Trailer Towing

All operation of a motor vehicle with/without a trailer on the highway is covered by legislation. The principal legislation referred to here will be THE ROAD VEHICLES (CONSTRUCTION AND USE) REGULATIONS 2003 and is coded S.1. No 5 of 2003 (ROI) or Motor Vehicles (Construction and Use) Regulations (NI) and the Road Vehicles Lighting Regulations (NI) (CUR & RVLR).

The driver is the person immediately responsible. Should the offence happen with a club owned trailer or tow vehicle, then the club could also be charged; usually in the person of the club secretary.


Hitching Up

Do not give yourself a hernia by lifting the trailer nose up and aiming it on to the tow ball. Raise the coupling above the tow ball by winding the jockey wheel down. Persuade some trusting individual to stand by the trailer coupling and hold his/her hand above the coupling at a height that is visible through the rear window and reverse slowly to get the tow ball close to the coupling. Swing the trailer front to align the two parts and wind the jockey wheel up to engage and lock. It is good practice to wind the jockey wheel down to lift the rear of the car up a little to check that the coupling is fully engaged and locked. Now wind the jockey wheel fully up and reclamp the unit as far up as possible. Attach the breakaway chain or cable to the tow bracket or to the hook (if fitted), but not round the tow ball neck – this is not a secure fixing. If the coupling is of the old type with a hand-operated reversing catch, make sure this is not engaged before you drive off. Modern couplings are automatic.


It is assumed that all boat trailers will be braked; should this not be the case consult the Construction and Use Regs. The maximum permitted weight of a trailer with overrrun brakes is 3500 kg. This is the maximum permitted legal loaded weight, i.e. trailer and load of boats . However on a single axle trailer the likely limit on maximum weight will be set by the load carrying capacity of the tyres (see the section on tyres). The relationship between the weight of the trailer and the towing vehicle is usually quoted as a percentage. The weight of the towing vehicle (referred to as kerb side weight) can be found from a) vehicle handbook, b) vehicle technical manual or information or c) on some vehicles (particularly of continental manufacture) the vehicle information plate (usually found in the engine compartment). To find the gross trailer weight, add the weight of the unladen trailer (should be shown on the trailer information plate, together with the maximum laden weight) and the individual weights of the boat sections, oars and riggers. Alternatively take the laden trailer to a public weighbridge. To establish the individual weight of boat sections use a set of scales, e.g. bathroom scales, to weigh the boat sections (mark the weight for future reference on to the section, use paint such as a car touch-up pencil or brush, or small stick-on lettering protected by spray varnish). If you doubt the accuracy of the scales check them by using some of the weights from your weight training area. For guidance, the FISA minimum boat weights are: Boat type Weight (kg) 8+ 93 4x 52 4+ 51 4– 50 2+ 32 2– 27 2x 26 1x 14 Expect club boats to be slightly heavier e.g. 4+ @ 55 kg and 8+ @ 100 kg. The loaded trailer should be nose heavy i.e. it should exert a downward force on the tow ball of the towing vehicle of 50–75 kg. The exact recommended weight for your vehicle can be obtained from your handbook, the manufacturer’s information or the Caravan Club publish a data list which includes ‘nose weight’. To check the actual trailer nose weight, use the bathroom scales (protected by a piece of wood, unless you like greasy feet) under the trailer coupling. Alternatively use a proprietary nose weight indicator obtainable from a caravan dealer. Some boat trailers have the recommended nose weight shown on the plate. If you are not very experienced, use a trailer/tow vehicle weight ratio of around 85%. It is possible to go to 100% with experience and care. If using a specialised tow vehicle e.g. Land Rover or goods type vehicle, it is possible to tow a trailer in excess of the tow vehicle weight. However the manufacturer’s recommendations should be observed and care taken not to create a danger. Some examples of vehicle manufacturer recommendations are given below: Weight Kerb Tow Ford Mondeo 1.6LX 1044 kg 1100 kg Land Rover 1746 kg 4000 kg

The ‘Tow ‘ Weight’ figures as shown above are taken from the manufacturer’s figures and these refer to two passengers. If you carry more than this then deduct the extra ‘in car’ load from the recommended ‘Tow Weight’. When loading the trailer do remember to put the heavy sections on the lower tiers and the lighter sections on the upper tiers, e.g. sculling boats. This will help keep the centre of gravity lower and improve the stability; most trailer accidents involve overturning. The most common cause of poor stability is incorrect loading. Caravan magazines such as ‘Practical Caravan’ publish regular features on towcar choice, listing kerb weight, 85% weight, towing factor and a ready reckoner to assist in the choice.

Towing Speed

Keeping within speed limits. Do remember – a trailer may NOT be towed in the outer (overtaking lane) of a three or four lane motorway, (and in NI unless other lanes are closed). If you overtake a slower moving truck, you may notice that the driver flashes his headlights when you are safely in front. This is to indicate that you are clear to return to the inner lane. The polite response is to flash your tail lights.


Modern remould tyres carry speed rating symbols as per new tyres. Tyre construction can be either radial or cross-ply BUT must not be mixed on the same axle.

Tyre pressures – See below for some examples for trailer. Check with your vehicle handbook or if no information available increase by 0.3–0.4 bar (4–6 psi). Always check pressures cold. The same legislation applies to trailer tyres as to car tyres. If you have any doubts, ask your local tyre dealer to check them. If the tyres are not street legal then remember each tyre is a separate offence. Example, a tyre marked ‘155 R 13 81S’ – Maximum load 462 kg at 2.5 bar (36 psi), this would limit a single axle trailer to a maximum all-up weight of 924 kg (2033 lb). A conventional car type tyre has a 4 ply rating, a ‘reinforced’ tyre would have a greater pressure and load capacity. A ‘155 R 13’ reinforced would have an axle rating of 1045 kg (2303 lb) at a pressure of 2.9 bar (42 psi). A ‘195 R 14 PR6’ (Transit type) would have an axle rating of 1785 kg (3937 lb?) at a pressure of 3.75 bar (54 psi). A way of increasing the load carrying capacity is to use a twin axle close-coupled layout, thus the total load capacity is four times that of a single tyre. If you are unsure of the correct pressure ask your local tyre dealer. It is good practice to mark the tyre pressures on the wheel arch above the tyre, then anyone who uses the trailer can easily find the required pressures. Use contrasting car paint touch-up stick or small stick-on lettering protected with spray varnish.

Tow Vehicle Rear Suspension

Excessive deflection can affect towing stability and create problems such as headlamp alignment. This deflection can be caused by
1) low rear spring rate,
2) overloading of the towing vehicle,
3) excessive nose weight of trailer or
4) large vehicle tail overhang (the distance between the rear axle and the tow ball).

There are a number of proprietary rear spring stiffening aids on the market where excessive rear deflection is caused by (1) or (4). For (2) and (3) take the necessary steps to prevent the problem.


A good stabiliser can make a car/trailer combination much more stable and easier to handle on the road. Caravan centres will stock and advise on the latest types of stabiliser. However if the combination has poor stability then a stabiliser will only mask the problem which can re-emerge at higher speed.

Rear View Mirrors

Motor vehicles have one internal and one external offside mirror. If the internal mirror is blocked then it should have external mirrors offside and nearside. A boat trailer is more open than a caravan and the standard car interior rear-view mirror will often give a reasonable rear view. However it is recommended that extended caravan tow mirrors be used where necessary to obtain a view down the side of the trailer and obviate blind spots. Remember the mirror should not be more than 200 mm wider than the trailer , and when the tow vehicle is driven solo the extra mirrors should be removed or folded back.

Brakes (C&U refers to NI Regulations CUR)

Reg 18 C&U states that “Every part of every braking system and of means of operation thereof fitted to a vehicle shall be maintained in good and efficient working order and be properly adjusted”. Secondary Main or parking Efficiency–Minimum required for MOT test 50% 25% If a vehicle only reaches the above minimum, there is probably a fault. The parking brake should be capable of holding the combination on a gradient of at least 18% (1 in 8.33). Do remember to disengage the reversing catch (brake disabling lever) in normal use and to use the breakaway chain or cable. Most modern tow hitches have an automatic reversing catch. The breakaway chain is attached between the tow vehicle and the trailer handbrake and, in the event of the trailer becoming disconnected on the road, the chain applies the trailer handbrake. If the trailer is left on the roadway disconnected from the tow vehicle, it requires the handbrake applied or at least one wheel chocked or prevented from rotation (Reg 89 C&U).

Power to Weight Ratio

There are no hard and fast rules covering this. As a guide, a 1.5 litre petrol engine should be capable of towing a trailer of 85% of the tow vehicle weight, and above 1.5 litres should be capable of 100%. In general diesel engines have a lower power output than an equivalent size petrol engine.


When the trailer is coupled check the correct operation of the lights; remember that all lights “must be clean and in good working order”

Forward and Rearward Projection

A load on a vehicle which is not drawing a trailer, or on a Trailer of a combination of vehicles shall not project 3 metres To the rear beyond the rearmost point of the vehicle or Trailer (3.05m in NI). Where a load projects more than 1metre to the rear Beyond the rearmost point of the vehicle or trailer a warning Device shall be carried at the rear of he load during the day Time. A warning device means either a red flag or cloth At least 300 millimetres square. For towing in Great Britian check ARA web site. The law relating to the transportation of abnormal loads is complex. There is an exemption in GB law that applies only to oar propelled racing boats that removes some of the requirements that apply to abnormal loads in general. For towing in Great Britain check This is often relied upon as good practice elsewhere.


The trailer needs to be maintained in the same way as any motor vehicle, probably more so since they will often be stored out of doors in all weather for most of the year. Wheel bearings, brakes, tyres and lights need checking particularly at the start of the summer regatta season, to ensure that the trailer is street legal. It is uncommon that the tyres will wear out quickly due to road use, the more likely cause of deterioration is the exposure to ultra violet light. This causes surface cracking of the rubber. Good caravan practice is to store the wheels in the garage when not in use for a prolonged period.


It is (or should be) the collective responsibility of the individual crew who load their boat on to the trailer to ensure that it is correctly loaded and secured. The driver should then check the loading of the trailer before he/she sets off. When you first set off on a journey it is good practice to stop after a mile or two and check the security of the load; it is surprising how the various ties and fastenings loosen off with the vibration of the journey. Once the adjustments are made that usually solves the problem, but you will see truck drivers always rechecking their loads before starting the next leg of the journey. If the professionals do it, why not you? Be considerate to other road users. When towing, everything takes longer, allow more time for accelerating, overtaking and braking, make more use of the mirror. Read the road ahead and behind, look out for the effects of side winds from overtaking vehicles (a large vehicle will first push the combination to the left and then, as it gets about halfway past, will suck it to the right), cross winds from bridges etc. on exposed roads particularly on motorways. Do not let the speed build up going down hills, this will help to reduce the possibility of snaking. If the combination does snake, ease off, try not to brake, slow down gently. If you have to brake, do so gently, do not accelerate. Road hazards such as roundabouts should be taken at a lower speed than when solo – remember that the centre of gravity of the trailer will be higher above the ground than a conventional car and this means it is less stable and more liable to overturning if you treat a roundabout as a Grand Prix chicane. Ensure that all braking is done in a straight line, i.e. do not go into a corner and then brake; estimate the required speed and complete your braking before the actual corner. Going round corners, roundabouts, etc., keep in mind the much greater length of the combination and allow a greater turning circle, since the trailer will tend to follow a tighter curve than the tow vehicle. Practise smooth safe driving. For example, if you decide to overtake and swing out as you might when driving solo then there is every possibility of a degree of swing appearing. You must take the move slower and ease the vehicle out as opposed to swinging it out. 400 mm. Vertical distance to suit lateral placement and to form a matched pair.

Trailer Towing : Definitions

  • Kerbside weight – Weight of vehicle with full tank of petrol but no passengers or luggage. Can be found in your driver’s handbook or from the vehicle information plate.
  • Tow weight – The gross weight of a braked trailer, i.e. trailer and boat.
  • Gross train weight – Total weight of laden vehicle and trailer.
  • Gross vehicle weight – Maximum total weight of laden vehicle.

Towing the Line Safely 

The standard B category licence allow drivers to drive category ‘B’ vehicles (vehicles lessthan 3500 kg and a maximum of eight passenger seats), plus a braked trailer (no mention of braked in NI) up to 750 kg. These weights are total all-up weights, i.e. vehicle (or trailer) plus load. Thus a category ‘B’ driver can drive a combination of 3500 kg vehicle plus a 750 kg trailer – a combination of 4.25 tonnes. A heavier trailer may be towed provided the maximum combination is within the 4.25 tonne limit (3.5 tonne in NI) and the laden weight of the trailer is not greater than the unladen weight of the tow vehicle. (See towing entitlement- NI)  The laden weight of the trailer is that shown on the trailer ‘plate’ (it may be labelled as GVW) and this applies whether or not any load is actually carried. If there is a requirement to drive a vehicle/trailer combination where the tow vehicle is less than 3500 kg and the total vehicle/trailer combined weight exceeds 4.25 tonnes (3.5 tonnes in NI) or the trailer weight exceeds the unladen weight of the tow vehicle then the driver will need to pass an additional test for category B+E. As a guide, the latest design of 30 ft twin axle boat trailer has a laden weight of 2500 kg; it appears likely that the unladen weight of the tow vehicle would be less than 2500 kg and this set-up would require a category B+E licence (Allowances vary in NI If you passed a category B+E test before 19 January 2013 (within the UK). Minibus-Passenger carrying vehicle with 9–16 passenger seats not operating for hire or reward: This vehicle would fall into sub category ‘D1’ and could tow a trailer of up to 750 kg. In order to drive this vehicle a category ‘B’ driver (basic car test) would need to a) meet higher medical standards and b) pass a further test for category ‘D1’. If a trailer in excess of 750 kg is to be towed then the maximum combination weight is 12 tonnes and the laden weight of the trailer must not exceed the unladen weight of the mini bus. To comply with this requirement the driver would then have to take another test for sub category ‘D1+E’. To get to this situation a category ‘B’ driver would have to pass two additional tests, first the ‘D1’ test followed by the ‘D1+E’ test. (Also applies in NI, but allowances vary and other categories exist. See:  what license for towing (NI).

Trailer Towing

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