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Regulations Now Permit Boat-tails But Should You Adopt Them?


On 14th February this year, the DfT changed legislation to allow for and encourage the use of safer and more environmentally-friendly HGVs on the UKs roads.  The key changes refer to the elongation of both tractor units and trailers with the view to improving aerodynamic performance, driver visibility and comfort, but should you be urgently calling your suppliers before you finish your coffee to retro-fit them to your fleet?  Don-Bur examines the new regulations and some of the pros and cons.

What exactly does this new regulation mean?  If we focus on the trailer aspects, the new regulation exempts vehicles using rear aerodynamic devices and equipment from the calculation of ‘overall length’ and ‘overall width’.  In simple terms, this means an operator can fit ‘devices or equipment that are designed to reduce the aerodynamic drag’ to the rear of a maximum length trailer; adding up to 500mm in length.  In addition, an allowance is made for an additional 25mm per side up to a maximum of 2.6m wide.

boat-tail open boat tail closed

There is no doubt that this aerodynamic evolution works.  A 2013 study estimated that 7-13% fuel savings could result and, from a trailer bias, Don-Bur agrees.  A fitted “TrailerTail” boat-tail, under operational trial for one of their clients on a standard curtainsider, recorded an impressive fuel saving of 7%.   At today’s bulk diesel price of 128.38ppl, an operator could save in the region of £3,394† and a 7-tonne reduction in CO2 output per annum.  As a result, payback periods are rapid and you get a significant positive mention in your end-of-year sustainability report.

So why hesitate?  As with many aerodynamic device add-ons, they can be susceptible to damage and, as much as we’d all like to fool ourselves, accidents have to be a built-in expectation when working out a business case.  Boat-tails, by their very nature, are located in the one area that tends to get the most abuse and all it would take is for one driver to accidentally reverse into a dock with a boat-tail deployed and you immediately negate any hard-earned savings to date.

You may think, with this in mind, that boat-tails would have been developed to minimise the risk of damage; perhaps manufactured using some clever deformable ABS plastic that always springs back into shape or indeed a design that retracted entirely into the bodywork, leaving nothing exposed or vulnerable.  In Don-Bur’s experience, this is not always the case.  The regulations state that boat-tail devices have to be ‘foldable’ or ‘retractable’ and many designs are constructed using lightweight GRP fins, held together by a series of pulleys, hinges and/or wires which are required to fold the system away.  This complexity increases risk and, at this point, you would be forgiven for questioning what every operator wants…. the value.

There are positive points here.  Boat-tails will save a considerable chunk of your diesel budget and they can (and should be) fitted in conditions where damage is less likely.  Side loading environments would make side skirts a difficult investment but a rear-mounted boat-tail? It would be wise to give this serious consideration; particularly if that curtainsider is a double deck where the significant drag at the rear is, literally, holding you back.

The future is looking promising too.  Work is already under way at Don-Bur and their selected partners to develop alternatives to existing designs; alternatives that will take the daily punishment and still perform well over the lifespan of the vehicle.

† Based on a trailer travelling 80,000 miles per year.  Bulk diesel price of 128.38ppl obtained from the RAC Foundation and accurate at time of publication.  Control vehicle estimated to travel at 9mpg.  Comparison trailer fitted with TrailerTail travelling at 9.63mpg.


Additional Resources

The Regulation Change in Detail

The Road Vehicles (Construction & Use) regulations 1986 as amended by SI 2022/59 now allows the fitment and use of elongated cabs and aerodynamic devices on heavy goods vehicles on roads in Great Britain.

This aligns with the existing Masses & Dimensions Regulation (EU) 1230/2012 as amended by SI 2020/1393 which already allows for vehicles with aerodynamic devices and elongated cabs to be type approved.  Without amendment, the previous UK domestic version of the “C&U” regulations would have prohibited such vehicles on the basis that they would have exceeded previous dimensional limits.


There is, as you might expect, guidance from the DfT that includes limits on when you should or shouldn’t deploy a boat-tail.  For instance, it is advisable that the boat-tail is retracted or folded away when operating in urban areas, when reversing or parking and when loading or unloading; all fairly common-sense pointers. 

The overall length of these vehicles will continue to be constrained by the relevant turning circle requirements (in both the deployed and in-use position, or in the fixed in-use position) and the load length limits.

Vehicles with rear aerodynamic devices and equipment still need to comply with the lighting requirements in the Road Vehicles Lighting Regulations 1989 as amended, in particular, regulation 21 covering ‘Projecting trailers and vehicles carrying overhanging or projecting loads or equipment’.

DfT Links

DfT Announcement 14 Feb 2022:

DfT Guidance 14th Feb 2022:

Published: Thu 12 May 2022

Updated: Thu 11 Apr 2024

Author: Richard Owens

Published by: Don-Bur

Don-Bur (Bodies & Trailers) Ltd

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