fluid dynamic analysis or model tests.