A boat tail, a tapering protrusion mounted on the rear of a lorry, can lead to fuel savings of up to 7.5%, according to road tests carried out by PART (Platform for Aerodynamic Road Transport), a Dutch public-private partnership.
The tail used in the trial was a tapering protrusion of about two metres in length mounted on the rear of a truck.
According to PART, the boat tail had already proved itself during wind-tunnel experiments and computer simulations, both conducted at TU Delft, in theory and using small-scale models.
Now an articulated lorry fitted with a boat tail has also undergone extensive testing on public highways.
The vehicle was driven for a year with a boat tail (of varying length) and for one year without the device. The optimum boat-tail length proved to be two metres.
PART’s mission is to reduce fuel consumption in the road-transport industry by improving aerodynamics. It wants to achieve a 20% reduction in fuel consumption and carbon-dioxide emissions in the European road-transport industry by 2020.
PART has previously conducted road tests on a new generation of aerodynamic side skirts, which were scheduled to make their commercial debut late-2009.
Today, several aerodynamic solutions are available for both the tractor and the trailer of artics, and with advanced engineering tools such as wind tunnels and computer simulations, the aerodynamic drag level of trucks can be improved even further.
Fuel-economy improvements of up to 10% are already achievable employing commonly used devices such as cab hoods, streamlined mirrors and tractor/trailer skirts.
The more drag is reduced, the greater the engine power available for moving a vehicle and its cargo.
However, the faster a heavy goods vehicle goes, the greater the energy penalty becomes. For example, at a constant speed of 50kph (30mph), less than 40% of the engine power is used to overcome drag, as against 60% at a speed of 80kph (50mph).
Crosswind, interference with other traffic and weather conditions all have an effect on the aerodynamic forces that ultimately need to be overcome – and these constantly changing factors increase drag.