Tests conducted in Europe have shown that a boat tail – a tapering protrusion mounted on the rear of a truck – leads to fuel savings of 7.5 percent. The fuel savings, which also means a cut in emissions, were realized by the boat tail dramatically reducing the drag caused by the lower-pressure effect that occurs in the wake of a vehicle.

The boat tail had already proved itself during wind tunnel experiments and computer simulations, in theory and using small-scale models. Now an articulated lorry fitted with a boat tail has also undergone extensive testing on public highways and borne the theory out. The lorry was driven for a period of one year with a boat tail of varying lengths and one year without a boat tail. The improved aerodynamics were dependent on the length of the boat tail, with the optimum length found to be two meters (6.5-feet).

Boat tail reduces truck fuel consumption by 7.5 percent [Gizmag]